| Transition metal group elements are not only abundant,cheap and environmentally friendly in the earth,but also have the advantages of diverse crystal structure and adjustable valence state.This makes it shows outstanding property in the fields of photocatalysis,electrocatalysis,supercapacitors and pollutant degradation.With the development of scientific research,transition metals are also being studied more intensively.In general,catalysts with a specific nanomaterial structure have a larger surface area to expose more active sites,and the morphology is controllable.Therefore,the design of transition metal based electrocatalysts with specific nanostructures has become a focus of catalytic materials research.In recent years,energy crisis and environmental problems are the two major challenges.In order to realize the sustainable development of human’s production and life,the development of green renewable energy to replace ancient fossil fuels which has become a research hotspot.Hydrogen is recognized as the main energy carrier to replace fossil energy,because of its high combustion heat density and zero carbon emission.It is an effective mean to solve the two problems.As an effective way to produce hydrogen in industry,electrocatalytic water decomposition technology provides an important contribution to obtain green hydrogen energy and change air pollution.However,the electrocatalytic water decomposition process contains two half reactions,namely oxygen evolution reaction(OER)and hydrogen evolution reaction(HER).The oxygen evolution reaction involves multi-step proton coupling electron and numerous side reactions.That leads to high thermodynamic reaction barrier and slow kinetic reaction process,which seriously hinders the rate of hydrogen production from water decomposition and consumes a lot of energy.The use of electrocatalysts can significantly reduce the reaction barrier during electrocatalysis progress.Pt and Ru/Ir electrodes are the best HER and OER electrocatalysts,respectively.However,these electrocatalyst electrodes are severely hindered due to the scarcity and high price of precious metals for the large-scale production and application.As a transition metal element,cobalt is relatively rich in earth,and Co3O4 as a spinel material has a variety of crystal structures and electronic valence states,so it is a kind of electrocatalyst material with great potential.However,Co3O4 material is greatly limited in the field of electrocatalysis due to its shortcomings of poor conductivity and insufficient active sites.In this paper,the electrocatalytic performance of Co3O4 material was optimized by means of morphological regulation,increasing specific surface area,increasing active site,and constructing heterogeneous structure to form internal electric field,etc.Through analyzing its structure and electrochemical properties,the mechanism of catalytic activity was studied for the synthesized catalyst.The specific research content is as follows:In Chapter 1,the mechanism and evaluation index of water decomposition were systematically described.We have also analyzed the types and applications of common electrocatalyst materials.There were existing many problems of electrocatalysts in industrial water decomposition.The transition metal cobalt electrocatalyst compounds were emphatically introduced for the types and research progress,and the solutions of the core problems were proposed.Finally,the method of preparing new catalysts with high efficiency and stability by morphology and structure control was summarized.Meanwhile,the topic content and research significance of this paper are introduced.In Chapter 2,several Co3O4 materials with different micromorphology were synthesized by different preparation methods,and they were combined with titanium mesh(TM)conductive substrate which was resistant acid-alkali corrosion.The preparation methods were introduced,and then we characterized the crystal structures of Co3O4 materials.The electrocatalytic properties of various materials were compared by electrocatalytic tests,and the mechanism was analyzed for improving the performance of OER.At the same time,we pointed out the existing problems and the solution ideas for Co3O4 in the field of electrocatalytic water decomposition.In Chapter 3,we modified the Co3O4 nano wire electrocatalyst by phosphatizing progress at low temperature,thus,CoP/Co3O4 heterojunction was in situ constructed and its crystal structure was characterized.And then we have tested the electrochemical properties of CoP/Co3O4 and analyzed the mechanism for the activity enhancement of OER.The results showed that,from the micro morphology,the morphology of nanowires not only facilitated the diffusion of electrolyte ions,but also facilitated the rapid separation of product gas.From the composition,inorganic nonmetallic P element changed the distribution of electron cloud around Co,which not only improved the conductivity of the catalyst,but also increased the number of active species for cobalt,and improved the catalytic activity of the catalyst.From the structures,on the one hand,the strong coupling inductance effect of the in-situ heterostructure not only improved the proton transmission speed,but also was beneficial to improve the conductivity of the catalyst.On the other hand,it solved the problem that the heterogeneous material was easy to be peeled off in experiment,which greatly increased the service life of the heterogeneous structure.Therefore,it showed excellent catalytic activity and stability in the process of OER,HER and overall water splitting.In the fourth chapter,the paper was summarized and the main innovation points of this paper were pointed out.In view of the shortage of electrocatalytic materials for water decomposition,we proposed a planned solution and looked forward to the future work. |
