Design And Preparation Of Transition Metal-based Nanostructured Electrocatalysts And Their Application In Water Electrolysis

Regarding the ever growing problems of the rapid depletion of fossil fuels and the increasing environmental pollution,it is extremely urgent and important to develop clean and sustainable alternative energy resources.Hydrogen energy is considered as one of the most promising substitute for traditional fossil energy because of its high energy density,clean and non-pollution.Among various H2 production approachs,electrochemical splitting of water with relatively simple process is considered as one of the most promising renewable energy conversion technologies.Electrochemical water splitting can produce high-purity H2 on a large scale,it involves two simultaneous half reaction: oxygen evolution reaction（OER）at anode and hydrogen evolution reaction（HER）at cathode.Currently,platinum（Pt）and its compounds are the state-of-the-art HER electrocatalysts,while noble metal oxides（Ru O2/Ir O2）are the best OER electrocatalysts,but their high price and scarce reserves seriously limit their practical applications.Therefore,it is of great practical significance to design and develop non-noble metal-based electrocatalysts for water splitting that are cost-efficiency,abundant and highly-efficient.In this Thesis,the following high-efficiency electrocatalysts were designed from the point of view of designing highly-efficient non-noble metal electrocatalysts and regulating/modifying the morphology and structure of the catalysts to improve the intrinsic catalytic activities of the catalysts.1.Phosphorus-doped Co₃O₄ nanowire array（P-Co₃O₄/NF）supported on nickel foam was prepared by controllable P-doping technique.P-Co₃O₄/NF exhibits excellent OER and HER catalytic performance as well as superior water splitting catalytic activity and electrochemical stability.Density functional theory（DFT）calculations indicate that Pdoping can optimize the adsorption free energy for the potential determining step of the OER process and significantly improve the catalytic performance of pristine Co₃O₄.This study provides a simple and efficient method to improve the electrocatalytic performance of metal oxides by using P as dopant,and has a good reference for the electrocatalytic application of related transition metal-based materials.2.A defect-rich nitrogen doped Co₃O₄ nanoparticles embedded in nitrogen-doped carbon framework porous nanocubes（N-Co₃O₄@NC）was prepared using ZIF-67 as precursor by a controllable N-doping strategy.N-Co₃O₄@NC exhibits excellent OER electrocatalytic performance with an overpotential of only 266 m V to reach a current density of 10 m A cm-2.DFT calculations demonstrate that N-doping boosts the electrocatalytic activity of Co₃O₄ by improving the electronic conductivity,accelerating the reaction kinetics and optimizing the adsorption free energy for the potential determining step of OER.In addition,N-Co₃O₄@NC also exhibits an excellent oxygen reduction reaction（ORR）electrocatalytic activity,which enables it as a bifunctional oxygen electrode and applies in zinc-air battery.The as-assembled zinc-air battery using N-Co₃O₄@NC as air cathode demonstrates superior emergy conversion efficiency and durability,indicating the feasibility of its application in electrochemical energy conversion and storage.The results show that N doping is an effective method to improve the catalytic activity of electrocatalysts.3.NiTe₂ nanosheets array anchored on Ti mesh（Ni Te₂/TM）was prepared from Ni（OH）₂ nanosheet array via an anion exchange reaction.The as-prepared Ni Te₂/TM exhibits high OER electrocatalytic activity and superior electrochemical stability.The remarkable OER catalytic performance of Ni Te₂/TM can be attributed to its 3D porous nanoarray structure,unique metallic characteristics with excellent conductivity and high-efficiency OER active sites（Ni OOH）formed on the surface of Ni Te₂ under oxidative conditions.This work introduces an efficient and low-cost 3D OER electrocatalyst electrode,which opens up a new way to explore the transition metal telluride nanoarray for electrocatalytic applications.4.In situ growth of Ni Te nanosheet array supported on nickel foam（Ni Te/NF）was demonstrated by a facile one-step tellurization treatment by using nickel foam and Na HTe as Ni and Te sources,respectively.Benefitting from its unique metallicity and 3D nanoarray structure,Ni Te/NF shows excellent OER electrocatalytic activity.This work not only provides an efficient and low-cost nickel telluride-based OER electrocatalyst,the one-step tellurization method is expected to develop other transition metal tellurides for electrocatalytic applications.