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    Chinese Journal of Catalysis
    2022, Vol. 43, No. 11
    Online: 18 November 2022

    Cover: The study of the hydrogen evolution reaction on iron modified Pt(111) single crystal surfaces provides new clues to the understanding of the parameters that govern the rate of this reaction. Information from measurements using the laser induced temperature jump experiments allows to establish relationships between the interfacial electric field, the polarization of interfacial water molecules and the rate of H2 production. Read more about the article behind the cover on page 2826–2836.
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    Editorial
    Celebrate the polysemy of fundamental in electrocatalysis
    Shengli Chen, Jun Huang
    2022, 43 (11):  2743-2745.  DOI: 10.1016/S1872-2067(22)64171-8
    Abstract ( 71 )   HTML ( 24 )   PDF (737KB) ( 72 )  
    Perspective
    Theoretical understanding of electrocatalysis beyond thermodynamic analysis
    Huan Li, Chenxi Guo, Jun Long, Xiaoyan Fu, Jianping Xiao
    2022, 43 (11):  2746-2756.  DOI: 10.1016/S1872-2067(22)64090-7
    Abstract ( 193 )   HTML ( 32 )   PDF (7187KB) ( 275 )  

    As the green and sustainable development of human society highly relies on renewable energy, it has been recognized that electrocatalysis is a key technology to this end. High efficient ways of carbon-neutralization (eCO2RR), reverse artificial nitrogen cycle (RANC), and oxygen chemistry (OER and ORR) all can be driven by electrocatalysis. Advanced theoretical study is an important means to fundamentally understanding electrocatalytic reactions. Herein, we review a few significant issues in theoretical electrocatalysis. First, electrochemical barriers and potential effects are essential for a more accurate description of reaction mechanism and activity. Meanwhile, consideration of competitive reaction path is also one of the important aspects, as novel insights and anomalous volcano trend can be obtained. Finally, a microenvironment exerted by confined space can tune the capacitance of electrochemical interface and (electro)chemical potential of proton, resulting in a possibility to improve reaction activity, which opens a new avenue for design of catalyst.

    Reviews
    Surface-enhanced vibrational spectroscopies in electrocatalysis: Fundamentals, challenges, and perspectives
    Hai-Sheng Su, Xiaoxia Chang, Bingjun Xu
    2022, 43 (11):  2757-2771.  DOI: 10.1016/S1872-2067(22)64157-3
    Abstract ( 177 )   HTML ( 18 )   PDF (2624KB) ( 136 )  

    Electrocatalysis offers a promising approach towards chemical synthesis driven by renewable energy. Molecular level understanding of the electrochemical interface remains challenging due to its compositional and structural complexity. In situ interfacial specific characterization techniques could help uncover structure-function relationships and reaction mechanism. To this end, electrochemical surface-enhanced Raman spectroscopy (SERS) and surface-enhanced infrared absorption spectroscopy (SEIRAS) thrive as powerful techniques to provide fingerprint information of interfacial species at reaction conditions. In this review, we first introduce the fundamentals of SERS and SEIRAS, followed by discussion regarding the technical challenges and potential solutions. Finally, we highlight future directions for further development of surface-enhanced spectroscopic techniques for electrocatalytic studies.

    Fundamental aspects in CO2 electroreduction reaction and solutions from in situ vibrational spectroscopies
    Hong Li, Kun Jiang, Shou-Zhong Zou, Wen-Bin Cai
    2022, 43 (11):  2772-2791.  DOI: 10.1016/S1872-2067(22)64095-6
    Abstract ( 625 )   HTML ( 14 )   PDF (5862KB) ( 310 )  

