publications
publications by categories in reversed chronological order.
2024
- Efficient multicarbon formation in acidic CO2 reduction via tandem electrocatalysisYuanjun Chen✝, Xiao-Yan Li✝, Zhu Chen✝, Adnan Ozden, Jianan Erick Huang, Pengfei Ou, Juncai Dong, Jinqiang Zhang, Cong Tian, Byoung-Hoon Lee, Xinyue Wang, Shijie Liu, Qingyu Qu, Sasa Wang, Yi Xu, Rui Kai Miao, Yong Zhao, Yanjiang Liu, Chenyue Qiu, Jehad Abed, Hengzhou Liu, Heejong Shin, Dingsheng Wang, Yadong Li, David Sinton, and Edward H. Sargent*Nature Nanotechnology, 2024
The electrochemical reduction of CO2 in acidic conditions enables high single-pass carbon efficiency. However, the competing hydrogen evolution reaction reduces selectivity in the electrochemical reduction of CO2, a reaction in which the formation of CO, and its ensuing coupling, are each essential to achieving multicarbon (C2+) product formation. These two reactions rely on distinct catalyst properties that are difficult to achieve in a single catalyst. Here we report decoupling the CO2-to-C2+ reaction into two steps, CO2-to-CO and CO-to-C2+, by deploying two distinct catalyst layers operating in tandem to achieve the desired transformation. The first catalyst, atomically dispersed cobalt phthalocyanine, reduces CO2 to CO with high selectivity. This process increases local CO availability to enhance the C–C coupling step implemented on the second catalyst layer, which is a Cu nanocatalyst with a Cu–ionomer interface. The optimized tandem electrodes achieve 61% C2H4 Faradaic efficiency and 82% C2+ Faradaic efficiency at 800 mA cm−2 at 25 °C. When optimized for single-pass utilization, the system reaches a single-pass carbon efficiency of 90 ± 3%, simultaneous with 55 ± 3% C2H4 Faradaic efficiency and a total C2+ Faradaic efficiency of 76 ± 2%, at 800 mA cm−2 with a CO2 flow rate of 2 ml min−1.
- Site-selective protonation enables efficient carbon monoxide electroreduction to acetateXinyue Wang✝, Yuanjun Chen✝, Feng Li✝, Rui Kai Miao✝, Jianan Erick Huang, Zilin Zhao, Xiao-Yan Li, Roham Dorakhan, Senlin Chu, Jinhong Wu, Sixing Zheng, Weiyan Ni, Dongha Kim, Sungjin Park, Yongxiang Liang, Adnan Ozden, Pengfei Ou, Yang Hou*, David Sinton*, and Edward H. Sargent*Nature Communications, 2024
Electrosynthesis of acetate from CO offers the prospect of a low-carbon-intensity route to this valuable chemical––but only once sufficient selectivity, reaction rate and stability are realized. It is a high priority to achieve the protonation of the relevant intermediates in a controlled fashion, and to achieve this while suppressing the competing hydrogen evolution reaction (HER) and while steering multicarbon (C2+) products to a single valuable product––an example of which is acetate. Here we report interface engineering to achieve solid/liquid/gas triple-phase interface regulation, and we find that it leads to site-selective protonation of intermediates and the preferential stabilization of the ketene intermediates: this, we find, leads to improved selectivity and energy efficiency toward acetate. Once we further tune the catalyst composition and also optimize for interfacial water management, we achieve a cadmium-copper catalyst that shows an acetate Faradaic efficiency (FE) of 75% with ultralow HER (<0.2% H2 FE) at 150 mA cm−2. We develop a high-pressure membrane electrode assembly system to increase CO coverage by controlling gas reactant distribution and achieve 86% acetate FE simultaneous with an acetate full-cell energy efficiency (EE) of 32%, the highest energy efficiency reported in direct acetate electrosynthesis.
- High-throughput screening of single-atom catalysts confined in monolayer black phosphorus for efficient nitrogen reduction reactionXiao-Yan Li✝, Manyi Duan✝, and Pengfei Ou*Nano Research, 2024
The discovery of metal-nitrogen centers as the active sites for electrolysis has aroused significant interest in utilizing single-atom catalysts for nitrogen reduction reaction (NRR). Properly designed nanostructured catalysts that strongly interact with nitrogen molecules (N2) can promote adsorption and activation, thereby resulting in efficient catalysts with high stability, activity, and selectivity. In this study, using density functional theory calculations, we selected monolayer black phosphorus (BP) as the substrate and screened a series of single-atom transition metals confined in tri-coordinated and tetra-coordinated active centers (without and with N dopants) to electro-catalyze NRR. As a result, we have identified two promising candidates (Hf1-N1P2-1 and Tc1-N4), which exhibit not only low overpotentials of 0.56 and 0.49 V but also high thermodynamic and electrochemical stability, as well as good selectivity towards NRR over the competing hydrogen evolution reaction. We also demonstrate the ability of Hf1-N1P2-1 and Tc1-N4 to activate and hydrogenate N2 by donating electrons and regulating charge transfer. This study not only predicts new BP-based promising catalysts but also provides guidance for the rational design of high-performance NRR electrocatalysts under ambient conditions.
- Unusual Sabatier principle on high entropy alloy catalysts for hydrogen evolution reactionsZhi Wen Chen✝, Jian Li✝, Pengfei Ou, Jianan Erick Huang, Zi Wen, LiXin Chen, Xue Yao, GuangMing Cai, Chun Cheng Yang*, Chandra Veer Singh*, and Qing Jiang*Nature Communications, 2024
The Sabatier principle is widely explored in heterogeneous catalysis, graphically depicted in volcano plots. The most desirable activity is located at the peak of the volcano, and further advances in activity past this optimum are possible by designing a catalyst that circumvents the limitation entailed by the Sabatier principle. Herein, by density functional theory calculations, we discovered an unusual Sabatier principle on high entropy alloy (HEA) surface, distinguishing the “just right” (ΔGH* = 0 eV) in the Sabatier principle of hydrogen evolution reaction (HER). A new descriptor was proposed to design HEA catalysts for HER. As a proof-of-concept, the synthesized PtFeCoNiCu HEA catalyst endows a high catalytic performance for HER with an overpotential of 10.8 mV at −10 mA cm−2 and 4.6 times higher intrinsic activity over the state-of-the-art Pt/C. Moreover, the unusual Sabatier principle on HEA catalysts can be extended to other catalytic reactions.
- Reduction of 5-Hydroxymethylfurfural to 2, 5-bis (hydroxymethyl) Furan at High Current Density Using a Ga-doped AgCu: Cationomer Hybrid ElectrocatalystCong Tian, Jiaqi Yu, Daojin Zhou, Huajie Ze, Hengzhou Liu, Yuanjun Chen, Rong Xia, Pengfei Ou, Weiyan Ni, Ke Xie*, and Edward H. Sargent*Advanced Materials, 2024
Hydrogenation of biomass-derived chemicals is of interest for the production of biofuels and valorized chemicals. Thermochemical processes for biomass reduction typically employ hydrogen as the reductant at elevated temperatures and pressures. Here, the authors investigate the direct electrified reduction of 5-hydroxymethylfurfural (HMF) to a precursor to bio-polymers, 2,5-bis(hydroxymethyl)furan (BHMF). Noting a limited current density in prior reports of this transformation, a hybrid catalyst consisting of ternary metal nanodendrites mixed with a cationic ionomer, the latter purposed to increase local pH and facilitate surface proton diffusion, is investigated. This approach, when implemented using Ga-doped Ag-Cu electrocatalysts designed for p–d orbital hybridization, steered selectivity to BHMF, achieving a faradaic efficiency (FE) of 58% at 100 mA cm−2 and a production rate of 1 mmol cm−2 h−1, the latter a doubling in rate compared to the best prior reports.
- Selective Electrified Propylene-to-Propylene Glycol Oxidation on Activated Rh-Doped PdJianan Erick Huang✝, Yiqing Chen✝, Pengfei Ou✝, Xueda Ding✝, Yu Yan, Roham Dorakhan, Yanwei Lum, Xiao-Yan Li, Yang Bai, Chengqian Wu, Mengyang Fan, Mi Gyoung Lee, Rui Kai Miao, Yanjiang Liu, Colin O’Brien, Jinqiang Zhang, Cong Tian, Yongxiang Liang, Yi Xu, Mingchuan Luo*, David Sinton, and Edward H. Sargent*Journal of the American Chemical Society, 2024
Renewable-energy-powered electrosynthesis has the potential to contribute to decarbonizing the production of propylene glycol, a chemical that is used currently in the manufacture of polyesters and antifreeze and has a high carbon intensity. Unfortunately, to date, the electrooxidation of propylene under ambient conditions has suffered from a wide product distribution, leading to a low faradic efficiency toward the desired propylene glycol. We undertook mechanistic investigations and found that the reconstruction of Pd to PdO occurs, followed by hydroxide formation under anodic bias. The formation of this metastable hydroxide layer arrests the progressive dissolution of Pd in a locally acidic environment, increases the activity, and steers the reaction pathway toward propylene glycol. Rh-doped Pd further improves propylene glycol selectivity. Density functional theory (DFT) suggests that the Rh dopant lowers the energy associated with the production of the final intermediate in propylene glycol formation and renders the desorption step spontaneous, a concept consistent with experimental studies. We report a 75% faradic efficiency toward propylene glycol maintained over 100 h of operation.
- Ligand-modified nanoparticle surfaces influence CO electroreduction selectivityErfan Shirzadi✝, Qiu Jin✝, Ali Shayesteh Zeraati, Roham Dorakhan, Tiago J Goncalves, Jehad Abed, Byoung-Hoon Lee, Armin Sedighian Rasouli, Joshua Wicks, Jinqiang Zhang, Pengfei Ou, Victor Boureau, Sungjin Park, Weiyan Ni, Geonhui Lee, Cong Tian, Debora Motta Meira, David Sinton, Samira Siahrostami*, and Edward H. Sargent*Nature Communications, 2024
Improving the kinetics and selectivity of CO2/CO electroreduction to valuable multi-carbon products is a challenge for science and is a requirement for practical relevance. Here we develop a thiol-modified surface ligand strategy that promotes electrochemical CO-to-acetate. We explore a picture wherein nucleophilic interaction between the lone pairs of sulfur and the empty orbitals of reaction intermediates contributes to making the acetate pathway more energetically accessible. Density functional theory calculations and Raman spectroscopy suggest a mechanism where the nucleophilic interaction increases the sp2 hybridization of CO(ad), facilitating the rate-determining step, CO* to (CHO)*. We find that the ligands stabilize the (HOOC–CH2)* intermediate, a key intermediate in the acetate pathway. In-situ Raman spectroscopy shows shifts in C–O, Cu–C, and C–S vibrational frequencies that agree with a picture of surface ligand-intermediate interactions. A Faradaic efficiency of 70% is obtained on optimized thiol-capped Cu catalysts, with onset potentials 100 mV lower than in the case of reference Cu catalysts.
- Adaptive Catalyst Discovery Using Multicriteria Bayesian Optimization with Representation LearningJie Chen, Pengfei Ou, Yuxin Chang, Hengrui Zhang, Xiao-Yan Li, Edward H Sargent, and Wei Chen*arXiv preprint arXiv:2404.12445, 2024
High-performance catalysts are crucial for sustainable energy conversion and human health. However, the discovery of catalysts faces challenges due to the absence of efficient approaches to navigating vast and high-dimensional structure and composition spaces. In this study, we propose a high-throughput computational catalyst screening approach integrating density functional theory (DFT) and Bayesian Optimization (BO). Within the BO framework, we propose an uncertainty-aware atomistic machine learning model, UPNet, which enables automated representation learning directly from high-dimensional catalyst structures and achieves principled uncertainty quantification. Utilizing a constrained expected improvement acquisition function, our BO framework simultaneously considers multiple evaluation criteria. Using the proposed methods, we explore catalyst discovery for the CO2 reduction reaction. The results demonstrate that our approach achieves high prediction accuracy, facilitates interpretable feature extraction, and enables multicriteria design optimization, leading to significant reduction of computing power and time (10x reduction of required DFT calculations) in high-performance catalyst discovery.
