Preparation And Water-splitting Behaviors Of Ni₃S₂-based Electrode Materials

Nickel sulfide?Ni₃S₂?possesses excellent electrical conductivity due to the metal-like band structure,so it is a kind of bifunctional water-splitting catalytic material with great potential.However,the hydrogen evolution overpotential of Ni₃S₂ is large and the hydrogen evolution kinetics is slow resulting from the high hydrogen adsorption/desorption free energy of the active sites and the small number of it respectively.And the oxygen evolution overpotential of Ni₃S₂ is large resulting from the low valence state of metal ions.In order to solve the above problems,this work took Ni₃S₂ as the researching object,Ni₃S₂-based electrode materials were prepared by plasma-enhanced vapor phosphating and iron-salt solution chemical bath treatment.The microstructure and water-splitting behaviors of electrode materials were studied systematically,and the improvement mechanism of hydrogen and oxygen evolution properties was revealed.Ni₃S₂/NF was synthesized by two-step reaction of hydrothermal method and ion exchange method.Ni₃S₂ shows the morphology of thin slices and is closely bound to the substrate.The specific surface area of thin slices is large,which is conducive to mass transfer and gas diffusion.The synthesis of Ni₃S_2-xP_x/NF was carried out by plasma-enhanced vapor phosphating of Ni₃S₂/NF.Ni₃S_2-xP_x/NF maintained the thin slices morphology,and the phosphating treatment improved the electrocatalytic performance of it.The bestperforming sample Ni₃S_2-xP_x-4 has an HER and OER overpotential of 89 mV and 216 mV respectively when the current density reaches 10 m A·cm^-2,with a lower impedance value and good stability.The synthesis of Ni₃S₂@Fe OOH/NF was carried out by iron-salt solution chemical bath treatment of Ni₃S₂/NF.Ni₃S₂@Fe OOH/NF shows a thickened lamellar morphology and a new folded structure on the laminate,and the chemical bath treatment improved the electrocatalytic performance of it.The best-performing sample NiSFe-0.01 has an HER and OER overpotential of 119 mV and 190 mV respectively when the current density reaches 10 m A·cm^-2,with a lower impedance value and good stability.Ni SFe-0.01 was used as the anode and Ni₃S_2-xP_x-4 as the cathode to assemble into an electrolytic cell,and its all water splitting performance was tested.The required total voltage of the Ni SFe-0.01|| Ni₃S_2-xP_x-4 cell is 1.54 V when the current density reaches 10 m A·cm^-2,and the cell maintains good stability.