| Energy shortages and environmental pollution are two crucial challenges facing humanity today.As a result,major concerns have been raised over the development of new energy sources.To date solar energy is a kind of renewable energy with huge potential.Hydrogen has become one of the most promising energy sources by virtue of its high energy density,clean and renewable advantages.However,the problem of conversion and storage hinders the development and utilization of solar energy.Hence,solar energy is converted into hydrogen by electrolyzing water,which is a fantastic strategy to solve energy and environmental problems.The water splitting reaction consists of hydrogen and oxygen evolution half-reactions.Generally,the oxygen evolution reaction(OER)involves four proton-electron transfers to oxide water to oxygen.Thus,the sluggish kinetics causes OER is a bottleneck for the development of total hydrolysis.At present,for OER catalysis,IrO2 and RuO2 are reasonable active catalyst.However,owing to their scarcity and high cost,their commercial application become difficult.Therefore,the design and development of high efficiency OER catalysts have become the priority in the evolution of electrocatalysis.Furthermore,the intrinsic activity of catalysts is usually determined by the electronic structure,so it is of great significance to research the electronic structure of catalysts to guide the design of high-efficiency catalysts.In this paper,high purity samples of NiS2,NiS and Ni3S2 were prepared to study the correlation between their electronic structure and OER performance,following research results were obtained:(1)The OER performance of Fe doped NiS2Herein,NiS2 is a semiconductor with a band gap of 0.3 eV With the doping of Fe,the state density near its Fermi level was increased,result in a transformation to metal state gradually and the improvement of conductivity,correlated with increasing OER kinetics.In the work presented here,Fe0.1Ni0.9S2 has the best OER activity,exhibiting low overpotential(270 mV at 10 mA cm-2)in 1M Fe-free aq.KOH.Meanwhile,exploring the real active sites of metal sulfide for the OER remains a frontier in research.According to X-ray diffraction(XRD),Scanning electron microscope(SEM)and Transmission electron microscope(TEM)characterization of different samples after OER,we found that the sample was partially crystallized with the proceeding of OER.Further,TEM and X-ray photoemission spectroscopy(XPS)was used to analysis morphology,the result indicates the amorphous species may be Ni-Fe hydroxyl oxide,which properly is the real active species of Fe0.1Ni0.9S2 during process of OER.(2)A novel method for preparing high purity Ni,Sy(NiS2 NiS and Ni3S2)with different stoichiometric ratioAccording to the phase diagram of NixSy,NiS(?-NiS and ?-NiS)NiS2 Ni3S2 Ni3S4,Ni7S6 Ni6Ss and Ni9Ss are included.The multiplicity of phases makes the synthesis of a single pure phase of nickel sulfide very difficult in this field.In this paper,high purity of single samples(NiS2 NiS and Ni3S2)were prepared synthetically by introducing reductive agent into the synthetic system creatively and adjusting the reaction time.This method is applicable to the pure phase synthesis of binary heterogeneous sulfides such as CoxSy and FexSy,significantly.(3)The electronic structure of NiS2,NiS and Ni3S2The intrinsic properties of a substance were determined by their electronic structure.Based on the advantages of synthetic high-purity NixSy(NiS2 NiS and Ni3S2),we used advanced techniques such as synchrotron radiation photoelectron spectroscopy(XPS)and synchrotron radiation absorption spectroscopy(XAS)to discuss the electronic structure of NiS2 NiS and Ni3S2.It is not difficult to find that from NiS2 to NiS to Ni3S2,as the proportion of sulfur decreasing,nickel sulfide gradually changes from semiconductor to metal.Research and understanding of electronic structures are good guideline for the design of highly effective catalyst materials. |
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