- Bimetallic Metal Sites in Metal–Organic Frameworks Facilitate the Production of 1-Butene from Electrosynthesized EthyleneMi Gyoung Lee✝, Sharath Kandambeth✝, Xiao-Yan Li✝, Osama Shekhah, Adnan Ozden, Joshua Wicks, Pengfei Ou, Sasa Wang, Roham Dorakhan, Sungjin Park, Prashant M. Bhatt, Vinayak S. Kale, David Sinton, Mohamed Eddaoudi*, and Edward H. Sargent*Journal of the American Chemical Society, 2024
Converting CO2 to synthetic hydrocarbon fuels is of increasing interest. In light of progress in electrified CO2 to ethylene, we explored routes to dimerize to 1-butene, an olefin that can serve as a building block to ethylene longer-chain alkanes. With goal of selective and active dimerization, we investigate a series of metal–organic frameworks having bimetallic catalytic sites. We find that the tunable pore structure enables optimization of selectivity and that periodic pore channels enhance activity. In a tandem system for the conversion of CO2 to 1-C4H8, wherein the outlet cathodic gas from a CO2-to-C2H4 electrolyzer is fed directly (via a dehumidification stage) into the C2H4 dimerizer, we study the highest-performing MOF found herein: M′ = Ru and M″ = Ni in the bimetallic two-dimensional M′2(OAc)4M″(CN)4 MOF. We report a 1-C4H8 production rate of 1.3 mol gcat–1 h–1 and a C2H4 conversion of 97%. From these experimental data, we project an estimated cradle-to-gate carbon intensity of −2.1 kg-CO2e/kg-1-C4H8 when CO2 is supplied from direct air capture and when the required energy is supplied by electricity having the carbon intensity of wind.
2023
- Energy-and carbon-efficient CO2/CO electrolysis to multicarbon products via asymmetric ion migration–adsorptionAdnan Ozden✝, Jun Li✝*, Sharath Kandambeth✝, Xiao-Yan Li✝, Shijie Liu, Osama Shekhah, Pengfei Ou, Y Zou Finfrock, Ya-Kun Wang, Tartela Alkayyali, F. Pelayo Arquer, Vinayak S. Kale, Prashant M. Bhatt, Alexander H. Ip, Mohamed Eddaoudi*, Edward H. Sargent*, and David Sinton*Nature Energy, 2023
Carbon dioxide/monoxide (CO2/CO) electrolysis provides a means to convert emissions into multicarbon products. However, impractical energy and carbon efficiencies limit current systems. Here we show that these inefficiencies originate from uncontrolled gas/ion distributions in the local reaction environment. Understanding of the flows of cations and anions motivated us to seek a route to block cation migration to the catalyst surface—a strategy we instantiate using a covalent organic framework (COF) in bulk heterojunction with a catalyst. The π-conjugated hydrophobic COFs constrain cation (potassium) diffusion via cation–π interactions, while promoting anion (hydroxide) and gaseous feedstock adsorption on the catalyst surface. As a result, a COF-mediated catalyst enables electrosynthesis of multicarbon products from CO for 200 h at a single-pass carbon efficiency of 95%, an energy efficiency of 40% and a current density of 240 mA cm−2.
- Pressure dependence in aqueous-based electrochemical CO2 reductionLiang Huang✝, Ge Gao✝, Chaobo Yang✝, Xiao-Yan Li✝, Rui Kai Miao, Yanrong Xue, Ke Xie, Pengfei Ou, Cafer T Yavuz, Yu Han, Gaetano Magnotti*, David Sinton*, Edward H. Sargent*, and Xu Lu*Nature Communications, 2023
https://www.nature.com/articles/s41467-023-38775-0
- Strong-proton-adsorption Co-based electrocatalysts achieve active and stable neutral seawater splittingNing Wang✝, Pengfei Ou✝, Sung-Fu Hung✝, Jianan Erick Huang, Adnan Ozden, Jehad Abed, Ivan Grigioni, Clark Chen, Rui Kai Miao, Yu Yan, Jinqiang Zhang, Ziyun Wang, Roham Dorakhan, Ahmed Badreldin, Ahmed Abdel-Wahab, David Sinton, Yongchang Liu, Hongyan Liang*, and Edward H. Sargent*Advanced Materials, 2023
Direct electrolysis of pH-neutral seawater to generate hydrogen is an attractive approach for storing renewable energy. However, due to the anodic competition between the chlorine evolution and the oxygen evolution reaction (OER), direct seawater splitting suffers from a low current density and limited operating stability. Exploration of catalysts enabling an OER overpotential below the hypochlorite formation overpotential (≈490 mV) is critical to suppress the chloride evolution and facilitate seawater splitting. Here, a proton-adsorption-promoting strategy to increase the OER rate is reported, resulting in a promoted and more stable neutral seawater splitting. The best catalysts herein are strong-proton-adsorption (SPA) materials such as palladium-doped cobalt oxide (Co3–xPdxO4) catalysts. These achieve an OER overpotential of 370 mV at 10 mA cm−2 in pH-neutral simulated seawater, outperforming Co3O4 by a margin of 70 mV. Co3–xPdxO4 catalysts provide stable catalytic performance for 450 h at 200 mA cm−2 and 20 h at 1 A cm−2 in neutral seawater. Experimental studies and theoretical calculations suggest that the incorporation of SPA cations accelerates the rate-determining water dissociation step in neutral OER pathway, and control studies rule out the provision of additional OER sites as a main factor herein.
- Conversion of CO2 to multicarbon products in strong acid by controlling the catalyst microenvironmentYong Zhao✝, Long Hao✝, Adnan Ozden✝, Shijie Liu✝, Rui Kai Miao, Pengfei Ou, Tartela Alkayyali, Shuzhen Zhang, Jing Ning, Yongxiang Liang, Yi Xu, Mengyang Fan, Yuanjun Chen, Jianan Erick Huang, Ke Xie, Jinqiang Zhang, Fengwang O’Brien, Edward H. Sargent, and David Sinton*Nature Synthesis, 2023
Electrosynthesis of multicarbon products from the reduction of CO2 in acidic electrolytes is a promising approach to overcoming CO2 reactant loss in alkaline and neutral electrolytes; however, the proton-rich environment near the catalyst surface favours the hydrogen evolution reaction, leading to low energy efficiency for multicarbon products. Here we report a heterogeneous catalyst adlayer—composed of covalent organic framework nanoparticles and cation-exchange ionomers—that suppresses hydrogen evolution and promotes CO2-to-multicarbon conversion in strong acid. The imine and carbonyl-functionalized covalent organic framework regulates the ionomer structure, creating evenly distributed cation-carrying and hydrophilic–hydrophobic nanochannels that control the catalyst microenvironment. The resulting high local alkalinity and cation-enriched environment enables C–C coupling between 100 and 400 mA cm−2. A multicarbon Faradaic efficiency of 75% is achieved at 200 mA cm−2. The system demonstrates a full-cell multicarbon energy efficiency of 25%, which is a twofold improvement over the literature benchmark acidic system for the reduction of CO2.
- An ultrasensitive FET biosensor based on vertically aligned MoS2 nanolayers with abundant surface active sitesPengfei Song, Pengfei Ou, Yongjie Wang, Hang Yuan, Sixuan Duan, Longyan Chen, Hao Fu, Jun Song, and Xinyu Liu*Analytica Chimica Acta, 2023
Molybdenum disulfide (MoS2) nanolayers are one of the most promising two-dimensional (2D) nanomaterials for constructing next-generation field-effect transistor (FET) biosensors. In this article, we report an ultrasensitive FET biosensor that integrates a novel format of 2D MoS2, vertically-aligned MoS2 nanolayers (VAMNs), as the channel material for label-free detection of the prostate-specific antigen (PSA). The developed VAMNs-based FET biosensor shows two distinctive advantages. First, the VAMNs can be facilely grown using the conventional chemical vapor deposition (CVD) method, permitting easy fabrication and potential mass device production. Second, the unique advantage of the VAMNs for biosensor development lies in its abundant surface-exposed active edge sites that possess a high binding affinity with thiol-based linkers, which overcomes the challenge of molecule functionalization on the conventional planar MoS2 nanolayers. The high binding affinity between 11-mercaptoundecanoic acid and the VAMNs was demonstrated through experimental surface characterization and theoretical calculations via density functional theory. The FET biosensor allows rapid (within 20 min) and ultrasensitive PSA detection in human serum with simple operations (limit of detection: 800 fg mL−1). This FET biosensor offers excellent features such as ultrahigh sensitivity, ease of fabrication, and short assay time, and thereby possesses significant potential for early-stage diagnosis of life-threatening diseases.
- Supramolecular tuning of supported metal phthalocyanine catalysts for hydrogen peroxide electrosynthesisByoung-Hoon Lee✝, Heejong Shin✝, Armin Sedighian Rasouli✝, Hitarth Choubisa✝, Pengfei Ou, Roham Dorakhan, Ivan Grigioni, Geonhui Lee, Erfan Shirzadi, Rui Kai Miao, Joshua Wicks, Sungjin Park, Hyeon Seok Lee, Jinqiang Zhang, Yuanjun Chen, Zhu Chen, David Sinton, Taeghwan Hyeon*, Yung-Eun Sung*, and Edward H. Sargent*Nature Catalysis, 2023
Two-electron oxygen reduction offers a route to H2O2 that is potentially cost-effective and less energy-intensive than the industrial anthraquinone process. However, the catalytic performance of the highest performing prior heterogeneous electrocatalysts to H2O2 has lain well below the >300 mA cm−2 needed for capital efficiency. Herein, guided by computation, we present a supramolecular approach that utilizes oxygen functional groups in a carbon nanotube substrate that—when coupled with a cobalt phthalocyanine catalyst—improve cobalt phthalocyanine adsorption, preventing agglomeration; and that further generate an electron-deficient Co centre whose interaction with the key H2O2 intermediate is tuned towards optimality. The catalysts exhibit an overpotential of 280 mV at 300 mA cm−2 with turnover frequencies over 50 s−1 in a neutral medium, an order of magnitude higher activity compared with the highest performing prior H2O2 electrocatalysts. This performance is sustained for over 100 h of operation.
- A silver–copper oxide catalyst for acetate electrosynthesis from carbon monoxideRoham Dorakhan✝, Ivan Grigioni✝, Byoung-Hoon Lee✝, Pengfei Ou, Jehad Abed, Colin O’Brien, Armin Sedighian Rasouli, Milivoj Plodinec, Rui Kai Miao, Erfan Shirzadi, Joshua Wicks, Sungjin Park, Geonhui Lee*, Jinqiang Zhang, David Sinton, and Edward H. Sargent*Nature Synthesis, 2023
Acetic acid is an important chemical feedstock. The electrocatalytic synthesis of acetic acid from CO2 offers a low-carbon alternative to traditional synthetic routes, but the direct reduction from CO2 comes with a CO2 crossover energy penalty. CO electroreduction bypasses this, which motivates the interest in a cascade synthesis approach of CO2 to CO followed by CO to acetic acid. Here we report a catalyst design strategy in which off-target intermediates (such as ethylene and ethanol) in the reduction of CO to acetate are destabilized. On the optimized Ag–CuO2 catalyst, this destabilization of off-target intermediates leads to an acetate Faradaic efficiency of 70% at 200 mA cm−2. We demonstrate 18 hours of stable operation in a membrane electrode assembly; the system produced 5 wt% acetate at 100 mA cm−2 and a full-cell energy efficiency of 25%, a twofold improvement on the highest energy-efficient electrosynthesis in prior reports.
