Rational Design Of Cobalt/Nickel/Selenium-Doped Iron Sulfide Nanoplates For Electrochemical Water Splitting

Electrochemical water splitting is a promising technology to produce hydrogen,which is a renewable,secure,and environmentally friendly source of energy.Electrochemical water splitting provides a viable path to produce hydrogen including two half reactions with the hydrogen evolution reaction（HER）on the cathode and oxygen evolution reaction（OER）on the anode.The overall efficiency,however,is strictly constrained by the sluggish kinetics of the four-electron transfer process for the OER.The development of efficient,low-cost catalyst electrodes for water splitting reactions is necessary to make this process cost effective.In this paper,the cobalt-doped and nickel-doped pyrrhotite-type Fe S nanomaterials and sulfur-doped Fe Se₂ nanorod bundles were synthesized by a one-step hydrothermal method.These three materials exhibited good HER and OER performance in alkaline electrolyte.Firstly,we design and develop novel Co-doped Fe_0.95S_1.05 nanoplates,which were synthesized using Fe（CO）₅ as precursor for the first time via a one pot reaction.Fe_0.9Co_0.05S_1.05 lead to enhanced OER activity with a low overpotential of 252 m V at 10m A/cm²,small Tafel slope of 46 m V/dec,as well as improved HER activity with a Tafel slope of 114 m V/dec and a density of 10 m A/cm²at an overpotential of 342 m V.Co²⁺ions play important roles in promoting the OER activity,due to more valence 3d electron orbits.Thus,we inferred that the d orbitals of Fe and Co is responsible for the good electrochemical OER performance.Secondly,a series of nickel-doped pyrrhotite iron sulfide(Fe_0.95-xNi_xS_1.05)nanosheets were successfully synthesized via a facile and scalable one-step hydrothermal in p-xylene.We then developed the as-prepared Fe_0.95-xNi_xS_1.05 nanosheets as highly active and robustly stable electrocatalysts for OER and HER in alkaline media.For OER,Fe_0.8Ni_0.15S_1.05 exhibited superior electrocatalytic performance which afforded a current density of 10 m A/cm² at overpotential 228 m V and a Tafel slope of 53 m V/dec.The HER activity was achieved on Fe_0.8Ni_0.15S_1.05 with a Tafel slope of 103 m V/dec and a current density of 10 m A/cm² at an overpotential of 263 m V.The synergistic effect of Fe and Ni elements can affect the surface morphology to expose more active sites and improve the charge transfer between the doped metal and the host metal atoms.Finally,we present a new type of Fe（Se_xS1-x）₂ nanorod bundles,which were successfully synthesized via a simple one-step hydrothermal method.We further demonstrate the applicability of these structures as electrocatalysts for OER application.More interestingly,the as-prepared Fe(Se_0.5S_0.5)₂catalyst exhibits the best OER performance with an overpotential at 10 m A/cm²of 247 m V,a low Tafel slope of 54m V/dec,and excellent catalytic stability.The incorporation of S causes lattice strain and lattice defects to provide more active sites,and optimizes the electronic structure,thereby improving the performance of the electrocatalyst.These results presented here may provide new opportunities for discovering effective and low-cost electrocatalyst materials for water electrolysis.