Regulating The Catalytic Performance Of Nickel-Iron Based Electrocatalysts By Surface Adsorbed Ions

Hydrogen energy,with its advantages of high energy density and zero carbon emissions,has become an ideal energy source to replace traditional fossil fuels.Besides,using renewable electricity generated by wind and solar energy to achieve water electrolysis is also of significant interest.Water splitting includes anodic oxygen evolution(OER)and cathodic hydrogen evolution(HER).OER is the main factor limiting electrocatalytic water splitting due to its four-electron transfer process.Therefore,exploring an inexpensive,efficient,and stable electrocatalyst for OER is the key to realizing large-scale water electrolysis for hydrogen production.Moreover,replacing the less valuable but challenging OER with thermodynamically favourable and economically more attractive organic oxidation reactions is another effective way.Based on this,the research content of this paper is as follows:1.Surface-adsorbed phosphate boosts bifunctionally electrocatalytic activity of Ni0.9Fe0.1S for hydrogen production.We report a highly efficient bifunctional electrocatalyst of 3D Ni0.9Fe0.1S:Pi nano flower arrays for HER and OER enabled by surface-adsorbed phosphate.This unique nanoflower structure provides a large active surface area and the increase in electrical conductivity benefits from surface-adsorbed phosphate.Meanwhile phosphate leaching is favorable for generating more active sites.Thus,Ni0.9Fe0.1S:Pi delivers an ultralow overpotential of 175 mV to reach the current density of 10 mA cm-2.More importantly,the resulting electrode can also catalyze organic molecules such as ethanol and glycerin to be oxidized to value-added liquid products by replacing OER for hydrogen production.With the presence of glycerin,an electrolyzer assembled using the as-prepared electrode needed an ultralow potential of 1.49 V to drive a current density of 10 mA cm-2 for efficient hydrogen production.2.Surface-adsorbed sulfate boosts the catalytic performance of Ni0.9Fe0.1S/Ni3S4 heterojunction toward Oxygen Evolution Reaction.A 3D Ni0.9Fe0.1S/Ni3S4 heterojunction electrocatalyst was prepared using Ni3S4 as transition metal sulfide precursor via surface reconstruction induced by Na2SO3.It is shown that sulfate adsorbed Ni0.9Fe0.1S/Ni3S4 heterojunction exhibits superior oxygen evolution reaction activity with an exceptionally low overpotential of 152 mV at current density of 10 mA cm-2 and good stability.The extraordinarily enhanced electrocatalytic performance of Ni0.9Fe0.1S/Ni3S4 as the typical model is ascribed to not only the interfacial interaction of heterostructure,but also the systematic optimization of charge transfer,abundant electrocatalytic active sites and exceptionally effect of surface-adsorbed sulfate.This work could provide in-depth insight into designing the heterostructure coupled with surface-adsorbed acid ion on transition-metal sulfides for electrocatalytic oxidation reactions.