- Selective synthesis of butane from carbon monoxide using cascade electrolysis and thermocatalysis at ambient conditionsMi Gyoung Lee✝, Xiao-Yan Li✝, Adnan Ozden✝, Joshua Wicks✝, Pengfei Ou, Yuhang Li, Roham Dorakhan, Jaekyoung Lee, Hoon Kee Park, Jin Wook Yang, Bin Chen, Jehad Abed, Roberto dos Reis, Geonhui Lee, Jianan Erick Huang, Tao Peng, Ya-Huei(Cathy) Chin, David Sinton, and Edward H. Sargent*Nature Catalysis, 2023
It is of interest to extend the reach of CO2 and CO electrochemistry to the synthesis of products with molecular weights higher than the C1 and C2 seen in most prior reports carried out near ambient conditions. Here we present a cascade C1–C2–C4 system that combines electrochemical and thermochemical reactors to produce C4H10 selectively at ambient conditions. In a C2H4 dimerization reactor, we directly upgrade the gas outlet stream of the CO2 or CO electrolyser without purification. We find that CO, which is present alongside C2H4, enhances C2H4 dimerization selectivity to give C4H10 to 95%, a much higher performance than when a CO2 electrolyser is used instead. We achieve an overall two-stage CO-to-C4H10 cascade selectivity of 43%. Mechanistic investigations, complemented by density functional theory calculations reveal that increased CO coverage favours C2H4 dimerization and hydrogenation of *CxHy adsorbates, as well as destabilizes the *C4H9 intermediate, and so promotes the selective production of the target alkane.
- Doping shortens the metal/metal distance and promotes OH coverage in non-noble acidic oxygen evolution reaction catalystsNing Wang✝, Pengfei Ou✝, Rui Kai Miao✝, Yuxin Chang✝, Ziyun Wang✝, Sung-Fu Hung, Jehad Abed, Adnan Ozden, Hsuan-Yu Chen, Heng-Liang Wu, Jianan Erick Huang, Daojin Zhou, Weiyan Ni, Lizhou Fan, Yu Yan, Tao Peng, David Sinton, Yongchang Liu, Hongyan Liang*, and Edward H. Sargent*Journal of the American Chemical Society, 2023
Acidic water electrolysis enables the production of hydrogen for use as a chemical and as a fuel. The acidic environment hinders water electrolysis on non-noble catalysts, a result of the sluggish kinetics associated with the adsorbate evolution mechanism, reliant as it is on four concerted proton-electron transfer steps. Enabling a faster mechanism with non-noble catalysts will help to further advance acidic water electrolysis. Here, we report evidence that doping Ba cations into a Co3O4 framework to form Co3–xBaxO4 promotes the oxide path mechanism and simultaneously improves activity in acidic electrolytes. Co3–xBaxO4 catalysts reported herein exhibit an overpotential of 278 mV at 10 mA/cm2 in 0.5 M H2SO4 electrolyte and are stable over 110 h of continuous water oxidation operation. We find that the incorporation of Ba cations shortens the Co–Co distance and promotes OH adsorption, findings we link to improved water oxidation in acidic electrolyte.
- Isolated Cu-Sn diatomic sites for enhanced electroreduction of CO2 to COWei Liu✝, Haoqiang Li✝, Pengfei Ou✝, Jing Mao, Lili Han*, Jun Song, Jun Luo, and Huolin L Xin*Nano Research, 2023
Electrochemical CO2 reduction reaction (CO2RR) to high-value product, CO, not only provides a key feedstock for the well-established Fischer—Tropsch process but also mitigates the greenhouse effect. However, it suffers from sluggish reaction kinetics, competitive hydrogen evolution reaction, and low selectivity. Herein, we report non-precious Cu-Sn diatomic sites anchored on nitrogen-doped porous carbon (CuSn/NPC) as an efficient catalyst for CO2RR to CO. The catalyst exhibits outstanding selectivity with CO Faradaic efficiency (FE) up to 99.1%, much higher than those of individual Cu (66.2%) and Sn (51.3%) single-atom catalysts. Moreover, high stability is confirmed by consecutive 24 h electrolysis with high selectivity from CO2 to CO. Theoretical calculations reveal an obvious activation of CO2 with weakened C—O bonds and distorted CO2 configuration upon chemisorption on the CuSn/NPC catalyst. It is also suggested CuSn/NPC is more selective for the CO2RR with dominant CO production during the electrolysis, rather than the competing hydrogen evolution reaction.
- Basal plane activation of two-dimensional transition metal dichalcogenides via alloying for the hydrogen evolution reaction: first-principles calculations and machine learning predictionYiqing Chen, Ying Zhao, Pengfei Ou*, and Jun Song*Journal of Materials Chemistry A, 2023
Two-dimensional transition metal dichalcogenides (2D TMDCs) show promise as potential inexpensive electrocatalysts for the hydrogen evolution reaction (HER). However, their performance is bottlenecked by the inertness of the basal plane. The present study demonstrates alloying as a viable route to address such limitations. A machine learning workflow based on density functional theory (DFT) calculations has been established to predict the HER activity and stability for a series of 2D cation-mixed TMDC alloys of various compositions. The results showed that alloying exhibits a substantial effect in reducing the Gibbs free energy of hydrogen adsorption (ΔGH) on the basal plane, able to render optimal ΔGH for the HER for certain TMDC alloys. The stability prediction of these TMDC alloys further showed their potential to be synthesized in experiments. The mechanism underlying this alloying induced basal plane activation originates from the electronic effect, in particular the p-band shifting, resulting from the chemical composition variation. The findings are expected to serve as guidance for the rational design and discovery of TMDC alloys for catalytic applications.
- Surface hydroxide promotes CO2 electrolysis to ethylene in acidic conditionsYufei Cao✝, Zhu Chen✝, Peihao Li, Adnan Ozden, Pengfei Ou, Weiyan Ni, Jehad Abed, Erfan Shirzadi, Jinqiang Zhang, David Sinton, Jun Ge*, and Edward H. Sargent*Nature Communications, 2023
Performing CO2 reduction in acidic conditions enables high single-pass CO2 conversion efficiency. However, a faster kinetics of the hydrogen evolution reaction compared to CO2 reduction limits the selectivity toward multicarbon products. Prior studies have shown that adsorbed hydroxide on the Cu surface promotes CO2 reduction in neutral and alkaline conditions. We posited that limited adsorbed hydroxide species in acidic CO2 reduction could contribute to a low selectivity to multicarbon products. Here we report an electrodeposited Cu catalyst that suppresses hydrogen formation and promotes selective CO2 reduction in acidic conditions. Using in situ time-resolved Raman spectroscopy, we show that a high concentration of CO and OH on the catalyst surface promotes C-C coupling, a finding that we correlate with evidence of increased CO residence time. The optimized electrodeposited Cu catalyst achieves a 60% faradaic efficiency for ethylene and 90% for multicarbon products. When deployed in a slim flow cell, the catalyst attains a 20% energy efficiency to ethylene, and 30% to multicarbon products.
- Constrained C2 adsorbate orientation enables CO-to-acetate electroreductionJian Jin✝, Joshua Wicks✝, Qiuhong Min✝, Jun Li✝, Yongfeng Hu, Jingyuan Ma, Yu Wang, Zheng Jiang, Yi Xu, Ruihu Lu, Gangzheng Si, Panagiotis Papangelakis, Mohsen Shakouri, Qunfeng Xiao, Pengfei Ou, Xue Wang, Zhu Chen, Wei Zhang, Kesong Yu, Jiayang Song, Xiaohang Jiang, Peng Qiu, Yuanhao Lou, Dan Wu, Yu Mao, Adnan Ozden, Chundong Wang, Bao Yu Xia, Xiaobing Hu, Vinayak P. Dravid, Yun-Mui Yiu, Tsun-Kong Sham, Ziyun Wang, David Sinton, Liqiang Mai*, Edward H. Sargent*, and Yuanjie Pang*Nature, 2023
The carbon dioxide and carbon monoxide electroreduction reactions, when powered using low-carbon electricity, offer pathways to the decarbonization of chemical manufacture1,2. Copper (Cu) is relied on today for carbon–carbon coupling, in which it produces mixtures of more than ten C2+ chemicals3,4,5,6: a long-standing challenge lies in achieving selectivity to a single principal C2+ product7,8,9. Acetate is one such C2 compound on the path to the large but fossil-derived acetic acid market. Here we pursued dispersing a low concentration of Cu atoms in a host metal to favour the stabilization of ketenes10—chemical intermediates that are bound in monodentate fashion to the electrocatalyst. We synthesize Cu-in-Ag dilute (about 1 atomic per cent of Cu) alloy materials that we find to be highly selective for acetate electrosynthesis from CO at high *CO coverage, implemented at 10 atm pressure. Operando X-ray absorption spectroscopy indicates in situ-generated Cu clusters consisting of <4 atoms as active sites. We report a 12:1 ratio, an order of magnitude increase compared to the best previous reports, in the selectivity for acetate relative to all other products observed from the carbon monoxide electroreduction reaction. Combining catalyst design and reactor engineering, we achieve a CO-to-acetate Faradaic efficiency of 91% and report a Faradaic efficiency of 85% with an 820-h operating time. High selectivity benefits energy efficiency and downstream separation across all carbon-based electrochemical transformations, highlighting the importance of maximizing the Faradaic efficiency towards a single C2+ product11.
- Single-site decorated copper enables energy-and carbon-efficient CO2 methanation in acidic conditionsMengyang Fan✝, Rui Kai Miao✝, Pengfei Ou✝, Yi Xu✝, Zih-Yi Lin, Tsung-Ju Lee, Sung-Fu Hung, Ke Xie, Jianan Erick Huang, Weiyan Ni, Jun Li, Yong Zhao, Adnan Ozden, Colin P. O’Brien, Yuanjun Chen, Yurou Celine Xiao, Shijie Liu, Joshua Wicks, Xue Wang, Jehad Abed, Erfan Shirzadi, Edward H. Sargent*, and David Sinton*Nature Communications, 2023
Renewable CH4 produced from electrocatalytic CO2 reduction is viewed as a sustainable and versatile energy carrier, compatible with existing infrastructure. However, conventional alkaline and neutral CO2-to-CH4 systems suffer CO2 loss to carbonates, and recovering the lost CO2 requires input energy exceeding the heating value of the produced CH4. Here we pursue CH4-selective electrocatalysis in acidic conditions via a coordination method, stabilizing free Cu ions by bonding Cu with multidentate donor sites. We find that hexadentate donor sites in ethylenediaminetetraacetic acid enable the chelation of Cu ions, regulating Cu cluster size and forming Cu-N/O single sites that achieve high CH4 selectivity in acidic conditions. We report a CH4 Faradaic efficiency of 71% (at 100 mA cm−2) with <3% loss in total input CO2 that results in an overall energy intensity (254 GJ/tonne CH4), half that of existing electroproduction routes.
