Identifying The Electrocatalytic Sites Of Nickel Disulfide In Alkaline Hydrogen Evolution Reaction

Hydrogen energy is considered as the most potential energy carrier with its renewable,efficient and environmentally friendly properties.Among the various hydrogen production technologies,water electrolysis in alkaline media powered by renewable energy is the most promising approach to produce hydrogen and has been edging out the conventional methods based on fossil fuel.Transition metal disulfides（TMDs）have been extensively explored in the research field of non-noble metal electrocatalysts for hydrogen evolution reaction（HER）.Although the mechanism of TMDs catalyzing HER has been widely studied in acid solution,active sites of TMDs during the HER eletrocatalysis are still ambiguous under alkaline condition.This thesis is focusing on the synthesis and electrochemical characterization of NiS₂,detection of active sites for HER catalysis under alkaline condition by in-situ X-ray absorption spectroscopy（XAS）and the establishment of overall water splitting application.The main results are showed as follows:The chapter one introduced the background and fundamentals of electrochemical HER and different groups of HER eletrocatalysts in the field.The chapter two:NiS₂ nanosheets were synthesized on carbon cloth（CC）and nickel foam（NF）respectively by facile methods,which exhibit excellent HER performance under alkaline condition.During the HER eletrocatalysis process,an increase of HER catalytic activity was observed,indicating that an electrochemical activation of NiS₂ was involved.The chapter three:In this chapter,NiS₂ after electrochemical activation（NiS₂-A）was carefully characterized by means of characterization methods and compared with the original NiS₂.In order to eliminate the influences,electrochemical in-situ XAS was conducted directly on catalysts and the use of in-situ technology revealed that in-situ generated Ni0 from NiS₂ served as active sites for HER.The chapter four:Inspired by our findings,the in-situ generated Ni0 can be easily oxidized to Ni（OH）2 by applying anodic potentials and the obtained Ni（OH）2 can be an excellent catalyst for oxygen evolution reaction（OER）.By doping iron,NiFe hydroxide was prepared with enhanced OER activity by a similar synthesis strategy and activation procedure.The overall water splitting device was established by using NF-NiFeS₂-A and NF-NiS₂-A as OER and HER catalysts with superior water electrolysis activity and stability.