Ni（OH）₂/FeOOH@Ni₃S₂ Supported On Nickel Foam As Highly Active Electrocatalysts For Water Splitting

Water electrolysis is considered as one of the promising technologies to generate high-purity H₂ and O₂.Since metal electrodes are more tolerant in alkaline media than in acidic media,alkaline water electrolysis is more favored by scientific researchers.Currently,non-precious metal electrocatalysts have been extensively studied.Among them,Ni₃S₂ has rich Ni-S and Ni-Ni bonds,so it is theoretically considered as a bifunctional electrocatalyst with excellent performance.However,the weak OH^-capacity of Ni₃S₂ in alkaline media and the slow water molecule dissociation step limit the electrocatalytic oxygen evolution performance of Ni₃S₂.In other hand,catalyst with rich nickel-iron is used as a good OER catalyst in the water splitting field.Nickel-iron layer double hydroxides（NiFe-LDHs）catalyst such as Ni（OH）₂/FeOOH have strong adsorption ability of H₂O and OH^-which can be used as cocatalyst to accelerate the kinetics of the Volmer step-determined water dissociation during the OER for Ni₃S₂.In summary,the high-performance electrocatalysts can be achieved by synthesizing Ni₃S₂and Ni（OH）₂/FeOOH as a heterojunction catalyst.In this paper,the dual-functional electrocatalyst Ni₃S₂ and Ni（OH）₂/FeOOH was prepared by the two-step method of hydrothermal and electrodeposition.By adjusting the deposition potential,deposition time,total electrolyte concentration and electrolyte ratio that affect electrodeposition,the highly efficient dual-functional heterojunction electrocatalyst of Ni（OH）₂/FeOOH@Ni₃S₂ was optimized and synthesized.The experimental results show that the electrocatalyst Ni（OH）₂/FeOOH@Ni₃S₂ synthesized under the conditions deposition potential of-1.34 V,deposition time of 90 s,electrolyte concentration of 0.15 M and Ni/Fe ratio of 3:2 performs best electrocatalytic performance.The Ni（OH）₂/FeOOH@Ni₃S₂ only needs 240 m V of overpotential to achieve a current density of 200 m A cm^-2.In addition,its Tafel slope is only 26 m V dec^-1,indicating that its dynamic of electrocatalytic oxygen evolution process is improved.At the same time,the heterojunction catalyst also exhibits excellent electrocatalytic hydrogen evolution performance,requiring only 122 m V to achieve a current density of 10 m A cm^-2.Therefore,the catalyst is directly used as the cathode and anode for water electrolysis,and a current density of 10 m A cm^-2 can be achieved with a voltage of only 1.47 V.Moreover,Ni（OH）₂/FeOOH@Ni₃S₂able to maintained stability for 24 h stability test.Even after 5000 CV cycles at 100 m V s^-1,high OER and HER activities of Ni（OH）₂/FeOOH@Ni₃S₂ still remained.It only suffered increase 4%of OER and 7%of HER overpotential.These outstanding results demonstrate that Ni（OH）₂/FeOOH@Ni₃S₂ is a promising electrocatalyst for watersplitting.