    Using renewable energy to drive carbon dioxide reduction reaction (CO2RR) electrochemically into chemicals with high energy density is an efficient way to achieve carbon neutrality, where the effective utilization of CO2 and the storage of renewable energy are realized. The reactivity and selectivity of CO2RR depend on the structure and composition of the catalyst, applied potential, electrolyte, and pH of the solution. Besides, multiple electron and proton transfer steps are involved in CO2RR, making the reaction pathways even more complicated. In pursuit of molecular-level insights into the CO2RR processes, in situ vibrational methods including infrared, Raman and sum frequency generation spectroscopies have been deployed to monitor the dynamic evolution of catalyst structure, to identify reactive intermediates as well as to investigate the effect of local reaction environment on CO2RR performance. This review summarizes key findings from recent electrochemical vibrational spectrosopic studies of CO2RR in addressing the following issues: the CO2RR mechanisms of different pathways, the role of surface-bound CO species, the compositional and structural effects of catalysts and electrolytes on CO2RR activity and selectivity. Our perspectives on developing high sensitivity wide-frequency infrared spectroscopy, coupling different spectroelectrochemical methods and implementing operando vibrational spectroscopies to tackle the CO2RR process in pilot reactors are offered at the end.

    Restructuring of well-defined Pt-based electrode surfaces under mild electrochemical conditions
    Jie Wei, Wei Chen, Da Zhou, Jun Cai, Yan-Xia Chen
    2022, 43 (11):  2792-2801.  DOI: 10.1016/S1872-2067(22)64100-7
    Abstract ( 139 )   HTML ( 6 )   PDF (5942KB) ( 139 )  

    Since the 1980s, single-crystal Pt electrodes with well-defined surface structures have been deemed stable under mild electrochemical conditions (e.g., in the potential region of electric double layers, underpotential deposition of hydrogen, or mild hydrogen evolution/OH adsorption) and have served as model electrodes for unraveling the structure-performance relation in electrocatalysis. With the advancement of in situ electrochemical microscopy/spectroscopy techniques, subtle surface restructuring under mild electrochemical conditions has been achieved in the last decade. Surface restructuring can considerably modify electrocatalytic properties by generating/destroying highly active sites, thereby interfering with the deduction of the structure-performance relation. In this review, we summarize recent progress in the restructuring of well-defined Pt(-based) electrode surfaces under mild electrochemical conditions. The importance of the meticulous structural characterization of Pt electrodes before, during, and after electrochemical measurements is demonstrated using CO adsorption/oxidation, hydrogen adsorption/evolution, and oxygen reduction as examples. The implications of present findings for correctly identifying the reaction mechanisms and kinetics of other electrocatalytic systems are also briefly discussed.

    Emerging two-dimensional metallenes: Recent advances in structural regulations and electrocatalytic applications
    Jiandong Wu, Xiao Zhao, Xiaoqiang Cui, Weitao Zheng
    2022, 43 (11):  2802-2814.  DOI: 10.1016/S1872-2067(21)64022-6
    Abstract ( 342 )   HTML ( 28 )   PDF (12714KB) ( 346 )  

    Benefiting from the ultrahigh specific surface areas, highly accessible surface atoms, and highly tunable microscopic structures, the two-dimensional metallenes as nanocatalysts have displayed promising performance for various electrocatalytic reactions. Herein, we reviewed recent advances on metallenes in structural regulations including defect, phase, strain, interface, doping, and alloying engineering strategies and their applications in energy electrocatalytic reactions involving oxygen reduction reaction, carbon dioxide reduction reaction, hydrogen evolution reaction, and small molecules oxidation reaction. Finally, we proposed the future challenges and directions in this emerging area.

    Communications
    Enhanced single-nanoparticle collisions for the hydrogen evolution reaction in a confined microchannel
    Si-Min Lu, Mengjie Chen, Huilin Wen, Hao-Wei Wang, Ziyi Yu, Yi-Tao Long
    2022, 43 (11):  2815-2819.  DOI: 10.1016/S1872-2067(21)64034-2
    Abstract ( 111 )   HTML ( 10 )   PDF (2499KB) ( 164 )  
    Supporting Information

    Single nanoparticle (NP) collisions technique has been widely employed in electrocatalysis. However, the short collision duration of single NPs hinders the further improvement in their electrocatalytic performance. Here, to increase the dynamic collision duration of single NPs in the electron tunneling region, enhanced near-wall hindered diffusion is introduced in the stochastic collision process by coupling a Au ultramicroelectrode (UME) with a confined microchannel. In the case of single palladium nanoparticle (Pd NP) collisions for the hydrogen evolution reaction (HER), the hydrodynamic trapping confined in the microchannel effectively permits the activation of the HER on the single Pd NPs. The microchannel-based Au UME is promising in the application of single-NP collisions to energy conversion.

