Metal-doped Spinel NiCo₂O₄ For Electrocatalytic Water Oxidation

Oxygen evolution reaction（OER）plays a crucial role in electrochemical energy storage and conversion technologies such as water electrolysis for hydrogen production,carbon dioxide electroreduction and metal-air batteries,but its overpotential is large and kinetics are slow.Therfore,a catalyst is required to speed up the reaction rate.Currently,Ru/Ir-based oxide catalysts are recognized as the best performing OER catalysts in the acidic systems.However,the high price and natural scarcity of noble metal ruthenium/iridium limit their large-scale applications.Therefore,the development of efficient,stable and non-precious metal catalysts for OER in basic media has become a current research focus.Among many non-precious metal oxygen evolution catalysts,NiCo₂O₄ spinel has attracted much attention due to its environmental friendliness,low price,simple preparation,and abundant redox couples.However,pure NiCo₂O₄ spinel has low OER activity.How to improve its catalytic performance is the goal of the research.Based on this,in this paper,the electrocatalytic oxygen evolution activity was improved by doping with the metal element and regulating the morphology.The main research contents and results are as follows:（1）The x W-NiCo₂O₄ catalysts with different amounts of W doping were synthesized by a two-step solvothermal and calcination method.The characterization results showed that the prepared x W-NiCo₂O₄ samples exhibited porous structure.The electrocatalytic OER performance of NiCo₂O₄ samples with different doping amounts of tungsten was tested.The results showed that the electrocatalytic activity was the best when the doping amount of tungsten was 10%,and the overpotential was 327 m V at a current density of 10 m A cm^-2.Compared with the pure NiCo₂O₄ catalyst,the overpotential of 10%W-NiCo₂O₄reduced by 57 m V;and the 10%W-NiCo₂O₄ catalyst can be maintained 90 hours at a current density of 10 m A cm^-2 without significant change in potential.（2）NiCo₂O₄ mesoporous nanosheet catalysts and a series of Fe_xNi_1-xCo₂O₄（x=0,0.1,0.2,0.3 and 0.4）samples with different Fe doping amounts were prepared by a combination of hydrothermal and calcination methods.The research shows that the introduction of Fe can promote the pre-oxidation of Co/Ni to accelerate the generation of OER active species.The Raman spectroscopy results also show that the active species in the OER process for the pure NiCo₂O₄ sample is NiCo₂O₄ itself,while for the Fe-doped sample,its active species is Ni（Co）OOH,and it is concluded that the introduction of Fe is beneficial to promote the transformation of the spinel phase into Ni（Co）OOH active species during the OER process.Benefiting from the generation of Ni（Co）OOH active species and the special mesoporous nanosheet structure,the optimized Fe_0.2Ni_0.8Co₂O₄ sample exhibits the best catalytic activity.When the current density is 10 m A cm^-2,the overpotential of the Fe_0.2Ni_0.8Co₂O₄ sample was 270 m V and the Tafel slope was 39 m V dec^-1 in 1 M KOH solution.This thesis provides a method for the preparation of mesoporous nanosheet spinel oxides and proposes strategies to facilitate the transformation of metal oxides into active species during the OER process.