Nickel-iron Based Nanocatalysts For Electrochemical Oxygen Evolution Reaction In Alkaline Media

With the rapid development of modern society,fossil fuels have been on the decline and great efforts have been made to explore sustainable and clean energy sources.Oxygen evolution reaction(OER)have always been one of the most important parts in many methods of energy conversion,especially water splitting,which suffers from sluggish reaction kinetics.Moreover,owing to low abundance and high price,noble metal based OER electrocatalysts,such as IrO2,cannot be used in wide applications though they have been regarded as state-of-art.Therefore,mountains of researches have been aiming to develop efficient non-noble transition metal based electrocatalysts.Among them,the NiFe layered double hydroxide(NiFe LDH)has been one of the most promising electrocatalysts for OER because of excellent intrinsic activity and unique structure.However,it is acknowledged that the conductivity of NiFe LDH is poor and the OER activity need further improving.In addition,it is rather simplex of those works of NiFe LDH for electrocatalytic OER,and researches on NiFe LDH-derived materials are extremely rare.To deal with above issues,this paper aims to design and synthesize efficient NiFe based electrocatalysts with special structure and outstanding OER electrocatalytic performance using facile methods.On one hand,different from traditional method,NiFe LDH microclusters with three-dimensional(3D)mesoporous hierarchical structure were prepared through a simple and economical one-step hydrothermal method with iron nitrate as Fe source,urea as precipitant and Ni foam(NF)as both Ni source and support,during which Ni2+was obtained by the reaction of Fe3+ with NF.This unique architecture could not only lead to large specific surface area and provide more accessible charge/mass transfer pathways.Moreover,the electrocatalytic performance could be further improved owing to the support NF with high conductivity and special macroporous structure.The electrochemical test results showed that only 211 mV was needed for this NiFe LDH to drive 10 mA cm-2 and rather low overpotentials to obtain higher current densities,and the Tafel slope was just 42 mV dec-1.These ultralow overpotentials and Tafel slope outline the superior OER electrocatalytic performance which is more active than most of reported electrocatalysts.On the other hand,it has been reported that transition-metal based phosphides,sulfides and selenides could perform well for OER owing to the metal-like conductivity.Therefore,facile and efficient successive two-step methods were used to synthesize ternary NiFe based derivatives(phosphide,sulfide and selenide)with NiFe LDH as the precursor.These microflowers of these derivatives were made of numerous nanosheets,and these kind of unique morphologies with 3D hierarchically porous structure could further increase the specific surface area to expose active sites and provide abundant passways to mass/charge transfer.Moreover,the special electronic structure with strong interactions between Ni,Fe and P(S or Se)could further improve conductivity and accelerate charge transfer.In addition,Ni-Fe oxohydroxide species would be formed on the surfaces of these materials during OER process as the true electrocatalytic sites.These NiFe based derivatives all can efficiently electrocatalyze OER with ultrahigh activities and superior stabilities,which ranked at the top among OER electrocatalysts.And these facile and efficient synthetic methods also were suitable for other phosphides,sulfides and selenides.