    In-situ electrochemical surface-enhanced Raman spectroscopy in metal/polyelectrolyte interfaces
    Li-Wen Wu, Mo-Li Huang, Yun-Xiao Yang, Yi-Fan Huang
    2022, 43 (11):  2820-2825.  DOI: 10.1016/S1872-2067(21)64041-X
    Abstract ( 81 )   HTML ( 8 )   PDF (1302KB) ( 74 )  
    Supporting Information

    Polyelectrolyte becomes more and more popular in electrocatalysis. The understanding of electrode/polyelectrolyte interfaces at the molecular level is important for guiding further the polyelectrolyte-based electrocatalysis. Herein, we demonstrate an in-situ surface-enhanced Raman spectroscopic method by using a three-electrode spectroelectrochemical cell towards characterizing the electrode/polyelectrolyte interfaces. The Ag/AgCl and Ag/Ag2O electrodes are used as the reference electrode in the acidic and the alkaline systems, respectively. The working electrode is made of a transparent carbon thin film which loads the electrocatalysts. The applications of this method are demonstrated through the in-situ characterizations of the p-methylthiophenol adsorbed on the Au and Pt and the electrochemical oxidation of Au on polyelectrolyte membranes. The potential-dependent spectral features of these two systems show that this method is a powerful tool for investigating the electrode/polyelectrolyte interfaces in electrocatalysis.

    Articles
    Effect of the interfacial electric field on the HER on Pt(111) modified with iron adatoms in alkaline media
    Francisco J. Sarabia, Víctor Climent, Juan M. Feliu
    2022, 43 (11):  2826-2836.  DOI: 10.1016/S1872-2067(22)64141-X
    Abstract ( 110 )   HTML ( 7 )   PDF (2881KB) ( 68 )  

    The study of the hydrogen evolution reaction (HER) aimed to reach a deeper understanding of the parameters that control the rate of this reaction is of great importance given the technical relevance of hydrogen production as an energy vector in the so-called hydrogen economy. In previous works, laser-induced temperature jump (LITJ) experiments on Pt(111) modified with Ni(OH)2 in alkaline media have revealed the importance of the interfacial electric field in the rate of the HER. It was hypothesised that small amounts of Ni(OH)2 cause a decrease of the electric field because of a negative shift of the pzfc toward the onset of the hydrogen evolution. In this work, to test the validity of this hypothesis, the study has been extended to Pt(111) surfaces modified with Fe(OH)2. The modified surfaces have been studied voltammetrically, and the voltammetric charges have been analysed. The voltammograms show a peak in the hydrogen evolution region that suggest the transformation in the adlayer from Fe(II) to Fe(0). In agreement with the coulometric analysis, the voltammetric features in the OH adsorption region would be related with the oxidation to the +3 valence state. The results obtained with LITJ method reflect the existence of a strong interaction of the Fe oxophilic species with the water molecules, shifting the potential of maximum entropy away from the onset of the HER. Hence, the most catalytic surface is the one with the lowest Fe coverage.

    Understanding surface charge effects in electrocatalysis. Part 2: Hydrogen peroxide reactions at platinum
    Jun Huang, Victor Climent, Axel Groß, Juan M. Feliu
    2022, 43 (11):  2837-2849.  DOI: 10.1016/S1872-2067(22)64138-X
    Abstract ( 258 )   HTML ( 10 )   PDF (2517KB) ( 177 )  
    Supporting Information

    Electrocatalytic activity is influenced by the surface charge on the solid catalyst. Conventionally, our attention has been focused on how the surface charge shapes the electric potential and concentration of ionic reactant(s) in the local reaction zone. Taking H2O2 redox reactions at Pt(111) as a model system, we reveal a peculiar surface charge effect using ab initio molecular dynamics simulations of electrified Pt(111)-water interfaces. In this scenario, the negative surface charge on Pt(111) repels the O-O bond of the reactant (H2O2) farther away from the electrode surface. This leads to a higher activation barrier for breaking the O-O bond. Incorporating this microscopic mechanism into a microkinetic-double-layer model, we are able to semi-quantitatively interpret the pH-dependent activity of H2O2 redox reactions at Pt(111), especially the anomalously suppressed activity of H2O2 reduction with decreasing electrode potential. The relevance of the present surface charge effect is also examined in wider scenarios with different electrolyte cations, solution pHs, crystal facets of the catalyst, and model parameters. In contrast with previous mechanisms focusing on how surface charge influences the local reaction condition at a fixed reaction plane, the present work gives an example in which the location of the reaction plane is adjusted by the surface charge.

