Transition-metal Sulphides And Phosphides Composite:Preparation And Their Application For Electrochemical Water Splitting

Hydrogen（H₂）is an attractive alternative to fossilfuels because of its high energy（120 MJ/Kg）,clean and renewable nature.Electrochemical water splitting is the widest method to get H₂ and it is constituted by the hydrogen evolution reaction（HER）and the oxygen evolution reaction（OER）.Platinum and its compounds are the most effective electrocatalysts for HER,ruthenium and iridium compounds are the most effective electrocatalysts for OER by now,however their scarcities greatly and high cost limit their large-scale application.As a result,designing effective and low cost electrocatalysts to decrease the overpotential and energy in water splitting process has attracted much attwntion.The main work is as follows:（1）Porous NiCo₂S₄ network have been successfully synthesized by a facile one-pot solvothermal method without the use of any surfactant or template.Crystal structure,morphology,composition and surface area of the as-synthesized samples were characterized by X-ray diffraction（XRD）,field-emission scanning electron microscopy（SEM）,X-rayphotoelectronspectroscopy（XPS）and Brunauer–Emmet–Teller techniques（BET）.Owing to its porous nature and small crystalline size,the NiCo₂S₄ network showed good HER performance in 1M KOH solution,the Tafel plots of NiCo₂S₄ network is 117.7 mV/dec,the overpotential is 250mV at the current density of 10 mA/cm².And the current density almost has no change after 1000 cycle CV measure.NiCo₂S₄ network also have a high specific capacitance of 1250 F/g at 1 A/g,and excellent cycling stability with the retention capacity of 70.3%after 5000 cycles in the 3M KOH solution.（2）Sheet-shaped Co₂P-CC（CC:carbon cloth）is successfully synthesized by a facile route.The electrochemical measurements demonstrate that sheet-shaped Co₂P-CC exhibits an exceptional HER activity with an overpotential of 94 mV at the current density of 10 mA/cm² and a small Tafel slope of 80 mV/dec in 1M KOH solution.Similarly,sheet-shaped Co₂P-CC also has good HER performance in 0.5M H₂SO₄ and 0.5M phosphate buffer solution（PBS）,whose overpotential is 95 and 231mV at the current density of 10 mA/cm²,respectively.Sheet-shaped Co₂P has a large surface area which can provide more active sites,and CC is an excellent conductive substrate which can enhance the conductivity of the electrocatalyst.These outstanding results show that sheet-shaped Co₂P-CC can be an excellent candidate for highly efficient electrocatalysts.（3）In this work,nanosheet-shaped CuS was successfully grown on CC using a two-step method in combination with electrodeposition and hydrothermal treatment via in-situ sulfidation of Cu₂O and Cu with exposure to thiourea solution at 120oC for 24 h.XRD,XPS,SEM,and transmission electron microscopy（TEM）were employed to characterize the composition and the morphology of the as-synthesized nanosheet-shaped-CuS-CC samples.The electrochemical measurements demonstrate that the synthesized nanosheet-shaped-CuS-CC electrocatalysts possess superior OER activity and outstanding long-term durability in 1M KOH electrolyte.In particular,the nanosheet-shaped-CuS-CC synthesized via electrodeposition process at the applied current of 1.5 mA/cm² shows a low overpotential of 358 mV for OER at the current density of 10 mA/cm².The excellent OER activity can beattributed to the synergistic effects between nanosheet-shaped CuS and conductive CC.Hence,the nanosheet-shaped-CuS-CC is a promising material for oxygen evolution reaction.