- Cationic-group-functionalized electrocatalysts enable stable acidic CO2 electrolysisMengyang Fan✝, Jianan Erick Huang✝, Rui Kai Miao✝, Yu Mao✝, Pengfei Ou✝, Feng Li, Xiao-Yan Li, Yufei Cao, Zishuai Zhang, Jinqiang Zhang, Yu Yan, Adnan Ozden, Weiyan Ni, Ying Wang, Yong Zhao, Zhu Chen, Behrooz Khatir, Colin P. O’Brien, Yi Xu, Xiao Yurou Celine, Geoffrey I. N. Waterhouse, Kevin Golovin, Ziyun Wang*, Edward H. Sargent*, and David Sinton*Nature Catalysis, 2023
Acidic electrochemical CO2 reduction (CO2R) addresses CO2 loss and thus mitigates the energy penalties associated with CO2 recovery; however, acidic CO2R suffers low selectivity. One promising remedy—using a high concentration of alkali cations—steers CO2R towards multi-carbon (C2+) products, but these same alkali cations result in salt formation, limiting operating stability to <15 h. Here we present a copper catalyst functionalized with cationic groups (CG) that enables efficient CO2 activation in a stable manner. By replacing alkali cations with immobilized benzimidazolium CG within ionomer coatings, we achieve over 150 h of stable CO2R in acid. We find the water-management property of CG minimizes proton migration that enables operation at a modest voltage of 3.3 V with mildly alkaline local pH, leading to more energy-efficient CO2R with a C2+ Faradaic efficiency of 80 ± 3%. As a result, we report an energy efficiency of 28% for acidic CO2R towards C2+ products and a single-pass CO2 conversion efficiency exceeding 70%.
- Paired Electrosynthesis of H2 and acetic acid at A/cm2 current densitiesCong Tian✝, Xiao-Yan Li✝, Vivian E Nelson✝, Pengfei Ou, Daojin Zhou, Yuanjun Chen, Jinqiang Zhang, Jianan Erick Huang, Ning Wang, Jiaqi Yu, Hengzhou Liu, Cheng Liu, Yi Yang, Tao Peng, Yong Zhao, Byoung-Hoon Lee, Sasa Wang, Erfan Shirzadi, Zhu Chen, Rui Kai Miao, David Sinton*, and Edward H. Sargent*ACS Energy Letters, 2023
Industrial water splitting pairs cathodic hydrogen evolution with oxygen evolution at the anode, the latter generating low-value oxygen as the oxidative product. We reasoned that replacing the oxygen evolution reaction (OER) with anodic electrosynthesis of acetic acid from ethanol at industrial current densities could be a route to increase the economic efficiency of green hydrogen production. We partition the selective oxidation of ethanol to acetic acid into two mechanistically distinct transformations: first ethanol oxidation followed by the production of *OH. Density functional theory (DFT) studies show that the aldehyde-derived intermediate CH3CO* from ethanol oxidation and the *OH radical from water dissociation are both needed in the electroproduction of acetic acid. Operando Fourier transform infrared (FTIR) spectroscopy identifies the corresponding aldehyde intermediates on the anode surface. Based on these mechanistic findings, we develop a vacancy-rich IrRuOx catalyst and achieve selective electrotransformation of ethanol to acetic acid at a generation rate of 30 mmol/cm2/h and a partial current density of 3 A/cm2, fully 10× higher than in the previous highest-activity reports.
- Selective electrochemical synthesis of urea from nitrate and CO2 via relay catalysis on hybrid catalystsYuting Luo✝, Ke Xie✝, Pengfei Ou✝, Chayse Lavallais✝, Tao Peng, Zhu Chen, Zhiyuan Zhang, Ning Wang, Xiao-Yan Li, Ivan Grigioni, Bilu Liu, David Sinton, Jennifer B. Dunn*, and Edward H. Sargent*Nature Catalysis, 2023
The nitrogen cycle needed for scaled agriculture relies on energy- and carbon-intensive processes and generates nitrate-containing wastewater. Here we focus on an alternative approach—the electrified co-electrolysis of nitrate and CO2 to synthesize urea. When this is applied to industrial wastewater or agricultural runoff, the approach has the potential to enable low-carbon-intensity urea production while simultaneously providing wastewater denitrification. We report a strategy that increases selectivity to urea using a hybrid catalyst: two classes of site independently stabilize the key intermediates needed in urea formation, *CO2NO2 and *COOHNH2, via a relay catalysis mechanism. A Faradaic efficiency of 75% at wastewater-level nitrate concentrations (1,000 ppm NO3− [N]) is achieved on Zn/Cu catalysts. The resultant catalysts show a urea production rate of 16 µmol h−1 cm−2. Life-cycle assessment indicates greenhouse gas emissions of 0.28 kg CO2e per kg urea for the electrochemical route, compared to 1.8 kg CO2e kg−1 for the present-day route.
- Light-driven synthesis of C2H6 from CO2 and H2O on a bimetallic AuIr composite supported on InGaN nanowiresBaowen Zhou✝*, Yongjin Ma✝, Pengfei Ou✝, Zhengwei Ye✝, Xiao-Yan Li, Srinivas Vanka, Tao Ma, Haiding Sun, Ping Wang, Peng Zhou, Jason K. Cooper, Yixin Xiao, Ishtiaque Ahmed Navid, Jun Pan, Jun Song*, and Zetian Mi*Nature Catalysis, 2023
Generation of C2+ compounds from sunlight, carbon dioxide and water provides a promising path for carbon neutrality. Central to the construction of a rational artificial photosynthesis integrated device is the requirement for a catalyst to break the bottleneck of C–C coupling. Here, based on operando spectroscopy measurements, theoretical calculations and feedstock experiments, it is discovered that gold, in conjunction with iridium, can catalyse the reduction of CO2, achieving C–C coupling by insertion of CO2 into –CH3. Due to a combination of optoelectronic and catalytic properties, the assembly of AuIr with InGaN nanowires on silicon enables the achievement of a C2H6 activity of 58.8 mmol g−1 h−1 with a turnover number of 54,595 over 60 h. A light-to-fuel efficiency of 0.59% for solar fuel production from CO2 and H2O is achieved without any other energy inputs. This work provides a carbon-negative path for producing higher-order carbon compounds.
- Basal Plane Activation via Grain Boundaries in Monolayer MoS2 for Carbon Dioxide ReductionYing Zhao, Yiqing Chen, Pengfei Ou*, and Jun Song*ACS Catalysis, 2023
With the electrochemical carbon dioxide reduction reaction (CO2RR) being a promising method to reduce atmospheric carbon dioxide (CO2), transition metal dichalcogenides (TMDCs), such as molybdenum disulfide (MoS2), have recently risen as potential catalysts for CO2RR. However, pristine TMDCs are bottlenecked by the insufficiency of active sites in the basal plane. In this study, focusing on polycrystalline MoS2, we perform systematic density functional theory calculations to investigate the role of grain boundaries (GBs) on the catalytic performance of MoS2 for CO2RR. Our results show that most GBs contribute to lowering the reaction energy of the potential-limiting step in CO2RR. This effect can be further amplified with the introduction of S vacancies. In addition, the introduction of GBs with vacancies is shown to act as an effective method to break the scaling relations between reaction intermediates, which is crucial in improving catalytic efficiencies. Our findings demonstrate that defect engineering holds great potential to activate the basal plane of TMDCs for CO2RR, providing valuable insights into engineering TMDCs for high-performing CO2RR electrocatalysts.
- Epoxy-rich Fe Single Atom Sites Boost Oxygen Reduction ElectrocatalysisYufei Zhao✝, Ziyan Shen✝, Juanjuan Huo✝, Xianjun Cao, Pengfei Ou, Junpeng Qu, Xinming Nie*, Jinqiang Zhang*, Minghong Wu*, Guoxiu Wang, and Hao Liu*Angewandte Chemie International Edition, 2023
Electrocatalysts for highly efficient oxygen reduction reaction (ORR) are crucial for energy conversion and storage devices. Single-atom catalysts with maximized metal utilization and altered electronic structure are the most promising alternatives to replace current benchmark precious metals. However, the atomic level understanding of the functional role for each species at the anchoring sites is still unclear and poorly elucidated. Herein, we report Fe single atom catalysts with the sulfur and oxygen functional groups near the atomically dispersed metal centers (Fe1/NSOC) for highly efficient ORR. The Fe1/NSOC delivers a half-wave potential of 0.92 V vs. RHE, which is much better than those of commercial Pt/C (0.88 V), Fe single atoms on N-doped carbon (Fe1/NC, 0.89 V) and most reported nonprecious metal catalysts. The spectroscopic measurements reveal that the presence of sulfur group induces the formation of epoxy groups near the FeN4S2 centers, which not only modulate the electronic structure of Fe single atoms but also participate the catalytic process to improve the kinetics. The density functional theory calculations demonstrate the existence of sulfur and epoxy group engineer the charges of Fe reactive center and facilitate the reductive release of OH* (rate-limiting step), thus boosting the overall oxygen reduction efficiency.
- Electrified Cement Production via Anion-Mediated Electrochemical Calcium ExtractionRui Kai Miao✝, Ning Wang✝, Sung-Fu Hung, Wen-Yang Huang, Jinqiang Zhang, Yong Zhao, Pengfei Ou, Sasa Wang, Jonathan P Edwards, Cong Tian, Jingrui Han, Yi Xu, Mengyang Fan, Jianan Erick Huang, Yurou Celine Xiao, Alexander H. Ip, Yongxiang Liang, Edward H. Sargent*, and David Sinton*ACS Energy Letters, 2023
Cement production is a carbon-intensive industrial process, with the sector contributing ∼8% of global anthropogenic CO2 emissions. On average, producing each kilogram of cement leads to the emission of 1 kg of CO2─the combination of fuel combustion emissions and carbon released from the feedstock, limestone (CaCO3). Here we report electrochemical cement production based on anion-mediated electrochemical calcium extraction (ECE) that addresses both feedstock and energy emissions. The in situ-generated acidic electrolytes release the feedstock CO2 emissions at high purity, enabling direct carbon utilization or sequestration without costly capture and purification steps. Energy embodied within a separate H2 output stream is sufficient to sinter Ca(OH)2 to produce portland cement, thus removing the CO2 emissions associated with fuel combustion. We then replace CaCO3 with a carbon-free calcium feedstock, gypsum, thereby removing the CO2 emissions embodied in the feedstock. Technoeconomic analysis forecasts that this method could provide a viable, decarbonized cement alternative.
- Two-dimensional III-nitride alloys: electronic and chemical properties of monolayer Ga(1-x)AlxNYiqing Chen, Ying Zhao, Pengfei Ou*, and Jun Song*Physical Chemistry Chemical Physics, 2023
Potential applications of III-nitrides have led to their monolayer allotropes, i.e., two-dimensional (2D) III-nitrides, having attracted much attention. Recently, alloying has been demonstrated as an effective method to control the properties of 2D materials. In this study, the stability, and the electronic and chemical properties of monolayer Ga(1−x)AlxN alloys were investigated employing density functional theory (DFT) calculations and the cluster expansion (CE) method. The results show that 2D Ga(1−x)AlxN alloys are thermodynamically stable and complete miscibility in the alloys can be achieved at ambient temperature (>85 K). By analyzing CE results, the atomic arrangement of 2D Ga(1−x)AlxN was revealed, showing that Ga/Al atoms tend to mix with the Al/Ga atoms in their next nearest site. The band gaps of Ga(1−x)AlxN random alloys can be tuned by varying the chemical composition, and the corresponding bowing parameter was calculated as −0.17 eV. Biaxial tensile strain was also found to change the band gap values of Ga(1−x)AlxN random alloys ascribed to its modifications to the CBM positions. The chemical properties of Ga(1−x)AlxN can also be significantly altered by strain, making them good candidates as photocatalysts for water splitting. The present study can play a crucial role in designing and optimizing 2D III-nitrides for next-generation electronics and photocatalysis.
