In Situ Synchrotron Radiation Study On Structure-activity Relationship Of Catalyst During The Electrochemical Reduction Reaction

In recent decades,the shortage of energy and rised content of carbon dioxide in atmosphere caused by the rapid development of industry and increased dependence on fossil fuels,which leads to serious energy and environment problems.Based on this case,renewable electric energy drived electrochemical reduction reaction of carbon dioxide reduction reaction(CO₂RR)and hydrogen evolution reaction(HER)are attractive and sustainable alternative to traditional fossil energy for large-scale utilization.Meanwhile,this strategy reduced the restrictions on raw materials,safety and environmental protection to produce a variety of organic products and hydrogen by using non-toxic,abundant and cheap greenhouse gases and water.Among this,the key to promote its commercial development lies in the reserach and application of efficient and stable electroreduction catalyst.Therefore,it is of great significance to investigate the dynamic structural change and electronic evolution through in situ characterization techniques,and further revealing the reaction mechanism and structure-activity relationship,which is very important for searching the more efficient CO₂RR and HER electrocatalyst.Therefore,we designed and synthesized various CO₂RR and HER electrocatalysts with high performance,and developed in-situ synchrotron radiation XAFS and FT-IR measurements relying on the domestic facilities(Beijing,Shanghai,Hefei and Taiwan Synchrotron Radiation Laboratory).Subsequently,we realized the in situ detection on the dynamic structural evolution,electronic optimization and intermediates adsorption/desorption process of CO₂RR catalyst under real reaction conditions,and further revealed the inherent relationship between the structure and activity.Our results provided substantial theoretical and experimental basis for the further development of efficient CO₂RR catalyst and the utilization of in situ characterization technology.This paper includes the following main research contents:1.Operando XAFS revealed the stabilized and calalystic mechanism of single atom Sn modified Cu⁺ species during the electrocatalytic CO₂RRIn this work,we prepared the surface single atom Sn modified cuprous oxide nanosheets(Sn/Cu₂O NS)through solvothermal and wet chemical method.The as-perpared Sn/Cu₂O NS exhibited the enhanced activity and selectivity of electrocatalytic conversion of CO₂ to CO.We observed the stable existence of Cu⁺ species and distinguished the key active Cu⁺ intermediates during the CO₂RR by operando XAFS and further principal component analysis(PCA),which provided the direct evidence of stable Cu⁺ species in CO₂RR.Furthermore,operando SRFT-IR and theoretical calculation investigated the stabilization mechanism of Cu⁺ species and subsurface O atoms on Cu₂O nanosheets by single-atom Sn modifying,and revealed the adsorption and activation process of intermediates in CO₂RR.This work provided a new strategy for design and optimization of Cu-based CO₂RR catalysts with high stability and activity.2.In situ investigation of structure-activity relationship on coordination unsaturated Ni single atom catalyst for electrochemical CO₂RRWe synthesized the single atom Ni supported on metal organic framework(MOF)catalysts(Ni/N-C)with uniform dispersion and active sites by successfully wet chemical method.The electrochemical CO₂RR measurements showed that the Ni/N-C catalyst exhibited a hige FEco of 93.8%,and still kept more than 90%even at a high current density of 100 mA/cm2.The morphology and structure characterization found that the coordination environment of supported Ni single atom was unsaturated Ni-N3 structure.Moreover,the in situ XAFS measurement confirmed that the coordination unsaturated Ni-N3 single site has the lower valence and stronger reducibility.Then,in situ FT-IR results revealed that the unsaturated Ni-N3 active site had optimized adsorption and activation ability for the intermediates of CO product,thus improving the selectivity and activity of CO₂-to-CO conversion.Our results provide theoretical and experimental basis for enhancing the CO₂RR performance of single atom catalyst by regulating the coordination environment.3.Dynamic structural evolution of Co-WSe₂ nanosheets in electrocatalytic HER revealed by in situ XAFSWe used the element doping strategy to introduce the Co atoms(Co-WSe₂ NS)into tungsten diselenide nanosheets through one-step hydrothermal method,and investigated the element doping effect of Co atoms by in-situ XAFS.The XPS and UPS results showed that the doped Co atoms enhanced the conductivity and electron transport ability of the substrated WSe₂ NS,which further improving the catalytic performance of Co-WSe₂ NS.Moreover,in situ synchrotron radiation XAFS measurements showed that the Se active sites of Co-WSe₂ NS had a dynamic and reversible structural evolution during the HER.At the same time,DFT calculation verified the rationality of this structural evolution,and proved that the spontaneous structural evolution optimized the electronic structure and activation energy for H+of Se active sites,which led to the improvement of catalytic activity,which provided a new understanding for using the element doping strategy to regulate the substrate performance.