Surface And Interface Design Of Cobalt-based Self-supporting Catalyst For Hydrogen Evolution And Oxygen Evolution Reaction

The increasing energy crisis has forced mankind to explore clean energy that can replace fossil fuels.The application of renewable clean energies（such as solar energy,wind energy）is limited by their intermittent or regional restrictions.In order to avoid these problems,the above unstable clean energies can be used to prepare stable hydrogen energy.Hydrogen energy is also widely concerned because of its high calorific value,and its clean combustion product.Electrolyzing water is considered to be the most convenient and clean way to produce hydrogen.However,electrolyzing water is a strong uphill reaction.The working voltage of the electrolytic cell is 1.8～2.0V generally,which is much larger than the theoretical limit voltage of 1.23 V.Therefore,a highly efficient electrolytic water catalyst is urgently needed to improve its reaction kinetics and reduce the working voltage of electrolytic cell.So far,precious metal-based electrocatalysts are still the best catalytic materials for electrolyzing water,but the scarcity and high price of them limit their wide application.Therefore,the development of electrolyzed water catalytic materials with abundant reserves,low prices,easy preparation,and good catalytic performance has become a key point in this research field.Based on the research achievements of electrolysis water catalysts in recent years,this paper mainly focus on improving the electocatalytic performance of transition metal-based electrolysis water materials,and developing self-supporting electrodes by in-situ growth on a conductive substrate,adjusting the material composition,microstructure and surface state of electrocatalysts.The main research contents are as follows:1.Hierarchical growth of vertically standing Fe3O4-FeSe/CoSe2 nano-array for high effective oxygen evolution reactionThe slow oxygen evolution reaction（OER）kinetics hinders the large-scale application of electrolyzed water.This work reported a Fe₃O₄-FeSe/CoSe₂ nano-array structured material grown vertically on carbon cloth as a highly active OER self-supporting catalyst.The experimental results show that the introduction of Fe element will have a significant effect on the micro-morphology,electronic structure and electrocatalytic oxygen evolution performance of CoSe₂.It found that under hydrothermal conditions,a competitive reaction will occur between Fe and Co,and rock-like Fe₃O₄ particles will preferentially grow on the carbon cloth,so that the CoSe₂nanoarray is more firmly fixed in carbon cloth to improve the stability of the catalyst.At the same time,a small amount of FeSe doped or adsorbed on the CoSe₂ array.XPS results suggested that the Fe and Co multicomponents can mutually adjust their electronic structure,and the synergistic advantage between Fe₃O₄-FeSe and CoSe₂ make the OER performance of Fe₃O₄-FeSe/CoSe₂far better than that of pure CoSe₂.It achieves a low overpotential of 279 m V at a current density of 10 m A cm^-2 and has68.78 m V dec^-1 low Tafel slope.This work exhibited a new structure of high-efficiency OER electrocatalysts,a nano-array hierarchical structure of Fe₃O₄-FeSe/CoSe₂ fixed on carbon cloth.2.Puzzle-inspired carbon dots coupled with cobalt phosphide for constructing a highly-effective overall water splitting interfaceAlthough a vertically standing nano-array is prepared in our previous work,but it is still too compact and large,which cannot expose enough catalytic active for enhancing its electrocatalytical performance.In this work,we are inspired by jigsaw puzzles to combine carbon dots（CDs）with rich negatively charged functional groups and Co²⁺through electrostatic interaction,and then phosphatize it to obtain bamboo-like CDs/CoP nano-arrays.The experimental results showed that the combination of nitrogen-doped carbon dots and CoP nanoparticles can effectively prevent the agglomeration of CoP,thereby helping to expose more catalytically active sites.The cavities and porous walls of the slub-shaped CDs/CoP nano-arrays can promote the transport of protons/electrons on the surface of the electrocatalyst and accelerate the desorption of reaction products.The electronic interaction between CDs and CoP can enhance their synergy and accelerate the kinetics of the electrolyzed water reaction at the catalytic interface to achieve efficient electrochemical water splitting.The positive and negative charge combination strategy inspired by the jigsaw puzzle provides a simple and effective method for constructing more nanocomposites.3.Modifying surface Co Foam by Noble Platinum to Boost its Electrocatalytic Hydrogen Evolution PerformanceThe electrocatalytic performance of the materials obtained in the previous work is still inferior to the precious metal Pt.Therefore,we weigh the cost and performance and consider using trace amounts of precious metals to improve the electrocatalytic hydrogen evolution performance of non-precious metal materials.According to the principle of different metal activity sequences to design experiment,limit the amount of chloroplatinic acid only can cover monoatomic layer Pt on Co foam maximally,and soak Co foam in a dilute chloroplatinic acid solution for different times,and trace Pt was modified on the Co foam through the replacement reaction.The experimental results show that trace Pt modification can significantly improve the hydrogen evolution performance of the catalyst.The peak overpotential of Co Foam-Pt-2 h is almost close to that of commercial Pt/C.In addition,Co Foam/MXene-Pt-2 h co-modified with MXene and Pt requires only an overpotential of-55.6 m V at a current density of 10 m A cm^-2,which is even lower than the commercialized Pt/C（-106.6 mV）.