Fast Preparation And Study Of Nife-Based Electrocatalysts For Oxygen Evolution Reaction

Oxygen evolution reaction（OER）is an important half-reaction in several energy conversion technologies,such as electrocatalytic water splitting,carbon dioxide reduction reaction and rechargeable metal-air battery.However,the slow kinetics of OER hinders the application of these advanced energy technologies.Therefore,the development of efficient,low-cost and stable OER electrocatalysts has currently become a research hot spot.Nickel-iron-based（NiFe-based）materials have become the most promising candidates to replace noble metal-based OER electrocatalysts due to their excellent performance and low-cost.In order to propel the commercial application of NiFe-based materials,Fe（NO）₃·9H₂O,Ni（NO）₂·6H₂O and commercial nickel foam（NF）have been used as Fe and Ni sources in co-precipitation method,ultrasonic method and Fenton-like method.Fast,simple and green methods have been developed for synthesizing NiFe-based compounds,which are also applied to electrocatalytic OER.The details are shown as follows:1.A heterostructured NiFe-LDH/CeO₂ with a tight interface between ultra-small ceria nanoparticles and a monolayer nickel-iron bimetallic layered hydroxide material has been prepared by one-step coprecipitation of Ni²⁺,Fe³⁺,and Ce⁴⁺ions in a solution containing formamide.The characterization and experimental results show the strong electron acceptor Ce⁴⁺with high work function can extract electrons from the Ni site,promoting the oxidation of Ni²⁺to Ni³⁺and significantly reduce the redox energy barrier of Ni²⁺/Ni³⁺in the NiFe-LDH/CeO₂ heterostructure.As a result,the NiFe-LDH/CeO₂exhibits excellent OER performance with a low overpotential of 216 mV at the current density of 10 mA cm^-2 and low Tafel slope of 74.1 mV dec^-1 due to the accelerated electron transfer from the strong interfacial interaction between CeO₂ and monolayer NiFe-LDH.This work provides a new perspective for the rapid co-precipitation of NiFe-LDH-based OER electrocatalysts.2.An amorphous nickel-iron-cobalt ternary hydroxides（NiFeCo-OH）on NF has been rapidly in-situ synthesized of by utilizing the cavitation effect of the solution in the ultrasonic environment.The extremely transient environment generated by the ultrasonic cavitation effect endows NiFeCo-OH a highly active amorphous structure as well as excellent physical and chemical stability.Meanwhile,the synergistic effect induced by Co doping promotes the oxidation of Ni sites and exposes more active sites.In the three-electrode electrolysis cell,NiFeCo-OH exhibits excellent OER activity(overpotential of 236 mV at 100 mA cm^-2)and stability(reaction over 100 h at a current density of 100 mA cm^-2).This new strategy opens up a new route for in situ synthesis of highly active NiFe-based hydroxides for practical applications.3.The iron oxyhydroxide and nickel-iron bimetallic layered hydroxide heterostructures（FeOOH/NiFe-LDH）has been prepared by one-step Fenton-like reaction.On the solid interface of FeOOH and NiFe-LDH,the strong electronic interaction between FeOOH with high crystallinity and NiFe-LDH with low crystallinity can promote the electro-oxidation of active Ni sites and enhance the intrinsic OER activity of NiFe-LDH phase.In addition,the special heterostructure extends the solid-solid interface,which further strengthens the electronic interaction.The entire reaction process costs only 1 minute.Thus,the FeOOH/NiFe-LDH showed excellent OER activity and stability,with an overpotential of 238 mV at 100 mA cm^-2and a Tafel slope of 28.9 mV dec^-1.What’s more,the reaction was stable under 1.6 V for more than 700 h.This work provides a fast,simple and green new strategy for designing NiFe-LDH-based materials for OER.