Synthesis And Electric Catalytic Properties Of Nickel-Cobalt Bimetallic Compounds

With the deepening of industrialization,the problems of excessive energy consumption and aggravation of environmental pollution have become increasingly prominent.Therefore,the exploration of safe,clean,and highly efficient renewable energy sources has become one of the research hotspots.As water is a renewable,non-polluting and clean energy source,all countries in the world will develop water energy as a priority for energy development strategy.There are four major reactions related to water in electrocatalysis,including hydrogen evolution reaction(HER),oxygen evolution reaction(OER),oxygen reduction reaction(ORR)and hydrogen oxidation reaction(HOR),in which hydrogen evolution reaction and oxygen evolution reaction are two half reactions of water decomposition reaction.The oxygen evolution reaction involves four electron transfer reactions and is a slow kinetic reaction.Its overpotential is much higher than the hydrogen evolution reaction and it is the main factor that limits the efficiency of water decomposition reactions.Therefore,the research focus of the oxygen evolution reactions is to accelerate the reaction kinetics of high-efficiency catalysts.For the time being,OER's catalytic performance is optimized for noble metal anodic oxygen evolution materials such as Ru and Ir.OER activity of these precious metal materials is good and relatively stable,but due to its limited storage and high price,it can not achieve large-scale production.Therefore,we must find cheaper metals to replace precious metal materials as OER catalysts.Compared with other transition metal monoatomics or compounds,nickel-cobalt compounds have excellent OER catalytic activity,good stability and low cost.Therefore,they have received extensive attention from researchers and have become the hotspot of current research.Studies have shown that by increasing the active sites exposed of nickel-cobalt compounds and their electrochemically active surface area or doping with non-metal anions or increasing electron transport capabilities can effectively increase catalyst activity.In this paper,to improve the catalytic activity of the catalyst,the electrochemical deposition method was used to directly grow nickel-cobalt compounds on a three-dimensional porous nickel foam substrate as an electrocatalyst to accelerate water decomposition reactions,and we systematically explored the influence of the structure,composition,and shape of the catalyst on electrochemical properties of water decomposition reactions,which provides an important idea for the synthesis of similar nickel-cobalt-based OER catalysts.The main research contents of this article are as follows:The first chapter of this thesis is an introduction,summarizing the research progress of electrolytic oxygen evolution reactions,the application status of electrochemical deposition method in electrochemical materials,the classification of OER catalysts,and the advantages of nickel-cobalt bimetallic compounds as OER catalysts.The research direction and experimental program of this article is described.The second chapter of this article is to choose the three-dimensional network foam nickel as the conductive substrate,distilled water as the solvent,surfactant as the topography regulator,cobalt nitrate and nickel nitrate as the precursor,the use of DC power through electrochemical deposition method,prepared a 3D hierarchically nickel-cobalt layered double hydroxide(Ni-Co LDH)catalyst with a regular mesoporous nanosheet structure.Different pore sizes of Ni-Co LDH nanosheet catalysts were obtained by adjusting precursor species,charge ratio,electrochemical deposition time,and surfactant type.By the characterization methods include XRD,SEM,TEM,EDX,BET,FITR,and XPS,the phase state,structure,size,morphology,specific surface and pore structure,groups,surface element composition and valence of the material of the Ni-Co LDH nanosheet catalyst were scientifically analyzed.The characterization results show that the Ni-Co LDH catalyst have a great electrochemical properties dependence on its structure,size,conductivity and surface properties.Among them,the addition of the surfactant cetyltrimethylammonium bromide has greatly improved the oxygen evolution reaction's performance of the synthesized Ni-Co LDH catalyst,and the current density can be achieved 100mA/cm~2 at an overpotential of 292 mV.At the same time,it has a great stability.This material provides a new idea for improving electrochemical performance.In chapter 3,based on the study of Ni-Co LDH catalysts,the effects of different anions on the electrochemical performance of the catalysts are further discussed.We used electrochemical deposition methods to prepare a series of Ni-Co-Se with three-dimensional hierarchical structures and Ni-Co-S nanosheets by adjusting the feed ratio of Ni and Co precursors.Studies on the relationship between the composition and electrochemical properties of nickel-cobalt oxygen compounds are very valuable in water decomposition reaction.Through XRD,SEM,TEM and XPS characterization methods,the phase state,structure,size,morphology,surface element composition and valence of the material were analyzed scientifically.At the same time,the electrocatalytic performance of Ni-Co-Se and Ni-Co-S catalysts was systematically studied by using electrochemical test methods such as LSV,EIS and CV.The results show that it has excellent electrocatalytic activity and stability.In chapter 4,based on the studies of Ni-Co-Se and Ni-Co-S catalysts,the effects of P ions on the electrochemical performance of the catalysts are further explored.A series of Ni-Co-Se-S and Ni-Co-Se-S-P materials were prepared on the NF by electrochemical deposition method,and high activity was found by adjusting the ratio of Se and S and whether they were annealed.For the water decomposition reaction,the studies on the relationship of composition-property of nickel-cobalt compounds are very valuable.By XRD,SEM,TEM and XPS and other characterization methods,the phase state,structure,size,morphology,composition and valence of surface elements were scientifically analyzed.At the same time,the electrocatalytic performance of Ni-Co-Se-S and Ni-Co-Se-S-P catalysts was systematically studied by electrochemical testing methods such as LSV,EIS and CV.The results show that it has good electrocatalytic activity.The fifth chapter of this article summarizes the work done during my master's degree,and at the same time makes a reasonable prospect for future research.