The Construction Of High Efficiency Cobalt Sulfide-based Electrocatalysts And The Study Of Their Electrochemical Performance For Hydrogen Evolution Reaction

In recent years,the two major problems of energy scarcity andenvironmental pollution have gradually threatened human survival and health.It's an effective way for us to solve these two problems by obtaining green clean renewable hydrogen energy through electrcatalytic water decomposition.To date,scientists have discovered a variety of electrocatalysts?e.g.transition metal sulfides,phosphides,oxides,selenides?.Researches have shown that the electrocatalytic activity of traditional single metal sulfides still needs to be improved,While we can improve the activity following three aspects:?1?building unique nanostructures to increase the number of active sites,?2?increasing the intrinsic activity of each active site by element doping;?3?introducing conductive matrix to improve electrical contact and accelerate electron transport.In this study,hydrothermal method,stirring method,high-temperature calcination method,in-situ vapor-phase sulfurization method and vapor-phase phosphorization method were used to successfully synthesize nanocomposites,such as,Ni-Co-S,Mo,Co-NiS/NF,N,P-CoS₂@RGO,P-CoS₂@Co/C.And these materials have been appled to electrocatalytic hydrogen evolution.The specific research results are as follows:1.Constructing multi-shell hollow structure to increase the number of activesites,which can improve the performance of electrocatalytic hydrogen evolution.In this study,we mainly adjust the composition and morphology of the products by changing the sulfurization temperature and the amount of sulfur source,and further explore the relationship between their composition,morphology and their performance.The product Ni-Co-S-340?60?under the most suitabe sulfurization temperature?340°C?and the most suitable amount of sulfur?600 mg?has both complete multi-shell structure and large number of highly active components,thereby exhibiting the most efficient performance of electrocatalytic hydrogen evolution.The multi-shell hollow structure could provide a larger active area and make more active sites be exposed,which could facilitate the progress of the electrocatalytic hydrogen evolution reaction.2.Introducing the conductive base foam nickel to improve electrical contact,doping the metal elements Mo and Co to enhance the intrinsic activity,and these two aspects were combined to improve the electrocatalytic performance.In this study,we mainly investigated the effects of sulfurization temperature and the presence of nickel foam on the composition and morphology of as-synthesized products,and further explored the relationship between the composition,morphology and properties.Mo,Co-NiS/NF-400,which was synthesized with the presence of foamed nickel and under the sulfurization temperature of 400°C,has more active components,more complete morphology and more suitable active materials,thus exhibiting the most efficient performance of electrocatalytic hydrogen evolution.Nickel foam,a typical conductive metal substrate,can not only provide nickel source to form Co-Ni-S composite,but also enhance conductivity and improve electrical contact,and avoid product aggregation during the reaction.In addition,the doping of Mo and Co can optimize the electronic structure,enhance the intrinsic activity,and finally improve the electrocatalytic performance.3.Conductive carbon substrate RGO and amorphous carbon were introducedto improve electrical contact,and non-metal elements were doped to enhance intrinsic activity.N,P codoped CoS₂@RGO composites?N,P-CoS₂@RGO?and P-doped CoS₂@Co/C composites?P-CoS₂@Co/C?were synthesized by combining these two aspects,and finally applied them to electrocatalytic hydrogen evolution in all-pH solution.The experiment mainly investigated the effect of P doping towards electrocatalytic hydrogen evolution of as-synthesized products.Phosphating with short time could promote the incorporation of P into the CoS₂ lattice,which can not only increase the intrinsic activity of active site,but also limit the oxidation of the surface for sample,so that the sample maintains higher activity.In addition,the presence of RGO and amorphous carbon can effectively prevent the aggregation of active components,as well as improve conductivity and accelerate electron transport.