2022
- Efficient photoelectrochemical conversion of CO2 to syngas by photocathode engineeringSheng Chu✝*, Pengfei Ou✝, Roksana Tonny Rashid✝, Yuyang Pan, Daolun Liang, Huiyan Zhang, and Jun SongGreen Energy & Environment, 2022
The synthesis of renewable chemical fuels from CO2 and H2O via photoelectrochemical (PEC) route reprensents a promising room-temperature approach for transforming greenhouse gas into value-added chemicals (e.g., syngas), but to date it has been hampered by the lack of efficient photocathode for CO2 reduction. Herein, we report efficient PEC CO2 reduction into syngas by photocathode engineering. The photocathode is consisting of a planar p-n Si junction for strong light harvesting, GaN nanowires for efficient electron extraction and transfer, and Au/TiO2 for rapid electrocatalytic syngas production. The photocathode yields a record-high solar energy conversion efficiency of 2.3%. Furthermore, desirable syngas compositions with CO/H2 ratios such as 1:2 and 1:1 can be produced by simply varying the size of Au nanoparticle. Theoretical calculations reveal that the active sites for CO and H2 generation are the facet and undercoordinated sites of Au particles, respectively.
- Efficient electrosynthesis of n-propanol from carbon monoxide using a Ag–Ru–Cu catalystXue Wang✝, Pengfei Ou✝, Adnan Ozden, Sung-Fu Hung, Jason Tam, Christine M Gabardo, Jane Y Howe, Jared Sisler, Koen Bertens, F Pelayo Arquer, Rui Kai Miao, Colin P. O’Brien, Ziyun Wang, Jehad Armin Abed, Sedighian Rasouli, Mengjia Sun, Alexander H. Ip, David Sinton, and Edward H. Sargent*Nature Energy, 2022
The high-energy-density C3 fuel n-propanol is desired from CO2/CO electroreduction, as evidenced by propanol’s high market price per tonne (approximately US$ 1,400–1,600). However, CO electroreduction to n-propanol has shown low selectivity, limited production rates and poor stability. Here we report catalysts, identified using computational screening, that simultaneously facilitate multiple carbon–carbon coupling, stabilize C2 intermediates and promote CO adsorption, all leading to improved n-propanol electrosynthesis. Experimentally we construct the predicted optimal electrocatalyst based on silver–ruthenium co-doped copper. We achieve, at 300 mA cm−2, a high n-propanol Faradaic efficiency of 36% ± 3%, a C2+ Faradaic efficiency of 93% and single-pass CO conversion of 85%. The system exhibits 100 h stable n-propanol electrosynthesis. Technoeconomic analysis based on the performance of the pilot system projects profitability.
- Redox-mediated electrosynthesis of ethylene oxide from CO2 and waterYuhang Li✝, Adnan Ozden✝, Wan Ru Leow✝, Pengfei Ou✝, Jianan Erick Huang, Yuhang Wang, Koen Bertens, Yi Xu, Yuan Liu, Claudie Roy, Hao Jiang, David Sinton, Chunzhong Li*, and Edward H. Sargent*Nature Catalysis, 2022
The electrochemical production of ethylene oxide (EO) from CO2, water and renewable electricity could result in a net consumption of CO2. Unfortunately existing electrochemical CO2-to-EO conversions show impractical Faradaic efficiency (FE) and require a high energy input. Here we report a class of period-6-metal-oxide-modified iridium oxide catalysts that enable us to achieve improved CO2-to-EO conversion. Among barium, lanthanum, cerium and bismuth, we find that barium-oxide-loaded catalysts achieve an ethylene-to-EO FE of 90%. When we pair this with the oxygen reduction reaction at the cathode, we achieve an energy input of 5.3 MJ per kg of EO, comparable to that of existing (emissions-intensive) industrial processes. We have also devised a redox-mediated paired system that shows a 1.5-fold higher CO2-to-EO FE (35%) and uses a 1.2 V lower operating voltage than literature benchmark electrochemical systems.
- Single-walled black phosphorus nanotube as a NO2 gas sensorPengfei Ou*, Xiao Zhou, Xiao-Yan Li, Yiqing Chen, Cheng Chen, Fanchao Meng, and Jun Song*Materials Today Communications, 2022
An ab initio density functional theory study on the candidacy of single-walled black phosphorus nanotubes (BPNTs) towards sensing several common toxic gas molecules (NH3, CO, NO, NO2, and SO2) was conducted. Various adsorption characteristics, including the geometry, adsorption energy, charge transfer, band structure, and curvature effect were examined. Compared with MLBP, BPNTs are found to generally exhibit similar adsorption energy towards these molecules, whereas show selectively much stronger interaction with NO2. Analysis of charge density difference and band structure also indicates the electronic properties of BPNTs are significantly altered after the adsorption of NO2: transferring an indirect band gap of 0.3 eV for pristine (0, 9)BPNT to a metallic system. These facts collectively indicate the higher capability, sensitivity, and selectivity of BPNTs in the detection of NO2 compared to its planar counterpart. Moreover, the NO2 adsorption is found to be influenced by the curvature of BPNTs. Overall, findings from the present study indicate that BPNTs may serve as potential building blocks for high-performance gas sensors towards NO2 sensing.
- Accelerating CO2 Electroreduction to Multicarbon Products via Synergistic Electric–Thermal Field on Copper NanoneedlesBaopeng Yang✝, Kang Liu✝, HuangJingWei Li✝, Changxu Liu✝, Junwei Fu, Hongmei Li, Jianan Erick Huang, Pengfei Ou, Tartela Alkayyali, Chao Cai, Yuxia Duan, Hui Liu, Pengda An, Ning Zhang, Wenzhang Li, Xiaoqing Qiu, Chuankun Jia, Junhua Hu, Liyuan Chai, Zhang Lin, Yongli Gao, Masahiro Miyauchi, Emiliano Cortés, Stefan A. Maier*, and Min Liu*Journal of American Chemical Society, 2022
Electrochemical CO2 reduction is a promising way to mitigate CO2 emissions and close the anthropogenic carbon cycle. Among products from CO2RR, multicarbon chemicals, such as ethylene and ethanol with high energy density, are more valuable. However, the selectivity and reaction rate of C2 production are unsatisfactory due to the sluggish thermodynamics and kinetics of C–C coupling. The electric field and thermal field have been studied and utilized to promote catalytic reactions, as they can regulate the thermodynamic and kinetic barriers of reactions. Either raising the potential or heating the electrolyte can enhance C–C coupling, but these come at the cost of increasing side reactions, such as the hydrogen evolution reaction. Here, we present a generic strategy to enhance the local electric field and temperature simultaneously and dramatically improve the electric–thermal synergy desired in electrocatalysis. A conformal coating of ∼5 nm of polytetrafluoroethylene significantly improves the catalytic ability of copper nanoneedles (∼7-fold electric field and ∼40 K temperature enhancement at the tips compared with bare copper nanoneedles experimentally), resulting in an improved C2 Faradaic efficiency of over 86% at a partial current density of more than 250 mA cm–2 and a record-high C2 turnover frequency of 11.5 ± 0.3 s–1 Cu site–1. Combined with its low cost and scalability, the electric–thermal strategy for a state-of-the-art catalyst not only offers new insight into improving activity and selectivity of value-added C2 products as we demonstrated but also inspires advances in efficiency and/or selectivity of other valuable electro-/photocatalysis such as hydrogen evolution, nitrogen reduction, and hydrogen peroxide electrosynthesis.
- Electric metal contacts to monolayer blue phosphorus: electronic and chemical propertiesPengfei Ou*, Guoqiang Lan, Yiqing Chen, Xiao-Yan Li, Xiao Zhou, Cheng Chen, Fanchao Meng, and Jun Song*Applied Surface Science, 2022
The contact nature when monolayer blue phosphorus (blueP) interfaces with three transition metal electrodes (i.e., Pd, Ir, and Pt) was unraveled by the ab initio density functional theory calculations. Specifically, n-type Schottky contact is observed for Ir(1 1 1)-blueP, in contrast, p-type Schottky contacts are formed for Pd(1 1 1)- and Pt(1 1 1)-blueP. The Fermi level is pinned partially at metal-blueP interfaces due to two interfacial behaviors: one being the modification of metal work function caused by interface dipole formation ascribed to a redistribution of charges, and the other being the production of gap states that are dominated by P p-orbitals since the intralayer Psingle bondP bonds are weakened by the interfacial metal-P interactions. The incorporation of metal substrates would also significantly alter the chemical properties of the adsorbed monolayer blueP. The binding strength of hydrogen can be enhanced by as much as 0.9 eV, which resulted from two parts: one is the charge transfer from metal substrate to monolayer blueP rendering a stronger Hsingle bondP coupling; the other is a strong interfacial interaction after the hydrogen adsorption. The free energy change of H adsorption onto Ir(1 1 1)-blueP is as low as 0.16 eV which is comparable to the most efficient catalyst of Pt. These findings would provide theoretical guidance for the future design of electronic devices based on blueP and exploration of its potential in novel catalysts for hydrogen evolution reaction.
- A single-atom library for guided monometallic and concentration-complex multimetallic designsLili Han✝, Hao Cheng✝, Wei Liu✝, Haoqiang Li, Pengfei Ou, Ruoqian Lin, Hsiao-Tsu Wang, Chih-Wen Pao, Ashley R Head, Chia-Hsin Wang, Xiao Tong, Cheng-Jun Sun, Way-Faung Pong, Jun Luo*, Jin-Cheng Zheng*, and Huolin L. Xin*Nature Materials, 2022
Atomically dispersed single-atom catalysts have the potential to bridge heterogeneous and homogeneous catalysis. Dozens of single-atom catalysts have been developed, and they exhibit notable catalytic activity and selectivity that are not achievable on metal surfaces. Although promising, there is limited knowledge about the boundaries for the monometallic single-atom phase space, not to mention multimetallic phase spaces. Here, single-atom catalysts based on 37 monometallic elements are synthesized using a dissolution-and-carbonization method, characterized and analysed to build the largest reported library of single-atom catalysts. In conjunction with in situ studies, we uncover unified principles on the oxidation state, coordination number, bond length, coordination element and metal loading of single atoms to guide the design of single-atom catalysts with atomically dispersed atoms anchored on N-doped carbon. We utilize the library to open up complex multimetallic phase spaces for single-atom catalysts and demonstrate that there is no fundamental limit on using single-atom anchor sites as structural units to assemble concentration-complex single-atom catalyst materials with up to 12 different elements. Our work offers a single-atom library spanning from monometallic to concentration-complex multimetallic materials for the rational design of single-atom catalysts.
- Design of Ru-Ni diatomic sites for efficient alkaline hydrogen oxidationLili Han✝, Pengfei Ou✝, Wei Liu, Xiang Wang, Hsiao-Tsu Wang, Rui Zhang, Chih-Wen Pao, Xijun Liu*, Way-Faung Pong, Jun Song, Zhongbin Zhuang, Michael V. Mirkin, Jun Luo, and Huolin L. Xin*Science Advances, 2022
Anion exchange membrane fuel cells are limited by the slow kinetics of alkaline hydrogen oxidation reaction (HOR). Here, we establish HOR catalytic activities of single-atom and diatomic sites as a function of *H and *OH binding energies to screen the optimal active sites for the HOR. As a result, the Ru-Ni diatomic one is identified as the best active center. Guided by the theoretical finding, we subsequently synthesize a catalyst with Ru-Ni diatomic sites supported on N-doped porous carbon, which exhibits excellent catalytic activity, CO tolerance, and stability for alkaline HOR and is also superior to single-site counterparts. In situ scanning electrochemical microscopy study validates the HOR activity resulting from the Ru-Ni diatomic sites. Furthermore, in situ x-ray absorption spectroscopy and computational studies unveil a synergistic interaction between Ru and Ni to promote the molecular H2 dissociation and strengthen OH adsorption at the diatomic sites, and thus enhance the kinetics of HOR.
