Preparation And Electrocatalytic Properties Of Cobalt-based Bimetal Sulfide Oxygen Evolution Catalysts

The hydrogen production by electrolysis water technology is one of the ways to solve the current world energy crisis,and has huge development potential.However,due to the sluggish anode kinetics,the OER is inefficient and requires a high overpotential to overcome energy barriers.High over-potential will cause energy consumption and cost problems.The oxides of Ir and Ru are currently the most widely used OER catalysts,but they have obvious disadvantages such as scarcity,high price,and poor stability.Therefore,researchers are devoted to studying low-cost,high-efficiency and stable OER catalysts.Based on this,the purpose of this paper is to develop high-efficiency OER catalysts,with cobalt-based sulfides as the research object,and explore the influence of the introduction of Ni,Ag,and Cu on the performance of cobalt-based sulfides for OER catalysis.In this paper,three cobalt-based bimetallic sulfide composites were synthesized by hydrothermal and solvothermal methods.The micro-morphology and composition of the catalysts were carefully characterized by a series of methods.The OER performance and stability have also been investigated in depth.The main research is as follows:The CoS₂-NiCo₂S₄/NSG composite material was successfully synthesized by hydrothermal method,using cobalt chloride and nickel chloride as the cobalt and nickel source,respectively,and N,S co-doped graphene?NSG?as substrate.The doping of nitrogen and sulfur was beneficial to inhibit the stacking of reduced graphene oxide?rGO?.As a substrate,N,S-doped rGO improved the electron transport efficiency of the catalyst and helped to reduce the microstructure size of the CoS₂-NiCo₂S₄ active unit so that it had a larger electrochemical specific surface area and exposes more active sites.CoS₂-NiCo₂S₄/NSG showed excellent OER catalytic performance.The overpotential was only 272 mV and Tafel slope was 62.8 mV dec^-1 for current density of 10 mA cm^-2.The catalytic activity of the bimetallic sulfide was significantly better than that of any single metal sulfide under the same conditions,which could be due to the synergistic effect between Ni and Co.In addition,the 10 h i-t test also showed that the catalyst has good stability.The cobalt diethyldithiocarbamate ?Co?DDTC?₂? and silver diethyldithiocarbamate?AgDDTC?precursors were synthesized by co-precipitation method,using cobalt nitrate and silver nitrate as the cobalt and silver source,respectively.Then,by solvothermal method,using octylamine as the solvent,CoS-Ag nanowires were successfully synthesized.The study found that the superionic conductor Ag₂S mediated the formation of CoS nanowires via an atypical liquid-liquid-solid mechanism.The introduction of Ag component not only regulated the morphology of CoS,but also could improve the electrical conductivity of the material and accelerate the rate of electrochemical reaction.The CoS-Ag nanocomposite exhibited excellent OER catalytic performance.The overpotential was only 293 mV,much lower than the commercial IrO₂ catalyst?348 mV?,Tafel slope was 55.3 mV dec^-1 for current density of 10 mA cm^-2,and the mass activity was also better than reported most CoS-based catalysts.During OER operation,the sulfide catalyst undergoes phase change from sulfides to S-doped CoOOH loaded with Ag₂S specie,along with the microstructure change from nanowires to nanosheets.The sheet CuCo₂S₄ was synthesized based on the solvothermal method which using octylamine as a solvent with molecular precursors.The catalyst showed good catalytic activity.The overpotential was only 290 mV and Tafel slope was 81.3 mV dec^-1 for current density of 10 mA cm^-2.After 40 hours of catalytic stability test,the current density was only slightly reduced,indicating that the prepared CuCo₂S₄ catalyst has good electrochemical durability.During OER operation,it was found that the surface of the CuCo₂S₄ catalyst was oxidized.The real catalytically active species could be S-doped CoOOH/CuO.