Water Splitting Performance And Theoretical Study Of Two-dimensional NiFe Layered Double Hydroxide

Renewable fossil energy use is not only capable of causing a potential energy crisis,but also emits large amounts of CO₂greenhouse gases.In recent years,there has been an orderly push towards Carbon neutrality and Emission peak around the world in an attempt to reduce CO₂emissions.Hydrogen,as a renewable energy source,has become one of the most promising of the many green energy sources because of its advantages of efficient storage,greenness and sustainable regeneration.In addition,the use of hydrogen energy can adjust and optimize the industrial and energy structure at the root and source,and reduce CO₂emissions.Hydrogen production by electrolysis of water is an efficient and green way of producing hydrogen and consists of two half-reaction processes:the oxygen evolution reaction（OER）occurs at the anode and the hydrogen evolution reaction（HER）at the cathode.However,it still faces problems such as low catalytic performance and poor hydrogen production efficiency.In this thesis,the effect of rare earth metal element doping and photo-assisted catalysis on the catalytic performance of electrolytic water,etc.,is investigated.The details of the study are shown below.（1）Electrolysis of water can directly produce hydrogen and oxygen,providing the possibility to expand the production of high purity hydrogen.It consists of two half reactions:anodic OER and cathodic HER.Developing electrocatalysts is an effective way to improve the efficiency of water splitting.Two-dimensional Layered Double Hydroxides（LDHs）,as abundant,cheap and bifunctional catalysts,have the similar electrocatalytic performance as precious metals,thereby receiving pretty much attention.Here,a facile flash nano-precipitation（FNP）synthetic strategy is presented to acquire Ni Fe LDH.Based on it,La-Ni Fe LDH is obtained by adding rare earth element lanthanum（La）with different contents using mechanical method.Owing to the synergistic effect between La and laminate metal,La-Ni Fe LDH shows an excellent water splitting performance,where the overpotential of OER activity is 340 m V and HER performance is 57 m V at the current density of 10 m A cm^-2.Combined with characterization,performance and theoretical calculation,it is confirmed that the electronic structure of LDH laminates can be adjusted by La doping,reducing the Gibbs free energy in the reaction accordingly,which is beneficial to the water splitting reaction.In general,an easy-to-implement and rapid preparation method provides a convenient and green way to obtain water splitting catalyst with enhanced performance.（2）The technology of hydrogen production plays a hotspot with increasing demand of renewable energy,in which the combined action of water electrolysis and solar energy appears.This work has synthesized hydrangea ZnO/NiFe-LDH heterojunction by two-step hydrothermal method.It improved the range and intensity of light response,thus meet the requirement of electrocatalysis and photocatalysis in theory.The resulting ZnO/NiFe-LDH display excellent activity for electrochemical performance test with light.When used as water splitting catalyst in a full cell,the cell voltage is 1.632 V and Faradic efficiency is 99.1%.Moreover,from the in-situ Raman and DFT theory calculation results,the conclusion can be reached that the synthesized ZnO/NiFe-LDH has the property of absorbing light energy,and introduce light energy can optimize the band gap structure of the material and enhance the adsorption capacity of the group,thus significantly reduced the energy required for water splitting reaction.In sum,this work introduced a composition strategy for LDH heterojunction materials,and presented a theoretical and experimental study of the influence of light on material stricture and electrochemical reaction concept.And also believe that one important future direction of hydrogen produced is photo-assisted water splitting.