MOFs Derived Delafossite CuCoO₂ Nanocrystals And Its Application In Oxygen Evolution Reaction

The development of efficient,stable,and low-cost oxygen evolution reaction（OER） catalysts has been a research hotspot in the field of electrolyzed water.Among the many non-noble metal OER catalysts,delafossite ABO₂ is characterized by its open structure space,abundant active sites,and controllable electronic structure,and that’s what makes it so important in electrocatalysis.Theoretical calculation shows that CuCoO₂ has the highest activity in electrolytic water OER in Cu-based ABO₂.However,when CuCoO₂is prepared by conventional solid-state reaction at high temperature and ion exchange method,because of the high phase temperature and long reaction time,the CuCoO₂nanocrystal materials with ideal size cannot be obtained.In this paper,the preparation of nanostructured CuCoO₂ by metal source-assisted solvothermal method with MOFs as the breakthrough,taking advantage of the inherent characteristics of MOFs,such as controllable morphology,adjustable pore size,easy modification,and functionalization.Based on the optimization of the solvothermal process,the micro-morphology,electronic structure,and surface defects of a series of CuCoO₂ materials were designed and controlled to optimize the performance of OER.The research work in this paper provides a new strategy for the rational design of MOFs derivatives as efficient OER catalysts for water splitting and a new research direction for the synthesis of delafossite oxides.In this work,the pure-phase CuCoO₂ was synthesized by the solvothermal method in three routes.In the first route,using Cu-BTC as the Cu source and Co（NO₃）₂·6H₂O as the Co source,the hexagon-shaped CCO1 was prepared by adjusting the reaction solvent,Na OH content,and precursor composition.In the second route,Cu（NO₃）₂·3H₂O was used as Cu source and ZIF-67 was used as Co source.By adjusting the amount of ethylene glycol,the type of reductant,the amount of Na OH,and the concentration parameters of reactants,six square sheets of CCO2 were successfully synthesized.In the third route,using Cu-BTC as the Cu source and ZIF-67 as the Co source,the solvothermal process was systematically optimized by adjusting the reaction solvent,reaction temperature,precursor component,and Na OH content,CCO3nanocrystals were obtained.XRD,SEM,BET,TEM,and XPS were used for the physical characterization.In 1.0 M KOH alkaline electrolyte,the OER catalytic activity of MOFs derived CuCoO₂ working electrode was investigated by cyclic voltammetry（CV）,electrochemical impedance spectroscopy（EIS）,and chronoamperometry（CP）,and its OER mechanism was discussed.The results showed that the OER catalytic activity of the nickel foam loaded with MOFs derived CuCoO₂ powders was higher than that of the bare nickel.Compared to Ni@CCO1(η₁₀=407.6 m V,Tafel slope=88.1 m V dec^-1)and Ni@CCO2(η₁₀=394.5 m V,Tafel slope=82.6 m V dec^-1)electrodes,the OER performance of Ni@CCO3-5g electrode is the best,require an overpotential of 364.7m V to reach 10 m A cm^-2,and the Tafel slope is 64.1 m V dec^-1.The XPS results showed that the higher catalytic efficiency of CCO3 nanocrystals could be due to the oxygen vacancy caused by lattice oxygen loss,the increase of OH^-content on the surface,and the synergistic effect of Cu²⁺/Cu⁺and Co²⁺/Co³⁺redox pairs.