Construction Of Transition Metal Sulphide And Graphene Oxide Based Composites And Their Application In Electrocatalysis

Currently,with the rapid growth of the global population and the massive burning of fossil fuels,there is a commitment to developing clean and renewable energy sources such as solar and wind power.However,their intermittent and fluctuating power output,which is susceptible to climate and geographical location,hinders their large-scale application to modern grid systems.Commercial electrolytic water typically operates at high cell voltages with industrial current densities above 1.8 V,well above the theoretical voltage of 1.23 V,due to large overpotentials caused by hysteresis in HER and OER kinetics.The selection of efficient electrocatalysts can be effective in reducing the overpotential of HER and OER.To date,Pt-based materials and oxides of Ir or Ru are the most efficient electrocatalysts for HER and OER hydrolysis,respectively.However,the high cost and low earth abundance severely limit their widespread use.In this paper,with the objective of developing high performance hydrogen precipitation and bifunctional electrocatalysts,two different transition metal sulphide/graphene oxide composites were prepared,characterised in terms of phase and morphology,and a series of electrocatalytic performance tests by means of interface engineering and doping with non-metallic elements.In addition,theoretical DFT calculations were carried out to investigate the effect of electron redistribution on the electrocatalytic performance regarding the non-homogeneous heterogeneous interface.Details of the studies are as follows:（ⅰ）Phosphorus-doped molybdenum disulphide nanosheets（P-MoS₂/NGA）loaded on nitrogen-doped graphene oxide aerogels were designed by hydrothermal and vulcanisation methods.The three-dimensional structure of the nitrogen-doped graphene oxide aerogel（NGA）prevented the aggregation of P-MoS₂,ensuring rapid charge transfer and structural stability,while the MoS₂ nanosheets improved their interfacial properties and internal conductivity after P-doping,resulting in a highly efficient hydrogen precipitation electrocatalyst（P-MoS₂/NGA）with more surface active sites,exhibiting unexpected hydrogen precipitation reaction（HER）activity.The voltage required to achieve a current density of 10 m V cm^-1 in 1.0 M KOH is only 79 m V,while the Tafel slope is 97 m V dec^-1.Experiments and calculations show that the improved HER performance is due to doping and geometrical effects,and crucially P doping promotes optimal d band centre（εd）.The densely ordered layered structure also accelerates the electron transport in HER and enhances the catalytic activity.This effective strategy of non-metallic element doping results in unprecedented improvements in the intrinsic properties of the composites.（ⅱ）In situ conversion of NiMoO₄ to needle-like NiS₂-MoS₂ heterojunction structures on reduced graphene oxide modified nickel foam substrates（r GO/NF）by a one-step vulcanisation method.Theoretical calculations show that charge engineering modulation of electron dissipation and accumulation at the NiS₂ and MoS₂ hetero-interface optimises the reaction sites and d-band centres away from the Fermi energy level,enhancing the intrinsic catalytic activity.As expected,having a rich heterogeneous interface,abundant defects,fully exposed active sites and electronic interactions allowed the NiS₂-MoS₂/r GO/NF catalysts to exhibit excellent activity in both the oxygen precipitation reaction（OER）and the hydrogen precipitation reaction（HER）,specifically,at overpotentials of 210 and 103 m V,the OER and HER could achieve 10 m A cm^-2 current density.More importantly,when used as both cathode and anode for monolithic hydrolysis,a current density of 10 m A cm^-2 is achieved at a voltage of only 1.52 V,which is considerably better than other bifunctional electrocatalysts.It has a long-term stability of 48 h and a faraday efficiency close to100%,allowing the catalyst to be put into practical commercial applications.The present work provides a new idea for the efficient assembly of bimetallic sulphides using r GO,providing a reliable method for achieving more efficient catalytic water separation from bimetallic sulphides.