    Solvation structure and dynamics of Li and LiO2 and their transformation in non-aqueous organic electrolyte solvents from first-principles simulations
    Behnaz Rahmani Didar, Axel Groß
    2022, 43 (11):  2850-2857.  DOI: 10.1016/S1872-2067(22)64098-1
    Abstract ( 161 )   HTML ( 6 )   PDF (3748KB) ( 101 )  

    Density functional theory calculations together with ab initio molecular dynamics (AIMD) simulations have been used to study the solvation, diffusion and transformation of Li+ and LiO2 upon O2 reduction in three organic electrolytes. These processes are critical for the performance of Li-air batteries. Apart from studying the structure of the solvation shells in detail, AIMD simulations have been used to derive the diffusivity and together with the Blue Moon ensemble approach to explore LiO2 formation from Li+ and O2- and the subsequent disproportionation of 2LiO2 into Li2O2 + O2. By comparing the results of the simulations to gas phase calculations, the impact of electrolytes on these reactions is assessed which turns out to be more pronounced for the ionic species involved in these reactions.

    Understanding fundamentals of electrochemical reactions with tender X-rays: A new lab-based operando X-ray photoelectron spectroscopy method for probing liquid/solid and gas/solid interfaces across a variety of electrochemical systems
    Chiyan Liu, Qiao Dong, Yong Han, Yijing Zang, Hui Zhang, Xiaoming Xie, Yi Yu, Zhi Liu
    2022, 43 (11):  2858-2870.  DOI: 10.1016/S1872-2067(22)64092-0
    Abstract ( 86 )   HTML ( 7 )   PDF (2567KB) ( 80 )  
    Supporting Information

    Electrocatalysis is key to improving energy efficiency, reducing carbon emissions, and providing a sustainable way of meeting global energy needs. Therefore, elucidating electrochemical reaction mechanisms at the electrolyte/electrode interfaces is essential for developing advanced renewable energy technologies. However, the direct probing of real-time interfacial changes, i.e., the surface intermediates, chemical environment, and electronic structure, under operating conditions is challenging and necessitates the use of in situ methods. Herein, we present a new lab-based instrument commissioned to perform in situ chemical analysis at liquid/solid interfaces using ambient pressure X-ray photoelectron spectroscopy (APXPS). This setup takes advantage of a chromium source of tender X-rays and is designed to study liquid/solid interfaces by the “dip and pull” method. Each of the main components was carefully described, and the results of performance tests are presented. Using a three-electrode setup, the system can probe the intermediate species and potential shifts across the liquid electrolyte/solid electrode interface. In addition, we demonstrate how this system allows the study of interfacial changes at gas/solid interfaces using a case study: a sodium-oxygen model battery. However, the use of APXPS in electrochemical studies is still in the early stages, so we summarize the current challenges and some developmental frontiers. Despite the challenges, we expect that joint efforts to improve instruments and the electrochemical setup will enable us to obtain a better understanding of the composition-reactivity relationship at electrochemical interfaces under realistic reaction conditions.

    Beyond the thermodynamic volcano picture in the nitrogen reduction reaction over transition-metal oxides: Implications for materials screening
    Kai S. Exner
    2022, 43 (11):  2871-2880.  DOI: 10.1016/S1872-2067(21)64025-1
    Abstract ( 184 )   HTML ( 17 )   PDF (2391KB) ( 104 )  

