Fabrication Of Nanoporous Gold,Tin Catalysts For Electrochemical Reduction Of Carbon Dioxide

The energy and environmental problems have always been accompanied by development of science and technology.The greenhouse effect caused by excessive CO₂ emissions seriously endangers the living environment of human beings.Driven by renewable energy,CO₂electroreduction closing the carbon cycle and producing high value-added chemicals is an effective means to solve the energy crisis and global warming.However,CO₂ electroreduction still faces the following problems:?1?the activity of catalysts is limited;?2?the reaction mechanism is complex and needs to be further revealed;?3?the relationship between the structure of catalysts and reaction performance is ambiguous.Doping,atomic vacancies,grain boundaries and other defective catalysts,whose surface structure can change the adsorption behavior and chemical activity of the catalysts,selectively improve the stability of specific intermediates and facilitate the electrocatalytic reaction,have attracted extensive attention of researchers.Residual stress and plastic deformation occur during the preparation of nanoporous metals during de-alloying.Therefore,a large number of crystal defects?such as dislocations,twins and stacking faults?are produced.The structure of nanoporous metal is often composed of complex curvature surfaces,i.e.abundant steps,twists and plan sites,which are conducive to catalytic reaction.Hence,we prepared nanoporous gold and nanoporous Sn/SnO₂ surface composite catalysts,and their structure and morphology were characterized and analyzed in detail in order to understand the structure-activity relationship between the structure and performance of nanoporous catalysts accurately.Specific research contents are as follows:?1?Nanoporous gold?NPG?with three-dimensional bicontinuous pore-ligament network structure was prepared by facile de-alloying method.We accurately characterized the surface atomic structure of its surface.The DFT calculation is used to judge the degree of difficulty of various of coordination environment atoms for producing CO.From the experiment,the Faraday efficiency of porous gold with a large number of low coordination surface atoms and gold octahedron with?111?crystal surface were compared.Both theoretical and experimental results show that gold atoms with low coordination environment can promote the electroreduction of carbon dioxide to carbon monoxide.?2?Nanoporous Sn/SnO₂?np-Sn/SnO₂?composite electrocatalysts were prepared by two-step de-alloying.Compared with the porous Sn catalyst obtained by one-step dealloying,the specific surface area and electrochemical active area of np-Sn/SnO₂ composite electrocatalysts were further improved.At the same time,due to the existence of high-density grain boundaries,the catalytic active sites of the composite catalysts also increased.Therefore,np-Sn/SnO₂composite catalyst exhibits excellent performance of CO₂RR.Compared with the porous Sn electrode,the electrode can achieve higher Faraday efficiency of formic acid in a wide potential range,and its Faraday efficiency of formic acid is higher than 70%.In addition,the composite catalyst exhibited good electrocatalytic stability,i.e.the current density and Faraday efficiency of formic acid did not decrease significantly at-0.8 V?relative to reversible hydrogen reference electrode?for up to 58 hours.