A Tandem Catalyst Designed To Enhance Electrocatalytic Carbon Dioxide Production To Ethylene

With the advancement of industry and human society,the consumption of fossil energy such as coal,oil,and natural gas has increased year after year,and carbon dioxide（CO₂）,a result of its combustion,is emitted in vast quantities,causing the greenhouse effect.In the meantime,technologies related to clean energy have developed rapidly,wind,tide,and solar power are examples of clean renewable energy generation technologies that have been used on a wide scale.Our country possesses the world’s largest clean energy generation grid.The installed capacity of renewable energy is big and growing year after year,and overall power generation is also steadily expanding.In this context,in order to reduce global extreme weather and ecological problems induced by the greenhouse effect,as well as to make optimal use of the abundant carbon dioxide（CO₂）in the atmosphere,electrochemical carbon dioxide reduction reaction（CO₂RR）as a clean and controllable energy Conversion technology has become one of the important solutions for human society to close the carbon cycle caused by humans.CO₂RR has the advantages of electric drive generated by renewable energy,mild reaction conditions,good reaction controllability and high product energy density.Its reaction products such as methane（CH₄）,ethylene（C₂H₄）,ethane（C₂H₆）,ethanol（C₂H₅OH）.It can be directly put into social production as fuel or industrial products,and it also solves the problem of difficult storage of electric energy while consuming CO₂,and alleviates the energy crisis to a certain extent.Nonetheless,due to CO₂is a linear molecule with a relatively stable carbon-oxygen bond,it is thermodynamically stable and difficult to activate.At the same time,the process of CO₂RR reaction is accompanied by multi-step proton-electron pair transfer,resulting in diverse CO₂RR reaction pathways and complex product distribution,with products ranging from C1products（such as formate,carbon monoxide,methane,etc.）to valuable C₂₊products（such as ethylene,ethanol,etc.）,and the reaction process is accompanied by the side reaction hydrogen evolution reaction（HER）.This leads to the fact that the activity and selectivity of the catalyst in the CO₂RR process become an important factor hindering its application.Therefore,there is an urgent need to develop CO₂RR catalysts with high current density and high selectivity to high valuable C₂₊products.Metallic copper（Cu）is the unique catalyst which can convert CO₂to valuable hydrocarbon products due to its adsorption of various intermediates in the CO₂RR process.By studying the chemical state,atomic arrangement,surface structure and electronic structure of copper-based catalysts,researchers have a further understanding of the reaction mechanism of CO₂RR,but the selectivity of catalysts to high value-added C₂₊products and Current density is not ideal.Based on the above situation,the main purpose of this paper is to improve the selectivity and current density of C₂₊products.After refer to relevant literatures,it was decided to adopt the strategy of serial catalysis,that is,to complete the complex CO₂RR process through two activities.Specifically,Ag was used as the first active site to convert CO₂into CO,and the abundant CO would overflow to the surface of Cu through the interface of Cu and Ag,thereby improving the CO coverage of the Cu surface.As the second active site on Cu,there are mainly hydrogenation reaction pathways and carbon-carbon coupling reaction pathways,and the carbon-carbon coupling reaction pathway is the key step in the formation of high value-added C₂₊products.Increasing the CO coverage of Cu can increase the carbon The proportion of carbon-coupled reaction pathways,thereby increasing the selectivity of C₂₊products.The first part of this work is the preparation of Cu nanoparticles.Because carbon defects have a certain trapping effect on metal atoms under the applied voltage,we want to control the size and distribution of Cu nanoparticles by regulating the size and distribution of carbon defects.We have developed a new synthesis method to manufacture carbon defects using high current etching of carbon layers on the surface of gas diffusion layers（GDLs）,controlling both the magnitude of the applied current（I）and the time（t）of the applied current parameters to control the distribution and size of carbon defects,and then electrodeposited Cu on its surface,and finally screened out the best catalyst for C₂H₄selectivity,Cu_-0.7A-500s,when the applied voltage was-1.1（vs.RHE）,The selectivity of C₂H₄reaches 45.4%and the partial current density of C₂H₄is 94 m A cm^-2.So it has a definite catalytic activity of C₂H₄and can be used as the active center of carbon-carbon coupling of serial catalysts.The second part of this work,we proceed with the preparation of Ag nanoparticles.By means of the grope for the first part of this work,we screened out the best etching conditions,and based on this,we carried out the preparation of the second part of Ag catalysts.Firstly,the carbon layer on the surface of GDLs was etched under the optimal etching conditions,and then the distribution and morphology of Ag were regulated by changing the voltage of deposited Ag,and finally the catalyst with the best CO selectivity,Ag_0V,CO was screened out.The Faradaic efficiency of CO increases first and then decreases,and the Faradaic efficiency of CO reaches 75.8%under-1.0 V（vs.RHE）,70.7%under-1.1 V（vs.RHE）and 63.9%under-1.2 V（vs.RHE）.They all exhibit high CO selectivity in a wide range,and they can also be used as active centers for serial catalysts to generate CO.The third part of the work begins with the preparation of Cu Ag serial catalysis.We first tried to modify Ag by electrochemical replacement and electrodeposition on the Cu_0.7A-500ssynthesized in the first part of the work,but it did not achieve the expected effect of C₂H₄promotion.After that,we used the Ag_0Vsynthesized in the second part of the work as the substrate,and electrodeposited Cu on its surface,but the selectivity of CH₄increased and the selectivity of C₂H₄decreased.After inquiring about the literature,we finally used Ag_0Vas the substrate to conduct the electrodeposition of Cu by the intermediate-induced method.Making a Comparison of the Cu（26.9）synthesized by the same method,the prepared serial catalyst Cu_26.9Ag,the choice of C₂H₄The specificity increased from 44.9%to 56.2%at-1.2（vs.RHE）,the selectivity increased by 11.3%,and the partial current density of C₂H₄also increased from 113.7 m A cm^-2to 136.2 m A cm^-2.