Design And Preparation Of High Efficiency Electrocatalytic Anode Material Based On Ni-Based LDHs

With the rapid development of modern society,the demand for energy is gradually increasing.However,the rapid consumption of non-renewable energy and the environmental pollution caused by it prompt people to explore efficient and green new energy.As a new type of green energy,hydrogen energy has the characteristics of high energy density,no pollution and renewable.It has been widely used in aerospace,transportation and other fields,and has been paid attention by the country and society.Hydrogen production from water electrolysis has been widely studied and concerned in recent years because of its advantages of low cost and high energy utilization efficiency.Electrolytic water contains two half reactions,namely oxygen evolution reaction(OER)and hydrogen evolution reaction(HER).Hydrogen and oxygen are generated through HER and OER respectively.However,the four-electron transfer process involved in OER causes slow reaction kinetics,which leads to the working potential is far greater than the theoretical value in actual production.Besides,ruthenium(Ru),iridium(Ir)and other precious metals are still the main materials for commercial electrode materials.The high price and limited reserves of precious metals hinder their large-scale industrial application.According to the above problems in water electrolysis:on the one hand,for the reaction itself,direct optimization of OER process coupled with HER is one of the research directions.At the same time,many studies substitute OER through other oxidation reactions such as HMFOR and have achieved very good results.On the other hand,in view of the problem in electrode materials,Ni base of layered double hydroxides(LDHs)as a kind of electrode materials with abundant reserves and low price,because of its special nanosheet structure,efficient catalytic activity and good ion exchange rates,is expected to replace precious metal materials,has been widely research and attention.Based on the above,it is of great scientific value to study the Ni-based LDHs electrode material for the oxidation reaction coupled with HER.However,the electrical conductivity of LDHs materials limits its application in the field of electrocatalysis.Moreover,the adsorption of reactants in OER and HMFOR on the electrode surface often has a certain potential barrier,which has an adverse effect on the reaction.Hence,there is still a great space to explore how to design and prepare new catalysts by utilizing the characteristics of LDHs materials reasonably and combining with materials with strong selective adsorption capacity.Therefore,this thesis starts with the strategy of material composite,using LDHs flake morphology for material load,promote the adsorption of reactants,effectively improve the catalytic activity of LDHs material.The detailed contents of this paper are as follows:In chapter 1,the electrocatalytic oxygen evolution reaction and electrocatalytic HMF oxidation reaction are described in detail,and the basic process and mechanism of the above reactions are introduced.Subsequently,the structure,properties and synthesis methods of LDHs are systematically introduced.The modulation methods and research progress of LDHs materials in OER and HMFOR are reported and summarized.Finally,through analyzing the current research progress,the research idea and main research content of this thesis are put forward.In chapter 2,based on the adsorption and activation ability of material composites,a new type of NiCoP-CeO2 composite material was prepared by simple hydrothermal method and high-temperature phosphating strategy,using NiCo-LDHs as precursor and nickel foam as substrate.Its catalytic performance,crystal structure,microstructure,hydrophilicity and so on were systematically tested and characterized.In OER tests,we found that the NiCoP-CeO2 composite showed excellent performance compared to the pure NiCoP,with a low overpotential of 217 mV and Tafel slope of 45 mV dec-1 at a current density of 10 mA cm-2.The results show that CeO2 has a certain limiting effect on NiCo-LDHs,which maintains the morphology of NiCo-LDHs nanosheets,and is conducive to good contact with water and exposure of active sites.In addition,when CeO2 is loaded onto NiCoP,the hydrophilicity of the catalyst is significantly enhanced,which ultimately improves the catalytic capacity of the material.This work also provides an ingenious synthesis strategy for the preparation of efficient and cheap electrocatalytic materials.In chapter 3,the Pt/NiFe-LDHs composite was designed and synthesized by simple hydrothermal and chemical reduction methods combining with the lamellar morphology of LDHs material and high catalytic activity of Pt.The HMFOR properties,crystal structure,morphology,element proportion and the adsorption properties of HMF were characterized and analyzed.The results show that at 1.45 V electrode voltage(vs.RHE),the current density of Pt/NiFe-LDHs composite is 3 times higher than that of the simple NiFe-LDHs,and the current density of Pt/NiFe-LDHs composite is 6 times higher than that of its OER performance.It is found that the Pt is evenly distributed due to the lamellar morphology of LDHs.At the same time,the active site of the material was significantly increased with the help of the adsorption capacity of Pt to HMF,which lead to the catalytic capacity was improved.In this work,HMFOR was used instead of OER to reduce the overpotential of electrolytic water,and the catalytic capacity was further improved by enhancing adsorption ability.At the same time,some exploration and research were carried out on HMFOR.In chapter 4,the research significance,research content and innovation points of this thesis are summarized.At the same time,combined with the work content,the deficiencies of the present stage are analyzed,the existing problems are put forward further plans,and the next work is prospected.