    Electrocatalytic production of ammonia from dinitrogen is considered as a sustainable alternative to the energy-demanding and pollutive Haber-Bosch process. A promising class of materials for selective nitrogen reduction (NRR) corresponds to transition-metal oxides given that these electrodes do not show a high activity toward the competing hydrogen evolution reaction. So far, density functional theory calculations have been used to comprehend trends in a class of materials by using the concept of scaling relations and volcano plots. This thermodynamic theory pinpoints that either the formation of the *NNH adsorbate or the formation of ammonia are reconciled with the potential-determining reaction steps. Thus, the development of NRR catalyst has largely focused on the optimization of these two elementary processes. In the present contribution, overpotential and kinetic effects are factored into the volcano plot for the NRR over transition-metal oxides by making use of the recently introduced activity descriptor Gmax(η). It is illustrated that the thermodynamic volcano picture is too simplistic as the limiting reaction step may alter close to the volcano apex: there, particularly surface reactions may govern the reaction rate. In addition, it is demonstrated how to include the formation of hydrazine as a competing side reaction into the volcano plot, which is of importance for weak binding *NNH catalysts where the formation of hydrazine may compete with the formation of ammonia. Given that the outlined methodology in this manuscript is universal and not restricted to the class of transition-metal oxides, the presented kinetic volcano picture may contribute to the development of NRR catalysts for nitrogen fixation.

    A combinatorial descriptor for volcano relationships of electrochemical nitrogen reduction reaction
    Ziyi Jiang, Youcheng Hu, Jun Huang, ShengLi Chen
    2022, 43 (11):  2881-2888.  DOI: 10.1016/S1872-2067(22)64128-7
    Abstract ( 120 )   HTML ( 5 )   PDF (1302KB) ( 87 )  
    Supporting Information

    Though touted as a potential way to realize clean ammonia synthesis, electrochemical ammonia synthesis is currently limited by its catalytic efficiency. Great effort has been made to find catalysts with improved activity toward electrochemical nitrogen reduction reaction (eNRR). Rational screening of catalysts can be facilitated using the volcano relationship between catalytic activity and adsorption energy of an intermediate, namely, the activity descriptor. In this work, we propose ΔG*NH2G*NNH as a combinatorial descriptor, which shows better predictive power than traditional descriptors using the adsorption free energies of single intermediates. The volcano plots based on the combinatorial descriptor exhibits peak activity fixedly at the descriptor value corresponding to the formation free energy of NH3, regardless of the catalyst types; while the descriptor values correspond to the top activities for eNRR on volcano plots based on single descriptors usually vary with the types of catalysts.

    Locating the cocktail and scaling-relation breaking effects of high-entropy alloy catalysts on the electrocatalytic volcano plot
    Junxiang Chen, Yaxin Ji
    2022, 43 (11):  2889-2897.  DOI: 10.1016/S1872-2067(22)64161-5
    Abstract ( 375 )   HTML ( 9 )   PDF (1238KB) ( 141 )  

    High entropy alloys (HEAs) have been the star materials in electrocatalysis research in recent years. One of their key features is the greatly increased multiplicity of active sites compared to conventional catalytic materials. This increased multiplicity stimulates a cocktail effect and a scaling-relation breaking effect, and results in improved activity. However, the multiplicity of active sites in HEAs also poses new problems for mechanistic studies. One apparent problem is the inapplicability to HEA catalysts of the currently most popular mechanistic study method, which uses the electrocatalytic theoretical framework (ETF) based on the computational hydrogen electrode (CHE). The ETF uses a single adsorption energy to represent the catalyst, i.e., a catalyst is represented by a 'point' in the volcanic relationship. It naturally does not involve the multiplicity of active sites of a catalyst, and hence loses brevity in expressing the cocktail effect and scaling-relation breaking effect in HEA catalysis. This paper attempts to solve this inapplicability. Based on the fact that the adsorption energy distribution of HEAs is close to a normal distribution, the mean and variance of the adsorption energy distribution are introduced as descriptors of the ETF, replacing the original single adsorption energy. A quantitative relationship between the variance and the cocktail and scaling-relation braking effects is established. We believe the method described in this work will make the ETF more effective in mechanistic studies of HEA electrocatalysis.

