Deep Eutectic Solvent Assisted Strategy For Synthesis Nickle Sulfide/Graphene For Electrocatalysis Performance

The rapid consumption of fossil fuels has caused serious energy shortage and environmental problems which forced us to have a further research on green renewable energy conversion and storage technologies.Among a variety of candidates,hydrogen,due to its high gravimetric energy density and no harmful products after combustion,has long been considered as the most promising energy carrier.Electrochemical water splitting for sustainable hydrogen production from renewable sources?e.g.,sunlight and wind? is a prospective and appealing approach to address the aforementioned global energy-related issues.In this thesis,deep eutectic solvent?DES? was synthesized by hydrogen bond donor?NiCl₂·6H₂O? and hydrogen bond acceptor?alcohols,carboxylic acids,amides? at a certain temperature,and nickel sulfide hybrid graphene was prepared by a simple one-step pyrolysis and sulfidation process.Nickel sulfide/graphene composites with nanosheet/core-shell structure were prepared by regulating the composition,molar ratio,pyrolysis temperature and pyrolysis time of DES.DSC,FTIR,NMR,XRD,XPS,Raman,BET,ICP-OES,EA,SEM,TEM,STEM,EDS-mapping,AFM,and other characterization methods were employed to analyze the phase composition,structure and morphology of the composite materials.The electrocatalyzed water splitting reaction was carried out on the prepared materials by an electrochemical workstation.The main research contents are as follows:?1?First,the 2D/2D NiS/graphene nanosheet composites were prepared by one-step pyrolysis and sulfidation of DES formed by NiCl₂·6H₂O and polyethylene glycol 200?PEG 200?.The prepared 2D/2D NiS/graphene nanosheet composites showed excellent hydrogen evolution reaction?HER? and oxygen evolution reaction?OER? activity in alkaline solution,and overpotential of HER and OER at 10 mA·cm^-2 current density is only 70 and 300 mV,respectively.The current density of 10 mA·cm^-2 can be achieved at 1.54 V voltage when it is used as the cathode and anode material for the overall water splitting.?2?Secondly,NiS₂@G composite materials with core-shell structure were prepared by forming DES with NiCl₂·6H₂O and malonic acid as precursors.The prepared core-shell structure material can effectively inhibit the corrosion of the core layer material,and synergistic effect can be formed between different components to improve the material properties.The prepared material exhibited excellent electrocatalytic performance for HER and OER in a 1.0 M KOH electrolyte.The synthesized NiS₂@G composite material can be used as bifunctional catalyst for overall water splitting to obtain the current density of 10 mA·cm^-2 at 1.52 V.?3?Finally,nitrogen?N?doped graphene composite NiS₂ materials?N-G/NiS₂? were prepared by forming DES with NiCl₂·6H₂O and urea as precursors.Due to the high conductivity of N-G and the synergistic effect between N-G and NiS₂,the water splitting reaction can be effectively promoted.The composition,pyrolysis temperature and pyrolysis time of DES were optimized.At a current density of 10 mA·cm^-2,the HER overpotential was 78 mV and the OER overpotential was 264 mV.N-G/NiS₂ exhibit excellent electrocatalytic performance when it was used as the anode and cathode catalyst for the overall water splitting.?4?In addition,this method can be extended to NiCl₂·6H₂O and other organic alcohols and carboxylic acids to form DES for the preparation of nickel sulfide hybrid graphene materials.Moreover,it can be further extended to the preparation of metal sulfide?such as iron sulfide,cobalt sulfide,copper sulfide? composite graphene materials.It provides a new synthetic route for the preparation of metal sulfide/graphene composites.