- High carbon utilization in CO2 reduction to multi-carbon products in acidic mediaYi Xie✝, Pengfei Ou✝, Xue Wang✝, Zhanyou Xu, Yuguang C Li, Ziyun Wang, Jianan Erick Huang, Joshua Wicks, Christopher McCallum, Ning Wang, Yuhang Wang, Tianxiang Chen, Benedict T. W. Lo, David Sinton, Jimmy C. Yu, Ying Wang*, and Edward H. Sargent*Nature Catalysis, 2022
Renewable electricity-powered CO2 reduction to multi-carbon (C2+) products offers a promising route to realization of low-carbon-footprint fuels and chemicals. However, a major fraction of input CO2 (>85%) is consumed by the electrolyte through reactions with hydroxide to form carbonate/bicarbonate in both alkaline and neutral reactors. Acidic conditions offer a solution to overcoming this limitation, but also promote the hydrogen evolution reaction. Here we report a design strategy that suppresses hydrogen evolution reaction activity by maximizing the co-adsorption of CO and CO2 on Cu-based catalysts to weaken H* binding. Using density functional theory studies, we found Pd–Cu promising for selective C2+ production over C1, with the lowest ∆GOCCOH* and ∆GOCCOH* - ∆GCHO*. We synthesized Pd–Cu catalysts and report a crossover-free system (liquid product crossover <0.05%) with a Faradaic efficiency of 89 ± 4% for CO2 to C2+ at 500 mA cm−2, simultaneous with single-pass CO2 utilization of 60 ± 2% to C2+.
- Abundant (110) Facets on PdCu₃ Alloy Promote Electrochemical Conversion of CO₂ to COJianwu Dong✝, Ying Cheng✝, Ying Li✝, Xianyun Peng, Rui Zhang, Hsiao-Tsu Wang, Chunyang Wang, Xiaoyan Li, Pengfei Ou, Chih-Wen Pao, Lili Han*, Way-Faung Pong, Zhang Lin, Jun Luo, and Huolin L. Xin*ACS Applied Materials & Interfaces, 2022
Electrochemical conversion of CO2 to high-value chemical fuels offers a promising strategy for managing the global carbon balance but faces huge challenges due to the lack of effective electrocatalysts. Here, we reported PdCu3 alloy nanoparticles with abundant exposed (110) facets supported on N-doped three-dimensional interconnected carbon frameworks (PdCu3/NC) as an efficient and durable electrocatalyst for electrochemical CO2 reduction to CO. The catalyst exhibits extremely high intrinsic CO2 reduction selectivity for CO production with a Faraday efficiency of nearly 100% at a mild potential of −0.5 V. Moreover, a rechargeable high-performance Zn–CO2 battery with PdCu3/NC as a cathode is developed to deliver a record-high energy efficiency of 99.2% at 0.5 mA cm–2 and rechargeable stability of up to 133 h. Theoretical calculations elucidate that the exposed (110) facet over PdCu3/NC is the active center for CO2 activation and rapid formation of the key *COOH intermediate.
- Chemically coupling SnO2 quantum dots and MXene for efficient CO2 electroreduction to formate and Zn–CO2 batteryLili Han✝*, Xianyun Peng✝, Hsiao-Tsu Wang✝, Pengfei Ou✝, Yuying Mi, Chih-Wen Pao, Jigang Zhou, Jian Wang, Xijun Liu, Way-Faung Pong, Jun Song, Zhang Lin, Jun Luo, and Huolin L. Xin*Proceedings of the National Academy of Sciences, 2022
Electrochemical conversion of CO2 into formate is a promising strategy for mitigating the energy and environmental crisis, but simultaneously achieving high selectivity and activity of electrocatalysts remains challenging. Here, we report low-dimensional SnO2 quantum dots chemically coupled with ultrathin Ti3C2Tx MXene nanosheets (SnO2/MXene) that boost the CO2 conversion. The coupling structure is well visualized and verified by high-resolution electron tomography together with nanoscale scanning transmission X-ray microscopy and ptychography imaging. The catalyst achieves a large partial current density of −57.8 mA cm−2 and high Faradaic efficiency of 94% for formate formation. Additionally, the SnO2/MXene cathode shows excellent Zn–CO2 battery performance, with a maximum power density of 4.28 mW cm−2, an open-circuit voltage of 0.83 V, and superior rechargeability of 60 h. In situ X-ray absorption spectroscopy analysis and first-principles calculations reveal that this remarkable performance is attributed to the unique and stable structure of the SnO2/MXene, which can significantly reduce the reaction energy of CO2 hydrogenation to formate by increasing the surface coverage of adsorbed hydrogen
- Abundant (110) facets on PdCu3 alloy promote electrochemical conversion of CO2 to COJianwu Dong✝, Ying Cheng✝, Ying Li✝, Xianyun Peng, Rui Zhang, Hsiao-Tsu Wang, Chunyang Wang, Xiaoyan Li, Pengfei Ou, Chih-Wen Pao, Lili Han*, Way-Faung Pong, Zhang Lin, Jun Luo, and Huolin L. Xin*ACS Applied Materials & Interfaces, 2022
Electrochemical conversion of CO2 to high-value chemical fuels offers a promising strategy for managing the global carbon balance but faces huge challenges due to the lack of effective electrocatalysts. Here, we reported PdCu3 alloy nanoparticles with abundant exposed (110) facets supported on N-doped three-dimensional interconnected carbon frameworks (PdCu3/NC) as an efficient and durable electrocatalyst for electrochemical CO2 reduction to CO. The catalyst exhibits extremely high intrinsic CO2 reduction selectivity for CO production with a Faraday efficiency of nearly 100% at a mild potential of −0.5 V. Moreover, a rechargeable high-performance Zn–CO2 battery with PdCu3/NC as a cathode is developed to deliver a record-high energy efficiency of 99.2% at 0.5 mA cm–2 and rechargeable stability of up to 133 h. Theoretical calculations elucidate that the exposed (110) facet over PdCu3/NC is the active center for CO2 activation and rapid formation of the key *COOH intermediate.
2021
- Modulating single-atom palladium sites with copper for enhanced ambient ammonia electrosynthesisLili Han✝, Zhouhong Ren✝, Pengfei Ou✝, Hao Cheng, Ning Rui, Lili Lin, Xijun Liu*, Longchao Zhuo, Jun Song*, Jiaqiang Sun, Jun Luo, and Huolin L. Xin*Angewandte Chemie, 2021
The electrochemical reduction of N2 to NH3 is emerging as a promising alternative for sustainable and distributed production of NH3. However, the development has been impeded by difficulties in N2 adsorption, protonation of *NN, and inhibition of competing hydrogen evolution. To address the issues, we design a catalyst with diatomic Pd-Cu sites on N-doped carbon by modulation of single-atom Pd sites with Cu. The introduction of Cu not only shifts the partial density of states of Pd toward the Fermi level but also promotes the d-2π* coupling between Pd and adsorbed N2, leading to enhanced chemisorption and activated protonation of N2, and suppressed hydrogen evolution. As a result, the catalyst achieves a high Faradaic efficiency of 24.8±0.8 % and a desirable NH3 yield rate of 69.2±2.5 μg h−1 mgcat.−1, far outperforming the individual single-atom Pd catalyst. This work paves a pathway of engineering single-atom-based electrocatalysts for enhanced ammonia electrosynthesis.
- Negative Poisson’s ratio in graphene Miura origamiFanchao Meng, Shuying Chen, Wenyan Zhang, Pengfei Ou, Jing Zhang, Cheng Chen*, and Jun Song*Mechanics of Materials, 2021
Hydrogenation is a viable approach in transforming two-dimensional (2D) nanosheets into three-dimensional (3D) nanoarchitectures. The present work reported self-folding of 2D graphene into 3D graphene Miura origami assisted by hydrogenation, and studied its Poisson’s ratio under external strain using molecular dynamics simulation and continuum modeling. It was found that the graphene Miura origami possesses negative Poisson’s ratio, being largely insensitive to the chirality of the folding creases and side lengths of the constituting parallelograms. We further demonstrated the good agreement of Poisson’s ratio between the continuum prediction and MD simulation, and identified the origin of their deviation as localized stress concentration at the quad-junction of the graphene Miura origami. The present study provides insights into designing novel 3D nanoarchitectures of programmable functionalities from 2D nanomaterials.
- A microfluidic field-effect transistor biosensor with rolled-up indium nitride microtubesPengfei Song, Hao Fu, Yongjie Wang, Cheng Chen, Pengfei Ou, Roksana Tonny Rashid, Sixuan Duan, Jun Song, Zetian Mi, and Xinyu Liu*Biosensors and Bioelectronics, 2021
Field-effect-transistor (FET) biosensors capable of rapidly detecting disease-relevant biomarkers have long been considered as a promising tool for point-of-care (POC) diagnosis. Rolled-up nanotechnology, as a batch fabrication strategy for generating three-dimensional (3D) microtubes, has been demonstrated to possess unique advantages for constructing FET biosensors. In this paper, we report a new approach combining the two fascinating technologies, the FET biosensor and the rolled-up microtube, to develop a microfluidic diagnostic biosensor. We integrated an excellent biosensing III-nitride material—indium nitride (InN)—into a rolled-up microtube and used it as the FET channel. The InN possesses strong, intrinsic, and stable electron accumulation ( 1013 cm−2) on its surface, thereby providing a high device sensitivity. Multiple rolled-up InN microtube FET biosensors fabricated on the same substrate were integrated with a microfluidic channel for convenient fluids handling, and shared the same external electrode (inserted into the microchannel outlet) for gating voltage modulation. Using human immunodeficiency virus (HIV) antibody as a model disease marker, we characterized the analytical performance of the developed biosensor and achieved a limit of detection (LOD) of 2.5 pM for serum samples spiked with HIV gp41 antibodies. The rolled-up InN microtube FET biosensor represents a new type of III-nitride-based FET biosensor and holds significant potential for practical POC diagnosis.
- Gold-in-copper at low *CO coverage enables efficient electromethanation of CO2Xue Wang✝, Pengfei Ou✝, Joshua Wicks✝, Yi Xie✝, Ying Wang✝, Jun Li, Jason Tam, Dan Ren, Jane Y Howe, Ziyun Wang, Adnan Ozden, Y. Zou Finfrock, Yi Xu, Yuhang Li, Armin Sedighian Rasouli, Koen Bertens, Alexander H. Ip, Michael Graetzel, David Sinton, and Edward H. Sargent*Nature Communications, 2021
The renewable-electricity-powered CO2 electroreduction reaction provides a promising means to store intermittent renewable energy in the form of valuable chemicals and dispatchable fuels. Renewable methane produced using CO2 electroreduction attracts interest due to the established global distribution network; however, present-day efficiencies and activities remain below those required for practical application. Here we exploit the fact that the suppression of *CO dimerization and hydrogen evolution promotes methane selectivity: we reason that the introduction of Au in Cu favors *CO protonation vs. C−C coupling under low *CO coverage and weakens the *H adsorption energy of the surface, leading to a reduction in hydrogen evolution. We construct experimentally a suite of Au-Cu catalysts and control *CO availability by regulating CO2 concentration and reaction rate. This strategy leads to a 1.6× improvement in the methane:H2 selectivity ratio compared to the best prior reports operating above 100 mA cm−2. We as a result achieve a CO2-to-methane Faradaic efficiency (FE) of (56 ± 2)% at a production rate of (112 ± 4) mA cm−2.
