Studies On The Surface Reconstruction Of Copper-based Catalysts By Electrochemical Tuning And Its Influence To Water Electrolysis

Hydrogen production by electrolysis of water is considered to be one of the most promising methods to solve the problems of energy shortage,environmental pollution and global warming due to its mature technology,simple operation and high purity of hydrogen production.Since the slow oxygen evolution reaction kinetics restricts the efficiency of hydrogen production from electrolyzed water,it is urgent to develop low-cost,earth-abundant and efficient electrocatalysts to reduce the reaction energy barrier and improve the efficiency of hydrogen production from electrolyzed water.Transition metal-based catalysts have the characteristics of abundant reserves,high catalytic activity and flexible and adjustable electronic structure,which make them candidates for electrolytic water catalysts.However,it has been found that most of the catalysts are structurally unstable under strong base and high voltage conditions,and reconstruction occurs.Compared with the initial catalyst（pre-catalyst）,the active species formed in situ after reconstruction generally have the advantages of richer active sites,lower activation energy barrier and higher conductivity.Therefore,in-depth exploration of the structural evolution of pre-catalysts has important guiding significance for designing and optimizing catalysts with ideal performance.Based on this,three high-efficiency copper-based pre-catalysts,anti-perovskite-metal oxide composites,metal-organic framework materials（MOF）and prussian blue analogues materials（PBA）,were designed to explore their structural evolution in the catalytic process and investigate their corresponding hydrogen evolution reaction（HER）,oxygen evolution reaction（OER）and total water splitting performance.The main contents are as follows:（1）(Fe_1-xCu_x)₄N-Cu₂O heterostructures were synthesized on copper foam by KCl salt-assisted solution combustion method.The interaction between(Fe_1-xCu_x)₄N and Cu₂O in the form of p-n junction effectively promotes charge transfer,thereby effectively improving the reaction kinetics and increasing the active sites.At the same time,(Fe_1-xCu_x)₄N-Cu₂O/CF undergoes different structural evolution during HER and OER processes,and is reconstructed into Fe-Cu₂O and FeOOH-CuO,respectively.The reconstructed species has the best intermediate adsorption free energy,and the overpotentials of HER and OER are only 30 and 307 mV at a current density of 10mA·cm^-2in 1.0 M KOH electrolyte.The electrolytic cell assembled with the reconstructed catalyst achieved overall water splitting of 1.57 V@10 mA·cm^-2 and Faraday efficiency（FE）of nearly 100%.（2）With imidazole-4,5-dicarboxylic acid as ligand,Cu-MOF was prepared in situ on CF by electrochemical deposition.Through CV electrochemical activation strategy,Cu-MOF was reconstructed,the active sites are increased,and the catalytic activity was enhanced.The Cu-MOF was finally reconstructed into high porosity sheet-like CuO（OER）and popcorn-like Cu₂O（HER）.The overpotentials of OER and HER were 158mV and 288 mV at a current density of 10 mA·cm^-2 in 1.0 M KOH electrolyte.The electrolytic cell assembled with the reconstructed catalyst achieved overall water splitting of 1.568 V@10 mA·cm^-2 and FE up to 95%.（3）With copper nitrate and potassium hexacyanocobaltate（III）as raw materials,CoCu-PBA/CF was synthesized on CF by co-precipitation method.The rate and degree of CoCu-PBA/CF reconstruction were investigated by CV electrochemical activation.The PBA reconstruction rate can be regulated by Cu²⁺.The slower the reconstruction rate,the smaller the size of the active species formed in situ and the higher the catalytic activity.It was confirmed that the more thorough the reconstruction of CuCo-PBA,the better the catalytic activity.PBA was finally completely reconstructed into Cu@CoO_xcore-shell microspheres（HER）and CuO nanosheets（OER）.HER and OER only required 131 and 269 mV to reach a current density of 10 mA·cm^-2 in 1.0 M KOH electrolyte.The electrolytic cell assembled with the reconstructed catalyst achieved overall water splitting of 1.57 V@10 mA·cm^-2 and FE up to 95%.