Preparation Of Fe, S-doped Ni-based Electrocatalysts And Their Bifunctional Electrochemical Properties

With the gradual transformation of global energy situation to clean energy,energy conversion and storage technologies have been paid more attention,such as water splitting,fuel cells,metal-air batteries and so on.Oxygen evolution reaction(OER)and oxygen reduction reaction(ORR),as the key steps of many energy conversion technologies,have slow kinetics,resulting in high over-potential and low energy conversion efficiency,which greatly hinders the development of these new energy conversion technologies.Currently,Ir O₂,Ru O₂ and Pt/C were recognized as the state-of-the-art OER/ORR catalysts,due to their superior performance.However,the scarcity and high price of precious metals increase the research cost,which is not conducive to mass production and application.Therefore,the development of non-precious metal-based OER/ORR catalysts has become a research hotspot.Among the transition metals,Fe-doped Ni hydroxide materials are widely studied because of their earth abundance and their excellent OER activity.However,the performance of catalysts is limited by the insufficient regulation of Fe element and the insufficient exposure of active sites.Therefore,it is of great significance to design a catalyst with nano-sheet structure that can adjust the ratio of Ni/Fe and has a large specific surface area to improve the Ni-based catalyst.Electronic structure of doped with sulfur adjustable catalyst to improve conductivity of catalysts,however,for the lack of S/O ratio regulation and the agglomeration of active components by high temperature vulcanization limiting the nickel-based catalysts activity,therefore,it is of great significance to develop a facile method that can regulate S/O anions to study the structure-activity relationship and maximize the exposure of active sites for further improving the S doping of nickel-based catalysts active effective strategies.The following is the main content of this article:1.The FeNiOH nanosheets with different ratios of Fe/Ni were prepared by one-step reduction with sodium borohydride at room temperature.The optimized Fe₁Ni₄OH nanosheets have larger specific surface area and a large amount of oxygen vacancy. In 0.1 M KOH electrolyte,the Fe₁Ni₄OH nanosheets have lower OER overpotential (247 m V@10 m A·cm^-2),smaller Tafel slope(87 m V·dec^-1)and better stability than Ir O₂.2.Fe₁Ni₄OH nanosheets were in situ vulcanized by anion exchange method at room temperature,and through the control of the amount of Na₂S to S/O regulation of anion with 3D nanosheet structure was successfully achieved FeNiOS-NS catalysts. The unique 3D ultra-thin FeNiOS nanosheets exhibit the excellent OER performance with an overpotential of 235 m V at 10 m A cm^-2 and a small Tafel slope of 62.7 in 0.1 M KOH,which originated from the sufficient exposure of active Fe-Ni component,high conductivity caused by S-doping,and optimized S/O ratio.3.The ORR performance of Fe₁Ni₄OH nanosheets catalysts and FeNiOS-NS catalysts were tested at 0.1 M KOH.It was found that the FeNiOS-NS catalysts showed high initial potential of 0.79 V(vs.RHE)and half-wave potential of 0.64 V(vs.RHE),which were higher than that of Fe₁Ni₄OH(the initial potential of 0.74 V(vs.RHE)and the half-wave potential of 0.57 V(vs.RHE)).The results show that S doping is an effective strategy to improve the ORR performance of catalysts.