- Atomistic and continuum modeling of 3D graphene honeycombs under uniaxial in-plane compressionYiqing Chen, Fanchao Meng*, Xiaohan Bie, Pengfei Ou, and Jun Song*Computational Materials Science, 2021
Using large-scale molecular dynamics (MD) simulations in conjunction with continuum modeling, the deformation behaviors of three-dimensional (3D) graphene honeycomb structures under uniaxial in-plane compression have been systematically investigated. The stress-strain responses of graphene honeycombs were found to be dependent on the loading direction, prism size and lattice orientation, but little affected by the junction type. Two critical deformation events, i.e., elastic buckling and structural collapse, were identified, with the associated local and global structural changes associated at these critical events clarified. Continuum models accounting for the effect of lattice orientation and size-dependent yielding have been developed to quantitatively predict the threshold stresses for those critical deformation events. In addition, it has been demonstrated that the overall stress-strain curve of graphene honeycomb can also be reasonably well predicted via continuum modeling, albeit deviation at large strains due to effect of junction on cell wall bending. The present study provides critical mechanistic understanding and predictive tools for optimizing and designing 3D graphene honeycombs in small-scale applications.
- Gold adparticles on silver combine low overpotential and high selectivity in electrochemical CO2 conversionAdnan Ozden✝, Yanjiang Liu✝, Cao-Thang Dinh✝, Jun Li, Pengfei Ou, F Pelayo Arquer, Edward H Sargent*, and David Sinton*ACS Applied Energy Materials, 2021
Silver (Ag) catalysts enable high selectivity (>90%) in CO2-to-CO conversion at >100 mA cm–2; gold (Au) catalysts are active at lower overpotential, but with lower selectivity (<80%). Here we present an adparticle-functionalized catalyst that combines the benefits of each by uniting Au adparticles on the AgAu interface. Au adparticles modify the lattice and electronic structure of Ag and lower the free energy change required to form *COOH. We demonstrate selective and low-overpotential CO2-to-CO conversion at >490 mA cm–2 in a flow cell. In a membrane electrode assembly, the catalyst achieves 90% CO selectivity and 33% CO energy efficiency over 60 h.
- Boride-derived oxygen-evolution catalystsNing Wang✝, Aoni Xu✝, Pengfei Ou✝, Sung-Fu Hung✝, Adnan Ozden, Ying-Rui Lu, Jehad Abed, Ziyun Wang, Yu Yan, Meng-Jia Sun, Yujian Xia, Mei Han, Jingrui Han, Kaili Yao, Feng-Yi Wu, Pei-Hsuan Chen, Alberto Vomiero, Xuhui Seifitokaldani, Yongchang David Sinton, Edward H. Sargent*, and Hongyan Liang*Nature Communications, 2021
Metal borides/borates have been considered promising as oxygen evolution reaction catalysts; however, to date, there is a dearth of evidence of long-term stability at practical current densities. Here we report a phase composition modulation approach to fabricate effective borides/borates-based catalysts. We find that metal borides in-situ formed metal borates are responsible for their high activity. This knowledge prompts us to synthesize NiFe-Boride, and to use it as a templating precursor to form an active NiFe-Borate catalyst. This boride-derived oxide catalyzes oxygen evolution with an overpotential of 167 mV at 10 mA/cm2 in 1 M KOH electrolyte and requires a record-low overpotential of 460 mV to maintain water splitting performance for over 400 h at current density of 1 A/cm2. We couple the catalyst with CO reduction in an alkaline membrane electrode assembly electrolyser, reporting stable C2H4 electrosynthesis at current density 200 mA/cm2 for over 80 h.
2020
- Highly efficient binary copper-iron catalyst for photoelectrochemical carbon dioxide reduction toward methaneBaowen Zhou✝, Pengfei Ou✝, Nick Pant, Shaobo Cheng, Srinivas Vanka, Sheng Chu, Roksana Tonny Rashid, Gianluigi Botton, Jun Song*, and Zetian Mi*Proceedings of the National Academy of Sciences, 2020
A rational design of an electrocatalyst presents a promising avenue for solar fuels synthesis from carbon dioxide (CO2) fixation but is extremely challenging. Herein, we use density functional theory calculations to study an inexpensive binary copper−iron catalyst for photoelectrochemical CO2 reduction toward methane. The calculations of reaction energetics suggest that Cu and Fe in the binary system can work in synergy to significantly deform the linear configuration of CO2 and reduce the high energy barrier by stabilizing the reaction intermediates, thus spontaneously favoring CO2 activation and conversion for methane synthesis. Experimentally, the designed CuFe catalyst exhibits a high current density of −38.3 mA⋅cm−2 using industry-ready silicon photoelectrodes with an impressive methane Faradaic efficiency of up to 51%, leading to a distinct turnover frequency of 2,176 h−1 under air mass 1.5 global (AM 1.5G) one-sun illumination.
- Atomistic simulations of vibration and damping in three-dimensional graphene honeycomb nanomechanical resonatorsBing Li, Yulan Wei, Fanchao Meng, Pengfei Ou, Yuying Chen, Lei Che, Cheng Chen*, and Jun SongSuperlattices and Microstructures, 2020
The vibration characteristics and damping of three-dimensional graphene honeycombs (3DGHs) were studied using molecular dynamics simulations and continuum modeling. Both zigzag and armchair 3DGHs were considered. Longitudinal harmonic excitation was applied on the free end of the cantilever honeycomb along the axial direction. Based on the curves of the vibration responses and the amplitude-frequency characteristic of the 3DGH, it was revealed that the amplitude of vibration response and the resonant frequencies of the 3DGHs were influenced by both the excitation frequency and the amplitude of the excitation force. Moreover, the vibration characteristics of the 3DGHs exhibit spring softening nonlinearity, with greater nonlinearity observed as the exciting force increases. The linear and nonlinear damping of the 3DGHs were further evaluated using the loss factor in the sub-resonant regime under various excitation forces, showing that the 3DGH as a resonator can be excited at higher frequencies of GHz with a small loss factor than graphene and CNT. This study demonstrates the relationships of resonant frequencies and damping with the frequency and amplitude of the excitation force in 3DGHs, providing theoretical foundation for designing 3DGH nanomechanical resonators.
- A complete computational route to predict reduction of thermal conductivities of complex oxide ceramics by doping: A case study of La2Zr2O7Guoqiang Lan, Pengfei Ou, Cheng Chen, and Jun Song*Journal of Alloys and Compounds, 2020
Rare-earth (RE) zirconate pyrochlores, of low thermal conductivity and high temperature stability, are widely considered as a candidate material group for thermal barrier coatings (TBCs). Doping of a RE zirconate pyrochlore has been shown to be one possible method towards additional reduction in the thermal conductivity. Focusing on lanthanum zirconate (La2Zr2O7) as a representative RE zirconate pyrochlore, we systematically investigated the effect of various doping elements, Gd, Y, Yb, In, Sc, Ce and Hf, on the thermal conductivity. A complete computational route, based on first-principles calculations, to predict the reduction of thermal conductivity by doping, has been developed. Employing first-principles calculations combined with thermodynamic modeling, the defects resulted from doping are explicitly clarified, with their concentrations determined considering the chemical environment. The phonon-defect scattering is then evaluated and the resultant reduction of thermal conductivity is determined from single-mode relaxation-time approximation. Good agreement has been achieved between our model predictions and available experimental data. The present study established a complete computational route, based on first-principles calculations, to predict the reduction of thermal conductivity by doping, not only for RE zirconate pyrochlores, but also for other complex oxide ceramics.
- Controlling the null photonic gap and zero refractive index in photonic superlattices with temperature-controllable-refractive-index materialsYe Wu, Pengfei Ou, Ling Zhang*, Yingcheng Lin, and Jiquan YangJOSA B, 2020
Temperature-adjustable optical properties of two types of one-dimensional photonic superlattices made from lithium niobate or liquid crystal are theoretically investigated. The control of band structures and density of states is achieved through the temperature with various values of refractive index, layer width, and propagation wavelength. It is presented that a null photonic gap appears at certain temperature points, which are decided by the ratio of layer width and the refractive index. It is shown that the spatial average of the wave vector ⟨k⟩ vanishes at a specific temperature as functions of the layer thickness and refractive index. The values of the temperature corresponding to zero-refractive-index (zero-⟨n⟩) are demonstrated to be suppressed when the refractive index or the ratio of the layer width is enhanced. Null photonic gap and zero-⟨n⟩ can appear simultaneously at certain wavelengths in the range of visible light, which can be modulated by the temperature. This implies the importance of one-dimensional photonic superlattices made from temperature-controllable-refractive-index materials for many important practical applications.
- Synthesis of praseodymium-and molybdenum-sulfide nanoparticles for dye-photodegradation and near-infrared deep-tissue imagingYe Wu, Pengfei Ou, Jun Song, Ling Zhang, Yingcheng Lin*, Pengfei Song*, and Jian Xu*Materials Research Express, 2020
Development of nanoparticles with multi-functionalities is of great importance. In this study, praseodymium sulfide (Pr2S3) and molybdenum sulfide (MoS2) nanoparticles were synthesized. The structural, morphological and optical properties of the as-obtained products were investigated by XRD, XPS, TEM, UV–vis-NIR spectroscopy, and photoluminescence spectroscopy. Pr2S3 is found to be used in selective photodegradation of fluorescein sodium salt. MoS2 can be utilized for selective photodegradation of rhodamine B. In the mixture of rhodamine B, fluorescein sodium salt and rhodamine 6 G, most of rhodamine B and part of fluorescein sodium salt are optically degraded by Pr2S3. In the mixture of rhodamine B, fluorescein sodium salt and rhodamine 6 G, part of fluorescein sodium salt and most of rhodamine B is degraded by MoS2. Moreover, they emit near-infrared fluorescence (800–1100 nm) when excited by the 785 nm light. Deep tissues imaging with high-contrast is shown, utilizing a nanoparticle-filled centrifuge tube covered with animal tissues (pig Bacon meat). Maximum imaging depth below the tissue surface of 1 cm is achieved. Our work provides a rapid yet efficient procedure to make nanoparticles for dual-application-potential in dye-photodegradation and near-infrared deep tissue imaging.
- Interface engineering in CeO2 (1 1 1) facets decorated with CdSe quantum dots for photocatalytic hydrogen evolutionYongjin Ma✝, Pengfei Ou✝, Ziyu Wang*, Anquan Zhu, Lili Lu, Yuhui Zhang, Weixuan Zeng, Jun Song*, and Jun Pan*Journal of Colloid and Interface Science, 2020
The interfaces of heterostructures have been widely studied in the field of photocatalytic H2 evolution reaction (HER). In the present study, the CdSe QDs/CeO2(1 1 1) heterostructures were synthesized by wet chemistry method. The CdSe QDs/CeO2(1 1 1)-0.075 showed higher photocatalytic H2 evolution with 283.32 µmol g-1h−1, because of the enhanced light absorbance intensity and edge, lower recombination, higher separation and transfer, as well as longer lifetime of the photogenerated carrier. Density functional theory (DFT) calculations further confirmed that the enhanced HER activity of CdSe QDs/CeO2(1 1 1) heterostructures is resulted from a stronger water adsorption, a lower energy barrier of water dissociation and a more optimal free energy of hydrogen adsorption than CdSe and CeO2. The strategy of construction heterostructures provides a promising pathway for enhancing the performance of photocatalytic H2 evolution as well as other catalytic reactions.
