Preparation And Electrocatalytic Properties Of Nickel-Based Nanocomposites

With the consumption of fossil fuels and the increasingly serious environmental problems,the development of new energy sources is imminent.The electrolysis of water consists of hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?,which is one of the most promising hydrogen production methods.Among them,the multi-electron,multi-step process in OER leads to slow kinetics in the process of oxygen production,which limits the further development of electrocatalytic water splitting technology.Exploring the preparation of efficient and durable OER electrocatalysts is of great significance for reducing the overpotential and improving the hydrogen production efficiency.Nickel-cobalt?nickel-iron?transition metal oxide electrode materials have attracted extensive attention as catalysts for electrocatalytic oxygen evolution due to their abundant reserves,low price and various valence changes.In this thesis,the cobalt and nickel carbonate precursor was synthesized by a stepwise co-precipitation method,and the core/shell M-NiO@Co₃O₄ nanocomposites were successfully prepared by subsequent heat trement and NaBH₄ reduction.Similarly,the nickel and iron carbonate precursor was synthesized by a stepwise co-precipitation method,and Fe-NiO/NiSe₂ hollow nanospheres were synthesized by subsequent heat trement and selenization.The morphologies and electrocatalytic oxygen evolution properties of the products were studied.The main research results are as follows:1.Unique oxygen vacancy-rich core/shell NiO@Co₃O₄ nanocomposites decorated with Co₃O₄ nanosheets were prepared as high-efficiency electrocatalyst for oxygen evolution.First,NiO@Co₃O₄ nanocomposites were prepared via a rationally-designed stepwise co-precipitation process?NiCO₃@CoCO₃ precusor?followed by controlled calcination heating treatment.With a facile NaBH₄ reduction treatment,Co₃O₄nanosheets were in situ formed on the surface of the NiO@Co₃O₄ nanocomposites,introducing more oxygen vacancies and edge sites simultaneously.This surface-restructured NiO@Co₃O₄ nanocomposites exhibited significantly-improved activity as an OER electrocatalyst,possessing a low overpotential of 293 mV at 10 mA cm^-2 and a small Tafel slope of 62 mV dec^-1.Our work provides an effective strategy to fabricate core/shell metal oxides nanocomposites with adjustable surface structures for electrocatalysis.2.Fe-doped NiO/NiSe₂ nanospheres with hollow structure were prepared for OER catalysis.First,the iron-doped nickel carbonate nanospheres precursor was prepared by stepwise co-precipitation method.Then,the precursor was calcined and selenized to obtain Fe-doped NiO/NiSe₂ nanospheres.The experiment results show that Fe-NiO/NiSe₂exhibits excellent electrocatalytic oxygen evolution activity and stability compared with Fe-NiO and NiO/NiSe2,possessing a low overpotential of 323 mV at 10 mA cm^-2 and a small Tafel slope of 67 mV dec^-1 in 1.0 mol L^-1 KOH electrolyte.The effect of iron content on the OER electrochemical performance of the catalyst was investigated.When the ratio of iron to nickel was 2:1,the catalytic performance was the best.It is a promising oxygen evolution catalyst.