Synthesis Of NiFe₂O₄-NiOOH/Ni Foam Via In Situ Electrochemical Transformation And Their Oxygen Evolution Reaction Performance

Sharp consume of fossil energy has resulted in the energy shortage and environment pollution,which spurs researchers on hunting for renewable,clean and low-cost energy alternatives.Developing hydrogen as the substitution is effective strategy to solve the problems.Electrochemical water splitting is one of the important ways to efficiently produce hydrogen with high purity.However,as the other half reaction of water splitting,oxygen evolution reaction?OER?with the sluggish kinetics always dissipates excess energy and lowers the overall efficiency of the electrolysis,resulting in urgent need of high performance electrocatalysts to promote the oxygen evolution reaction.The noble metal oxides?for example RuO₂ and IrO₂?show excellent OER activity,but inevitably limited by their scarcity and consequently high cost.As for the activity and stability under large current density,they are far from the ideal OER electrocatalysts.Hence researches constantly pursue low-cost,earth-abundant materials with high efficiency and long-time stability maintained at high current density.The NiFe-based compounds are cheap and easily available,but there's still a long distance from industrial applications.Our research methods in this thesis are:first,choosing the Ni foam?NF?as the substrate,building the self-support structure to accelerate electronic transmission,accordingly improve the electrical conductivity of the material;second,constructing heterostructure to adjust the electronic structure for increasing the catalytic activity;third,aerophobic surface of nanosheet is beneficial to accelerate the departure of gas,accordingly keep stability at large current.we obtain high OER activity and better stability Ni Fe₂O₄-NiOOH/NF by in situ electrochemical conversion.The main work in this dissertation is:Here,an in-situ transformation of OER active NiFe₂O₄-NiOOH nanosheet array is demonstrated as a highly efficient OER electrocatalyst by the anodization of Fe₂O₃domains anchored on Ni?OH?₂ nanosheet array.In situ potential-dependent Raman spectroscopy reveals the process.The as-converted high efficient heterogeneous products can deliver the current density of 30 mA cm^-2 with the small overpotential of240 mV,and only requires an overpotential of 410 mV to achieve an amazing huge current density of 3000 mA cm^-2.Also,the NiFe₂O_4-NiOOH can maintain the current density of⁸0 mA cm^-2 for more than 100 h.It is found that the synergistical effect of the in situ formed NiFe₂O₄ and amorphous NiOOH as well as the hydrophilic and aerophobic electrode surface make main contribution to the outstanding OER activity of the catalyst.This work will bring new perspectives to the recognition of the origin of the NiFe compounds for OER and provide a mild method to synthesize amorphous spinel materials at room temperature.