Construction Of Nickel Iron Double Hydroxide Core-shell Structure And Study Of Their Electrocatalytic Oxygen Evolution Reaction

The active development of renewable energy helps reduce people’s dependence on traditional fossil energy and build an environmentally friendly society.Hydrogen production from electrolytic water is an effective way to solve the problem of rapid consumption of fossil fuel resources and global warming.The key to its success is to design an efficient,stable and reliable electro-catalyst for oxygen evolution reaction（OER）.Oxygen evolution reaction involves multiple steps of proton coupling and complex four-electron transfer process.The slow reaction kinetics eventually leads to a large overpotential triggering the oxygen evolution reaction,which is the key factor limiting the efficiency of water electrolysis.Therefore,the key to successful hydrogen production from electrolytic water is the design of a high-quality electrocatalyst for the oxygen precipitation reaction that has an efficient conversion rate and reliable stability.To date,the most effective catalysts for OER have been found to be noble metal oxides,such as Ir O₂and Ru O₂,because they significantly reduce overpotential OER requirements.However,precious metals are expensive and rare,which limits their widespread use as efficient electrocatalysts in practical industries.Among many non-precious metal electrocatalysts,NiFe LDH shows excellent oxygen evolution activity under alkaline electrolyte conditions.However,the poor electron transfer ability of NiFe LDH prevents the active site from being fully utilized.In order to improve this deficiency,this paper found a feasible method to disperse NiFe LDH as a secondary structure onto the nano-array constructed on a single electrode.Non-metallic atom doping has been widely studied day by day,which is conducive to regulating the electronic structure of catalytic materials and improving the performance of electrocatalysts.In this paper,we further improve the oxygen evolution ability of electrocatalysts by doping non-metallic atoms.The specific research contents are as follows:（1）NiMoO₄nanorods were uniformly and densely grown on foam nickel by hydrothermal method（denoted as NiMoO₄）.NiMoO₄nanorods were doped with S by secondary hydrothermal method（denoted as S-NiMoO₄）.Finally,NiFe LDH was grown on nanorods by constant voltage electrodeposition,using Ni²⁺and Fe³⁺solution as electrolyte,to prepare three-dimensional core-shell structure NiFe LDH@S-NiMoO₄.The structure characterization and electrocatalytic oxygen evolution performance test of the experimental samples showed that the prepared catalyst electrode showed excellent OER electrocatalytic performance in 1M KOH solution.The overpotential of the composite NiFe LDH@S-NiMoO₄is only 277 m V with a Tafel slope of 78 m V dec^-1at a current density of 100 m A cm^-2and has good stability and durability.The research shows that the electrodeposition time can affect the thickness of the NiFe LDH layer.The gradually thickened nanolayer can increase the specific surface area and provide more active centers,but the thicker NiFe LDH will cover the active sites on the nanorods,hinder the transmission of electrons,and make the improvement of the electrocatalytic performance less useful.（2）On the basis of the preparation of NiMoO₄nanorods,the NiMoO₄nanorods were P doped by low temperature phosphating（denoted as P-NiMoO₄）.Finally,the same electrodeposition method of Chapter Three was used to find the optimal time for electrodeposition by using a solution containing Ni²⁺and Fe³⁺as the electrolyte to grow NiFe LDH on nanorods and prepare the three-dimensional core-shell structure NiFe LDH@P-NiMoO₄.The overpotential of the composite NiFe LDH@P-NiMoO₄was only267 m V and the Tafel slope of 93 m V dec^-1at a current density of 100 m A cm^-2in 1 M KOH solution and exhibited good stability and durability.Obviously,this work provides a new strategy for the construction of OER electrocatalysts made of non-precious metals with excellent OER catalytic performance and good stability.