Preparation Of Cobalt Disulfide-based Composites And Their Electrocatalytic Performance For Hydrogen Evolution Reaction

Nowadays,the energy shortages and environmental pollution have become key issues that restrict the development of the society,which are attributed to the large-scale exploitation and overuse of fossil fuels.Therefore,the energy issues have become the main problems that need to be resolved.Hydrogen has been developed widely as new energy source due to its cleanliness and high gravimetric energy density.No greenhouse gas emission occurs in the hydrogen evolution reaction（HER）process of water electrolysis,which can produce hydrogen with high purity.Therefore,considerable attention has been paid to the hydrogen production by the water electrolysis.Electrocatalysts can effectively decrease the voltage for water electrolysis,which can reduce the energy loss.Cobalt disulfide（CoS₂）has been extensively studied due to its excellent metallic and intrinsic catalytic activity.However,the agglomeration of CoS₂can be easily found during the synthesis process,resulting in the decrease of the number of active sites.What’s more,CoS₂ also exhibits poor stability in acidic conditions.In order to further improve the HER electrocatalytic performance of CoS₂,CoS₂-based composite electrocatalysts have been synthesized in this dissertation,and the structural characterizations and electrochemical measurements have been carried out to explore their HER electrocatalytic performance.The detailed results are summarized as follows.（1）The phosphorus-doped CoS₂ composite electrocatalyst grown on the graphene（CoS₂|P/RGO）is synthesized by hydrothermal method and gas-solid reaction method.Meanwhile,the HER electrocatalytic performance of the composites have been optimized by adjusting the ratio of graphene.In acidic condition,CoS₂|P/RGO exhibits excellent HER electrocatalytic performance.The overpotential,Tafel slope and the charge transfer resistance are 132 m V,59.1 m V dec^-1 and 14.2Ω,respectively.According to the comparative experiments,the different effects of graphene and phosphorus on the improvement of the HER electrocatalytic performance of CoS₂ have been studied.The hybridization of graphene can effectively reduce the agglomeration of CoS₂ and decrease the grain size,which can expose more active sites.Due to the excellent conductivity of graphene,the charge transfer resistance of CoS₂|P/RGO is significantly reduced,which can further accelerate the electron transfer process and promote the HER process.Phosphorus doping can effectively decrease the Tafel slope and accelerate the kinetic process of the HER process.With the synergistic effects of the graphene and phosphorus,CoS₂|P/RGO exhibits excellent HER electrocatalytic performance.（2）The CoS₂/MoS₂/CFP composite electrocatalyst grown on the carbon fiber paper is synthesized by the electrodeposition method and the hydrothermal method.The optimal HER electrocatalytic performance of CoS₂/MoS₂/CFP is obtained by changing the deposition time to adjust the ratio between CoS₂ and MoS₂.In 0.5 M H₂SO₄,the overpotential,Tafel slope and the charge transfer resistance are 173 m V,102.5 m V dec^-1and 1.3Ω,respectively.In 1 M KOH solutions,the overpotential,Tafel slope and the charge transfer resistance are 133 m V,128 m V dec^-1 and 1.4Ω,respectively.The CoS₂/MoS₂/CFP composite electrocatalyst also shows excellent long-term stability both in acidic and alkaline conditions.Due to the difference in the work function of metallic CoS₂ and semiconducting MoS₂,the Ohmic contact will be formed in the contact part of CoS₂ and MoS₂,and a conductive layer will also be formed on the surface of MoS₂,which can enhance the conductivity.At the same time,new active sites are formed at the interface of the CoS₂/MoS₂/CFP heterostructure,which can further enhance the HER electrocatalytic performance of the CoS₂/MoS₂/CFP.