- Decoupling Strategy for Enhanced Syngas Generation from Photoelectrochemical CO2 ReductionSheng Chu✝, Pengfei Ou✝, Roksana Tonny Rashid✝, Pegah Ghamari✝, Renjie Wang, Hong Nhung Tran, Songrui Zhao, Huiyan Zhang, Jun Song*, and Zetian Mi*iScience, 2020
Photoelectrochemical CO2 reduction into syngas (a mixture of CO and H2) provides a promising route to mitigate greenhouse gas emissions and store intermittent solar energy into value-added chemicals. Design of photoelectrode with high energy conversion efficiency and controllable syngas composition is of central importance but remains challenging. Herein, we report a decoupling strategy using dual cocatalysts to tackle the challenge based on joint computational and experimental investigations. Density functional theory calculations indicate the optimization of syngas generation using a combination of fundamentally distinctive catalytic sites. Experimentally, by integrating spatially separated dual cocatalysts of a CO-generating catalyst and a H2-generating catalyst with GaN nanowires on planar Si photocathode, we report a record high applied bias photon-to-current efficiency of 1.88% and controllable syngas products with tunable CO/H2 ratios (0–10) under one-sun illumination. Moreover, unassisted solar CO2 reduction with a solar-to-syngas efficiency of 0.63% is demonstrated in a tandem photoelectrochemical cell.
- Electrosynthesis of ammonia using porous bimetallic Pd–Ag nanocatalysts in liquid-and gas-phase systemsMohammadreza Nazemi, Pengfei Ou, Abdulaziz Alabbady, Luke Soule, Alan Liu, Jun Song, Todd A Sulchek, Meilin Liu, and Mostafa A El-Sayed*ACS Catalysis, 2020
Cost-effective production of ammonia via electrochemical nitrogen reduction reaction (NRR) hinges on N2 electrolysis at high current densities with suitable selectivity and activity. Here, we report our findings in electrochemical NRR for ammonia synthesis using porous bimetallic Pd–Ag nanocatalysts in both gas-phase and liquid-phase electrochemical cells at current densities above 1 mA cm–2 under ambient conditions. While the gas-phase cell has lower Ohmic losses and higher energy efficiency, the liquid-phase cell achieved higher selectivity and Faradaic efficiency, attributed to the presence of concentrated N2 molecules dissolved in an aqueous electrolyte and the hydration effects. The liquid cell demonstrated notable performance for electrocatalytic NRR, achieving an NH3 production rate of 45.6 ± 3.7 μg cm–2 h–1 at a cell voltage of −0.6 V (vs RHE) and current density of 1.1 mA cm–2, corresponding to a Faradaic efficiency of ∼19.6% and an energy efficiency of ∼9.9%. Similarly, the gas-phase cell achieved a NH3 yield rate of 19.4 ± 2.1 μg cm–2 h–1 at −0.07 V (vs RHE) and 1.15 mA cm–2 with a Faradaic efficiency of 7.9% and an energy efficiency of 27.1%. Further, operando surface-enhanced Raman spectroscopy and density functional theory (DFT) are used to identify intermediate species relevant to the NRR at the electrode–electrolyte interfaces to provide insights into the NRR mechanism on Pd–Ag nanoparticles. This work highlights the importance of design and optimization of cell configuration in addition to the modification of the catalyst to achieve high-performance N2 electrolysis for ammonia synthesis.
- Mineralogical phase transformation of Fe containing sphalerite at acidic environments in the presence of Cu2+Yisheng Zhang, Hongbo Zhao*, Xiaoyu Meng, Pengfei Ou, Xin Lv, Luyuan Zhang, Lixin Liu, Fashang Chen, and Guanzhou QiuJournal of Hazardous Materials, 2020
Dissolution of the exposed sphalerite (marmatite) in abandoned mining sites and tailings may exacerbate acid and metalliferous drainage (AMD) hazards. Cupric ions are inevitable ions in AMD systems but its action mechanism on the dissolution of sphalerite is still unclear. In this work, the possible phase transition from sphalerite to chalcopyrite is firstly discovered in acidic cupric ions solution according to the results of Raman and (synchrotron radiation-based) X-ray (micro-) diffractometer spectra, which should be an important reason that mediates the dissolution of sphalerite. Results of DFT calculations reveal the underlying mechanism that Cu2+ can selectively replace zinc in marmatite lattices and further diffuse into the matrix. Additionally, a strong correlation between the cupric ion consumption with the pH value variation is discussed and the effects of the formed new phase on the dissolution kinetics of marmatite were researched. According to this work, the action mechanism of cupric ions on sphalerite dissolution in acidic environments is furtherly clarified.
- Basal Plane Activation in Monolayer MoTe2 for Hydrogen Evolution Reaction via Phase BoundariesYiqing Chen, Pengfei Ou, Xiaohan Bie, and Jun Song*Journal of Materials Chemistry A, 2020
Two-dimensional transition metal dichalcogenides (2D TMDCs) have attracted tremendous interest as a prominent material group providing inexpensive electrocatalysts for the hydrogen evolution reaction (HER). In the present study, using monolayer MoTe2 as a representative, we demonstrated that phase boundaries can provide a viable pathway to activate the basal plane of 2D TMDCs for enhanced HER performance. Comprehensive first-principles calculations have been performed to examine the energetics and structural stabilities of possible 2H/1T′ phase boundary configurations. Three categories of sites, Te, Mo and hollow sites, have been identified at energetically stable phase boundaries, as potential catalytic centers for the HER, all indicating enhanced HER activity compared to that of the pristine basal lattice. In particular, the hollow sites, a new group of sites induced by phase boundaries, show great promise by exhibiting a Gibbs free energy (ΔGH) near the thermoneutral value for hydrogen adsorption, comparable to that of Pt. The mechanisms underlying hydrogen adsorption at phase boundaries were then revealed, shown to be attributed to the unique local hydrogen adsorption geometries and electronic structures at phase boundaries. Our study clarifies the important mechanistic aspects underlying hydrogen activation at phase boundaries, providing valuable theoretical insights into designing a new class of high-performance HER electrocatalysts based on 2D TMDCs.
- Few-atomic-layers iron for hydrogen evolution from water by photoelectrocatalysisBaowen Zhou✝, Pengfei Ou✝, Roksana Tonny Rashid✝, Srinivas Vanka, Kai Sun, Lin Yao, Haiding Sun, Jun Song*, and Zetian Mi*iScience, 2020
The carbon-free production of hydrogen from water splitting holds grand promise for the critical energy and environmental challenges. Herein, few-atomic-layers iron (FeFAL) anchored on GaN nanowire arrays (NWs) is demonstrated as a highly active hydrogen evolution reaction catalyst, attributing to the spatial confinement and the nitrogen-terminated surface of GaN NWs. Based on density functional theory calculations, the hydrogen adsorption on FeFAL:GaN NWs is found to exhibit a significantly low free energy of −0.13 eV, indicative of high activity. Meanwhile, its outstanding optoelectronic properties are realized by the strong electronic coupling between atomic iron layers and GaN(10ī0) together with the nearly defect-free GaN NWs. As a result, FeFAL:GaN NWs/n+-p Si exhibits a prominent current density of ∼ −30 mA cm−2 at an overpotential of ∼0.2 V versus reversible hydrogen electrode with a decent onset potential of +0.35 V and 98% Faradaic efficiency in 0.5 mol/L KHCO3 aqueous solution under standard one-sun illumination.
- Local modulation of single-atomic Mn sites for enhanced ambient ammonia electrosynthesisLili Han✝, Machuan Hou✝, Pengfei Ou✝, Hao Cheng, Zhouhong Ren, Zhixiu Liang, J Anibal Boscoboinik, Adrian Hunt, Iradwikanari Waluyo, Shusheng Zhang, Longchao Zhuo, Jun Song, Xijun Liu*, Jun Luo, and Huolin L. Xin*ACS Catalysis, 2020
Rationally tuning the local structures of single-atomic active sites for the electrocatalytic N2 reduction reaction (NRR) remains an urgent but worthwhile research topic. Herein, we accomplish the local modulation of single-atomic Mn sites and construct single Mn–O3N1 sites anchored on porous carbon (Mn–O3N1/PC) by delicately controlling the Mn–O bonding conditions. The constructed structures are confirmed via the combination of atomic-scale imaging, Raman spectroscopy, synchrotron radiation-based soft and hard X-ray absorption spectroscopies, and X-ray photoelectron spectroscopy. The Mn–O3N1/PC catalyst yields an NH3 yield rate of 66.41 μg h–1 mgcat.–1 (corresponding to 1.56 mg h–1 mgMn–1) at −0.35 V versus reversible hydrogen electrode, which is about four times that on the control Mn–N4/PC catalyst. The enhanced NRR performance is ascribed to its unique geometry and electronic structures, which not only facilitate the adsorption and activation of the N2 molecule but also lower the free energy change of the potential-determining step.
2019
- Superior sensing properties of black phosphorus as gas sensors: a case study on the volatile organic compoundsPengfei Ou, Pengfei Song, Xinyu Liu, and Jun Song*Advanced Theory and Simulations, 2019
The unique structure and prominent properties of black phosphorus (BP) and its monolayer and multilayers in device applications have attracted significant attention to this elemental 2D material. In this study, a comprehensive evaluation of the candidacy of monolayer BP as a channel material for high-performance volatile organic compound (VOC) sensors is conducted combining first-principles density functional theory calculations and non-equilibrium Green’s function formalism. The adsorption configurations and energetics of several typical VOCs (ethanol, propionaldehyde, acetone, toluene, and hexane) on monolayer BP are examined and it is demonstrated that VOCs generally exhibit stronger interaction with monolayer BP than with the widely studied monolayer MoS2, indicative of monolayer BP potentially being a more sensitive VOC sensor. Monolayer BP is shown to exhibit highly anisotropic transport behaviors, whereas the absolute modification of current–voltage responses due to VOCs is found to show a trend that is direction independent. Moreover, the adsorption of VOCs on monolayer BP is strong enough to resist thermal disturbance, yet allows fast recovery time. The results suggest that BP is a compelling and feasible candidate for sensing applications of VOCs.
- Structural evolution of oxygen on the surface of TiAlN: Ab initio molecular dynamics simulationsFangyu Guo, Jianchuan Wang*, Yong Du, David Holec, Pengfei Ou, Hao Zhou, Li Chen, and Yi KongApplied Surface Science, 2019
We have employed ab initio molecular dynamics simulations to study the oxidation behavior of TiAlN hard coatings as a function of Al content and temperature. Results show that for TiAlN with a low Al content (Ti0.75Al0.25N), Ti atoms can always bond with O atoms, while Al atoms bond with O only at a higher temperature. For Ti0.5Al0.5N, both Al and Ti can bond with O atoms, irrespective of temperature. Through analyzing the displacement height of O-bonded metal atoms, we suggest that titanium oxide nucleates at the outermost layer of Ti0.75Al0.25N while the outermost layer after Ti0.5Al0.5N is exposed to oxygen is aluminum oxide. Our simulation results predict, in agreement with experiment, that Ti0.5Al0.5N has superior oxidation resistance in comparison with Ti0.75Al0.25N. This study provides an atomistic insight to the initial stage of the oxidation process, which is else difficult to observe experimentally.
- Effects of material heterogeneity on self-rolling of strained membranesCheng Chen, Pengfei Song, Fanchao Meng, Pengfei Ou, Guoqiang Lan, Xinyu Liu, and Jun Song*Extreme Mechanics Letters, 2019
The present work studies the effects of strained membranes. An analytical framework has been established to predict self-rolling curvatures of strained bilayer membranes containing heterogeneous material elements. The accuracy of the framework is validated through molecular dynamics (MD) simulations on the heterogeneous CdTexS1-x/CdTe bilayer system. Moreover, numerical simulations using finite-element modeling (FEM) have been performed to examine the role of heterogeneous elements in the complex helical rolling. It has been demonstrated that both the rolling direction and rollup curvature can be predictively controlled by modulating the material heterogeneity and layer thickness. The present study points to a new pathway towards predictive design and tuning of complex 3D structures based on strained membranes through incorporation of heterogeneous elements.