Phase Engineering And Heteroatom Doping Of NiSe₂ Nanostructures For Enhanced Electrocatalytic Water Splitting

Hydrogen energy,due to its high energy density and zero carbon emissions,has become a new energy source with high hopes for mankind.Electrochemical water splitting is considered as one of the most effective routes to convert electrical energy into chemical energy stored by hydrogen fuels.However,the conversion efficiency is limited by the inherent slow reaction kinetics,especially the four-proton coupled electron transfer pathway of OER.Therefore,the exploration of active electrocatalysts that can lower the kinetic barriers of OER has become a leading topic in the field of hydrogen energy research.At present,although some precious metal-based electrocatalysts?such as Ru O₂ and Ir O₂?have outstanding catalytic performance,their limited reserves and high cost have prevented their large-scale commercial use.Therefore,it is urgent to explore advanced catalysts featuring low cost,high abundance and high electrocatalytic activity.Faced with these problems,this paper carried out the preparation of iron-doped pyrite nickel diselenide(m-Ni_1-xFe_xSe₂)and its electrocatalytic OER performance.In this work,a simple colloidal synthesis route has been developed to prepare the m-NiSe₂ and the m-Ni_1-xFe_xSe₂ with various Fe dopant contents?x=0.03,0.06,0.12?.Different ratios of NiCl₂·6H₂O and FeCl₃·6H₂O were used to tune the Fe dopant content in the resulting products.In addition,through an annealing treatment,the transformation of nickel diselenide from the marcasite phase to the pyrite phase(p-Ni_1-xFe_xSe₂)was successfully achieved without changing the morphology of sample.With the component and structural characterization by Raman spectroscopy,X-ray diffraction,X-ray photoelectron spectroscopy,field emission scanning electron microscopy and field emission transmission electron microscopy at al,the succeed synthesis of Ni_1-xFe_xSe₂and its crystal phase transition were proved,and the appearance of all the samples are similar to nanodendrites.Atomic ratios of the samples were carried on atomic absorption spectrometry analysis.In this work,synergistic modulations of metallic NiSe₂ nanodendrites by phase engineering and heteroatom doping are achieved to promote OER.On the one hand,phase engineering to synthesize marcasite NiSe₂nanodendrites offers a better intrinsic electronic conductivity than the pyrite phase.On the other hand,heteroatom Fe doping in marcasite NiSe₂ nanodendrites further gains electronic benefits and meanwhile provides more electrochemical active sites owing to heteroatom displacement defects.Consequently,an optimized catalyst of m-Ni_0.94Fe_0.06Se₂ nanodendrites with a moderate dopant content is developed,exhibiting significantly improved OER performance with a low overpotential of 279 mV at 10 m A cm^-2,a small Tafel slope of 39 mV dec^-1 and long operation stability of 35 h in 1.0 M KOH,which is even better than that of the precious metal-based catalyst Ir O₂.According to the Raman,XPS and TEM characterization of the catalyst after the OER stability test,in-situ surface oxidation of the m-Ni_0.94Fe_0.06Se₂ nanodendrites to form amorphous Fe-doped Ni OOH/Ni?OH?₂ shells during OER process is demonstrated,which contributes to the superior activity and outstanding stability.This work provides valuable insights into the design of advanced OER electrocatalysts by means of combinational modulations of phase engineering and heteroatom incorporation.