Interfacial Modification Of Nickel-based Sulfides And Study On Dynamic Process In Oxygen Evolution Reaction

The continuous consumption of non-renewable kerosene,oil and natural gas and other energy sources leads to global warming,environmental damage and other problems.Extensive attention has been paid to exploring clean and renewable novel energy sources.It is an important way to obtain clean hydrogen energy by electrolysis of water.The oxygen evolution reaction is the rate-limiting step due to its high energy barrier.Therefore,developing high activity,economic friendly,non-toxic,safe and reliable electrochemical materials has become one of the most urgent research topics worldwide.Nickel-based-oxides and nickel-based-sulfides have been utilized extensively on OER due to their unique electronic structure,abundant reserves and various lattice structures.Transition metal sulfides are inclined to reconstruct the surface and have excellent catalytic activity.On the other hand,transition metal oxides have advantages in catalytic stability.In this study,we explored the reconstruction process and speculate the real active site is sulfur atom doping NiOOH.In addition,we provided an insightful understanding of the poor stability of NiS.To improve the stability,we construct the cladding-type NiO/NiS.To balance the activity and stability,we obtained the different thickness of NiO layer by changing calcination temperature.In situ characterization would be preferred to investigate the function of interface and the improvement of stability.Finally,three interface materials,NiS₂/NiO,NiS/NiO,and Ni₃S₂/NiO were synthetized.Combined with in situ characterization and spectroscopic analysis,it was proved that the three interfacial materials have improved the stability of nickel sulfides.Furthermore,the different substrate effects caused by the different structures of the three nickel sulfides were elucidated.This paper provides a new idea for the reconstruction mechanism of oxygen-sulfur compounds and the rational design of oxygen-sulfur interfacial compounds.NiS was synthesized by electrodeposition and tubular furnace deposition.To suggest the unfavorable electrochemical stability,multifarious operando characterizations and electrochemical measurements were monitored to investigate the reconstruction process.Specifically,the sulfides reconstruct into layeredγ-NiOOH that is the real catalytic sites by means of chemical electroxidation.At the same time,the unfavorable soluble Ni³⁺is obtained,which is undesirable for catalytic stablility.Cladding-type NiO/NiS were synthesized by the modified method.Furthermore,we obtained the different thickness of NiO layer by changing calcination temperature.To date,most studies have proved the reconstruction layer of oxides is less than 4 nm.To balance the activity and stability,the NiO/NiS with 6 nm NiO layer was choosed as research object.The atoms in the interface are arranged in S-Ni-O.In addition,according to XPS and XRD,NiOOH/NiO/NiS was obtained after reconstruction.The NiO layer can protect NiS from drastic reconstruction,and the NiS layer can doping a small amount of sulfur atoms in the NiOOH layer due to the difference between the solution and NiS layer.The reconstructed material has a fair stability（>500 h）.The reason for the improvement of its stability is that the interfacial material is conducive to oxygen evolution based on the adsorption oxygen mechanism and inhibits the oxygen evolution based on the lattice oxygen mechanism.Moreover,the NiO coating can make the reconstruction more reversible and inhibit the nickel ion precipitation.Three kinds of interfacial material NiO/NiS,NiO/NiS₂,NiO/Ni₃S₂ were synthesized by changing the calcination temperature and the mass of sulfur powder.Combined with in situ characterizations and spectroscopic analysis,it was proved that the stability of three interfacial were improved.Furthermore,the different substrate effects caused by the different structures of the three nickel sulfides were elucidated.