Sulfur Defect Regulation And Hydrogen Production By Overall Water Splitting Of Transition Metal Sulfide Electrocatalysts

With the exhausting of energy and the aggravation of environmental problems,the demand for developing renewable energy is more and more urgent.It is a promising and environmentally friendly strategy to convert electrical energy into chemical energy by electrocatalytic overall water splitting（H₂O→H₂+1/2O₂）.Overall water splitting（OWS）consists of two half-reactions,namely the two-electron hydrogen evolution reaction（HER）at the cathode and the four electron-oxygen evolution reaction（OER）at the anode.Although noble metal electrocatalyst has excellent performance,its rarity and high cost limit its large-scale application.Therefore,transition metal sulfide has become a new type of electrocatalyst with broad application prospects because of its excellent electrocatalytic activity,cheapness,easy preparation and low energy barrier in water splitting.In order to solve the problems of aggregation,low dispersion,and insufficient exposure of active sites of traditional sulfides,introducing defect engineering into sulfides is an efficient strategy.On the one hand,the doping of metal ions and the introduction of organic ligands can aggravate the sulfur defects in sulfides.On the other hand,organic ligands can also improve the dispersion of sulfides,endow metal centers with organic characteristics,improve hydrophilicity and promote electrochemical water splitting.In the first part of this study,a simple two step hydrothermal method was used to load the sulfur defect rich Mo-Ni₃S₂QDs on the nickel foam substrate.The combination ofMoion doping and the introduction of O-C=O by citric acid three sodium was used to achieve the combination of defect engineering and structural improvement.In addition,metal organic frameworks（MOFs）have become precursors and dopants for the construction of derived sulfides because of their dispersed metal centers and rich organic ligands.Therefore,in further research,MIL-88B（Ni/Mo）-NH₂ was grown on the nickel foam substrate by hydrothermal method as the precursor,and then ZIF-67 was added as a dopant to conduct vulcanization with the adding of thiourea at the same time.The bifunctional catalyst MILN-based Co（z）-NiMoS with rich sulfur defect was synthesized.The results are as followed:（1）Research on the performance of Mo-Ni₃S₂QDs.The experimental results show that high sulfur defects can be controllably prepared as the lattice mismatch and active sites can be efficiently increased via Moⁿ⁺doping.Besides,the introduction of trisodium citrate with O-C=O not only enhances the degree of sulfur defects around the metal center,changes the morphology of sulfide to distribute the active centers evenly,but also endows the metal center with strong valence changing ability.The in-situ Raman study reveals that O–C=O promotes the formation of the real active site M-OOH by the way of self-sacrifice during the OER process.The OWS system constructed by this catalyst achieved a current density of 10m A cm^-2 at a low voltage of 1.53 V and ran stably within 110 h.（2）Research on the electrocatalytic performance of MILN-based Co（z）-NiMoS.Using double MOF（the framework effect of MIL-88B and the doping effect of ZIF-67）to gradually improve the S defects.On the one hand,the unique structure of the prepared semi frame sulfide ensures hydrophilicity and high active specific surface area,which lays a superior morphological foundation.On the other hand,the coupling of metals with strong valence change ability and functional groups through active S bond plays an important role in the process of electrocatalytic reaction.Due to the activation of S bond,disintegration and reconstruction occur in the process of OER and HER.The OWS system constructed by this catalyst can obtain a current density of 10 m A cm^-2 at a battery voltage of 1.466V.the performance of the catalyst is better than Mo-Ni₃S₂ QDs and has stronger industrial application potential.