    Tunable activity of electrocatalytic CO dimerization on strained Cu surfaces: Insights from ab initio molecular dynamics simulations
    Hong Liu, Jian Liu, Bo Yang
    2022, 43 (11):  2898-2905.  DOI: 10.1016/S1872-2067(21)64044-5
    Abstract ( 141 )   HTML ( 6 )   PDF (8910KB) ( 90 )  
    Supporting Information

    Controlling catalytic activities through surface strain engineering remains a hot topic in electrocatalysis studies. Herein, ab initio molecular dynamics (AIMD) simulation associated with free energy sampling technology were performed to study the energetics of the key step of producing C2 products in electrocatalytic reduction of CO or CO2, i.e. CO dimerization, on strained Cu(100) with an explicit aqueous solvent model. It is worth mentioning that when compressive strain reaches a certain extent, the surface of Cu(100) will undergo reconstruction. We showed that, from tensile to compressive strain, the free energy barrier of CO dimerization decreased, suggesting that the activity of CO dimerization increases. It was also found that some of the reconstructed surfaces showing the lowest free energy barriers but might be less stable can be stabilized in the presence of adsorbed O or CO. Upon detailed quantitative analysis on the charges of surface Cu atoms, we found that the free energy barriers were strongly correlated with the charge of Cu atoms where the OCCO intermediate adsorbs. When the surfaces structures of Cu(100) were altered under compressive strain, the electronic structure of surface Cu atoms was monitored and thus the activity of electrocatalytic CO dimerization can be tuned.

    Two-in-one strategy to construct bifunctional oxygen electrocatalysts for rechargeable Zn-air battery
    Huibing Liu, Rixin Xie, Ziqiang Niu, Qiaohuan Jia, Liu Yang, Shitao Wang, Dapeng Cao
    2022, 43 (11):  2906-2912.  DOI: 10.1016/S1872-2067(21)63979-7
    Abstract ( 92 )   HTML ( 7 )   PDF (5327KB) ( 53 )  
    Supporting Information

    Integrating two different catalytic active sites into one composite is a useful 2-in-1 strategy for designing high-efficient bifunctional catalysts, which can easily tailor the activity of each reaction. Hence, we adopt the 2-in-1 strategy to design the metal oxyhydroxide supported on N-doped porous carbons (PA-CoFe@NPC) as the oxygen bifunctional catalyst, where NPC provides the activity for oxygen reduction reaction (ORR) while the metal oxyhydroxide is responsible for oxygen evolution reaction (OER). Results demonstrate that the PA-CoFe@NPC indeed exhibits both super ORR and OER activities. Impressively, using bifunctional PA-CoFe@NPC as the oxygen electrode, the resulting Zn-air battery exhibits outstanding charge and discharge performance with the peak power density of 156.3 mW cm‒2, and also exhibits a long-term cycle stability with continuous cyclic charge and discharge of 170 hours that is obviously better than the 20% Pt/C+IrO2 based one. The 2-in-1 strategy in this work can be efficiently extended to design other bi- or multi-functional electrocatalysts.

    Review
    Surface chemistry of MXene quantum dots: Virus mechanism-inspired mini-lab for catalysis
    Yuhua Liu, Wei Zhang, Weitao Zheng
    2022, 43 (11):  2913-2935.  DOI: 10.1016/S1872-2067(22)64167-6
    Abstract ( 84 )   HTML ( 3 )   PDF (16533KB) ( 87 )  

    Scientific research is currently more interdisciplinary. Researchers have parsed the surface structure of virus, constructed the interaction model of virus-receptors, offering the clues for studying efficient targeted drugs. Likewise, catalysis is also highly relevant to modern human life. Exploring the surface structure and physicochemical properties of catalysts is of great significance for the design of efficient catalysts. Great progresses have been made for endowing specific physicochemical properties of catalysts through controlling the size of materials and coordination chemistry of active sites, particularly at nanometer scale since Sir John Meurig Thomas and Tao Zhang’s early ground-breaking contribution, with casting on a very surface issue. Herein, functional regulation renders the emerging MXene quantum dots (MQDs) excel in contrast to the typical carbon-based quantum dots. In fact, similar to the interaction of virus-receptors model, the surface functional groups decorated MQDs provide a mini-lab to afford a variety of adjustments, involved with the type modification and electronic structure tuning of groups as well as their arrangement, together with the interaction between the groups and active materials/support, ultimately for packaging or designing high-activity catalysts.