Interface Engineering And Electrocatalytic Oxygen Evolution Performance Of NiCoFe Oxyhydroxide

As an efficient,clean and abundant secondary energy source,hydrogen energy is an important part of the new energy system in the future.Hydrogen production by electrolytic water is a simple and efficient method to obtain hydrogen gas,which is widely used in hydrogen production.In the process of electrochemical water splitting,the anodic oxygen evolution reaction（OER）involves the transfer of four electrons,and its slow kinetics is an important factor limiting the efficient hydrogen production by electrolytic water.So far,relatively efficient catalysts for oxygen evolution are oxides of ruthenium or iridium,but their scarce reserves and high price hinder the industrial application of noble metal based catalysts.Transition metal-based catalyst is a good substitute for noble metal catalyst because of its abundant earth resources,low price and excellent electrocatalytic performance in alkaline environment.The deficiency of current transition metal-based catalysts is that their catalytic activity needs to be further improved.In this paper,nickel foam（NF）was used as the substrate.First,nickel sulfide crystal（Ni₃S₂/NF）was in-situ grown on the surface of NF by in-situ hydrothermal method,and then nickel cobalt iron hydroxy oxide（NiCoFeO_xH_y/NF）was in-situ fabricated on the surface of NF by electrochemical deposition.Subsequently,NiCoFeO_xH_y/Ni₃S₂/NF heterojunction catalyst was constructed using these two materials as precursors,and its electronic structure and intrinsic activity were studied in detail to clarify the mechanism of designing efficient heterojunction catalysts for electrocatalytic decomposition of water.The major study substances of this article are as follows:（1）Ni₃S₂/NF composite was prepared by one-step in-situ hydrothermal method using nickel foam and thiourea as nickel and sulfur sources,respectively.The OER catalytic activity of Ni₃S₂/NF prepared by this method was tested by electrochemical method.The results showed that the performance of Ni₃S₂/NF prepared by in-situ hydrothermal method was significantly better than that by chemical vapor deposition（C-Ni₃S₂/NF）and electrochemical deposition（E-Ni₃S₂/NF）,and the OER overpotential was 311 m V when the current density was 10 m A cm^-2.（2）NiCoFeO_xH_y/NF composite was constructed in situ by electrochemical deposition using nickel foam as support.Furthermore,XRD,SEM,XPS and other characterization methods were used to investigate the basic structure,morphology and surface electronic valence state of the catalyst.The NiCoFeO_xH_y/NF composite exhibited excellent OER properties,with an OER overpotential of 233 m V at a current density of 10 m A cm^-2.（3）Amorphous NiCoFeO_xH_y was synthesized on the surface of Ni₃S₂/NF by electrochemical deposition,and heterogeneous NiCoFeO_xH_y/Ni₃S₂/NF catalyst was formed.The results showed that the introduction of Ni₃S₂ successfully formed a heterogeneous interface between NiCoFeO_xH_y and Ni₃S₂.The coupling effect between the interface and Ni₃S₂ further reduced the voltage required for oxygen evolution reaction,thus effectively improving the OER catalytic activity of NiCoFeO_xH_y/NF.When the current density is 10 m A cm^-2,the overpotential of the catalyst is 214 m V.Secondly,the new interface formed by NiCoFeO_xH_y/Ni₃S₂/NF not only increases the active area of the catalyst,but also accelerates the transformation of OH^-to O₂under the influence of anionic element S in the heterogeneous interface,and reduces the overpotential under larger current.NiCoFeO_xH_y/Ni₃S₂/NF showed excellent OER performance,with an overpotential of 254 m V at 1M KOH and a current density of 100 m A cm^-2.