Microstructural Regulation And Electrocatalytic Performance Of Carbon-based Transition Metal Composites

The emerging problems like environmental pollution and energy crisis have seriously threatened our daily lives.Researchers are trying their best to solve these problems from multiple perspectives.Replacing traditional fossil energy with green energy-based power generation or storage technology is one of the most efficient strategies.With the rapid development of clean energy technologies,people have higher requirements for the capacity and stability of these energy conversion and storage devices.Among them,zinc-air batteries and electrocatalytic water splitting,as typical clean energy technologies,are in urgent need of further improvement.Zinc-air batteries have gradually entered the field of research due to their high theoretical energy density and reliable safety.However,their cathode catalysts are still dominated by precious metals.High cost and limited cycle stability limit the large-scale application of zinc-air batteries.Hydrogen production by electrolysis of water is also costly due to the scarcity of catalyst materials.And it also faces problems such as low catalytic activity and stability.Therefore,it is a difficult problem to be solved to develop catalysts with low cost,catalytic activity comparable to noble metals,and high stability in this field.Based on the goal of improving the energy conversion efficiency of zinc-air batteries and electrocatalytic water splitting.We improved the performance of carbonbased transition metal composite catalysts used in three catalytic reactions.In this study,we tuned the microstructure of the catalyst and explored the factors in each catalytic reaction,which provided a basis for the subsequent design of catalysts.What we have done are described as follows:(1)The three-dimensional structure catalyst of cobalt composite nitrogen-doped carbon material was prepared through a template method.We used sodium chloride as the template to produce a hierarchical structure with rich distribution of pores.The doped-nitrogen has introduced abundant active sites into the carbon matrix material.The compounding of metals effectively prompts the oxygen evolution reaction and improves the catalytic activity,exhibiting excellent bifunctional catalytic performance.We characterized the chemical composition and structure of catalysts using XRD,Raman,XPS,etc.And we confirmed active sites in oxygen reduction and oxygen evolution reaction through acid corrosion,thiocyanate poisoning,and density functional theory calculations.(2)Preparation,electrochemical performance testing,and exploration of catalytic sites of Fe Co S/N-S-C with trifunctional catalytic activity.We employed the chemical vapor deposition method to deposit double transition metal sulfides into nitrogen-doped carbon materials.On the one hand,this is an effective way to increase the content of doping element and active sites by introducing double metals.On the other hand,we propose to enhance the oxygen evolution reaction activity with the help of the synergistic effect of bimetals.The composite with metal sulfides conducts to the hydrogen evolution reaction and realize the multifunctional application of a material.It shows superior catalytic performance and has better stability than commercial noble metal catalysts.Finally,the contribution of different metal valences to each catalytic reaction was confirmed by the methods of sulfuric acid corrosion,thiocyanate poisoning,and electrochemical in-situ reduction.