Controlled-synthesis And Electrocatalytic Properties Of Cobalt Sulfide And Composite

In recent years,energy crisis and environmental pollution have been two major problems that limit the development of human society,so it is urgent to develop new sustainable energy.Hydrogen is known as the cleanest energy in the world due to high efficiency,pollution-free and sustainability.Electrolysis water is a simple and mild way to produce hydrogen and oxygen,which has a good application prospect.It consists of two half reactions:the hydrogen evolution reaction?HER?on the cathode and the oxygen evolution reaction on the anode?OER?.However,there are some shortcomings in the process of water splitting,such as slow dynamics,large overpotential and high energy consumption.The addition of electrocatalyst can accelerate the reaction kinetics,reduce the overpotential,and greatly increase the gas release rate and yield.At present,Pt-based materials and noble metal oxides?IrO₂,RuO₂?are the best electrocatalysts for HER and OER,respectively.But the high price limits the wide use of noble metal materials.Therefore,it is of great scientific significance and practical value to study non-noble metal bifunctional catalytic materials with abundant reserves,low price,high catalytic activity and good stability for electrolytic water.Cobalt sulfide and composites have attracted much attention because of their low cost,high activity and environmental friendliness.In this paper,cobalt sulfide hollow nanospheres?Co₉S₈ HNSs,Co₃S₄ HNSs,CoS₂ HNSs?with different phases were prepared by a simple one-step hydrothermal method by controlling the reaction conditions.The formation mechanism and the catalytic performance of different phases in electrolytic water were investigated.The results showed that CoS₂ HNSs exhibited the best catalytic performance for OER and HER,which ascribed to the most the octahedrally coordinated Coⁿ⁺?n=2,3?active sites,the highest specific surface area and the S-rich nature in the pyrite crystal phase.Secondly,we synthesized the composite material of CoS₂ nanoparticles uniformly anchored on nitrogen-doped graphene?N-GP@CoS₂?by the sample one-step hydrothermal method.Nitrogen-doped graphene can provide conductive network channels and has the interaction with CoS₂ nonoparticles,thus promoting the electrochemical performance.The OER,HER and water electrolysis catalytic ability of the composites were investigated.The overpotential of OER and HER at 10 mA cm^-2 are only 243 mV and 204 mV,respectively,which also has good durabilities.The electrolysis water device was assembled by N-GP@CoS₂ as both anode and cathodewith,which has a voltage of 10 mA cm^-2 as low as 1.53 V at 60?and a faraday efficiency of nearly 100%.