Fabrication Of Three-dimensional Hierarchical Structures Based On Transition Metals For Enhanced Oxygen Evolution Catalysis

With the increasing consumption of non-renewable fossil fuel resources and the resulting environmental problems,the exploration of alternative green sustainable energy has become a hot topic.Electrolytic water reactions have become one of the most attractive ways to achieve efficient conversion and storage of energy in a chemical form.As a half-reaction in electrolytic water,the oxygen evolution reaction(OER)is kinetically sluggish and requires a high oveipotential.Precious metal oxides(i.e.,IrO2 and RuO2)have been used as high performance electrocatalysts to increase the OER reaction rate,but the disadvantages caused by the high cost and scarcity of precious metal catalysts have limited their large-scale practical applications.Therefore,it is particularly important to design OER electrocatalysts with excellent catalytic activity,durability and low cost.This article builds three-dimensional hierarchical structural electrocatalyst based on transition metal materials,effectively improves the electrochemical specific surface area,enlarges the contact area between the electrolyte and the electrode,and enhances the electron transport efficiency and conductance performance,and has excellent catalytic activity in the oxygen evolution reaction.(1)CoNiAl-LDH/NF prepared by in-situ growth method is combined with ZIF-67 nanosheets to form a three-dimensional hierar-chical structure of ZIF-67/CoNiAl-LDH/NF by crystallizing-recrystallization.Due to its porous,macroporous and mesoporous structure,it effectively increases the electrochemical active area,exposes more active components,enhances electrolyte penetration and electron transport,utilizes porous structures,and the synergistic effect between the ZIF-67 nano-array and the LDH nanosheet building block enables its excellent activity as anode material in OER.At the current density of 10 mA cm-2,the overpotential was only 303 mV,and the Tafel slope was 88 mV dec-1.(2)A novel hierarchical necklace-like CNTs @ NiCoP/C nanohybrid material was designed using a self-template method.NiCoP in the form of nanosheets and nanocages coexisting were tightly attached to CNTs.Through the introduction of carbon nanotubes and nickel,the electronic state of the metal is changed,and the synergistic and structural advantages of the components are utilized to fully expose the active sites,improve the efficiency of electron transport,and promote the diffusion of the electrolyte.CNTs @ NiCoP/C has excellent performance as an OER anode material in 1M KOH electrolyte.At a current density of 10 mA cm-2,the overpotential is only 297mV and the Tafel slope is 57.35 mV dec-1.(3)Candock-like CuO/CF prepared by in-situ nucleation method forming a three-dimensional hierarchical structure coral-like Fe-CuO/CF through FeCl2 solution with solvothermal method.The synergy between Fe and Cu effectively enhances the electrocatalytic activity and improves the charge transfer efficiency.The advantage of the porous and hollow structure formed provides more active sites and enhances the contact between the electrolyte and the electrolyte.The prepared coral-like Fe-CuO/CF was used as anode material of OER and tested in 1M KOH electrolyte.It was found that when the current density was 50mA cm-2,the overpotential was only 340mV with tafel slope of 44.28 mV dec-1.It is stable at a constant current density of 50 mA cm-2 for 8 hours due to the excellent stability.