Preparation And Electrochemical Oxygen Evolution Reaction Performance Of Nickel Based Chalcogenides And Phosphorous

Electrochemical oxygen evolution reaction(OER)gets much attention in the last fewdecades because of its prime role in water splitting,rechargeable metal-air batteries and fuel cells.However,the kinetics ofOER is very sluggish because the evolution of an oxygen molecule typically requires multi-steps reactions with four-electron transfer,which leads to a large overpotential for electrochemicalOER.Therefore,stable and efficient electrocatalysts are essential forOER to achieve low overpotentials and practical reaction rates.Over the past few years,noble-metal-based oxides have been recognized as the benchmark electrocatalysts for water oxidation due to the outstanding activity and stability in acidic solution,unfortunately,the high prices and scarcity severely limit their widespread application asOER catalysts in energy devices.In recent years,transition metal Nickel-based materials have drawn great attentions forOER electrocatalysis owing to the similar electronic structures to noble metals such as Ru,Ir and Pt.Recent advances have demonstrated that Nickel-based sulfides,phosphides and selenides can become promising alternatives for these noble-metal-based oxides due to their low cost and intrinsic activity.However,the surface reconstruction on catalyst materials due to the in-situ electrochemical oxidation tuning ofOER will lead to the formation of new active materials,thus affecting the activity ofOER electrocatalysis.In this work,Nickel-based chalcogenides and phosphides are prepared via mechanical alloying and hydrothermal reaction to investigate the electrochemicalOER performances.More importantly,the surface reconstruction on catalyst materials via the in-situ electrochemical oxidation is used to further enhance electrochemicalOER performances.Firstly,nanocrystalline NiS powders are prepared by mechanical alloying with Nickel andSulfur powders as reactants.As a novel electrocatalyst,the electrochemicalOER performances of nanocrystalline NiS are investigated and the effects of surface reconstruction derived materials forOER electrocatalysis are discussed.Secondly,heterostructures of Co Ni₂S₄/Ni₃S₂ on nickel foam(Co Ni₂S₄/Ni₃S₂@NF)are synthesized by the one-step hydrothermal method as promising electrocatalyst forOER.Furthermore,the effects of in-situ electrochemical tuning on Co Ni₂S₄/Ni₃S₂ heterostructures forOER electrocatalysis are discussed.We report heteroatoms Fe alloying into NiS₂ crystal via mechanical alloying method to prepare nanocrystalline(Fe_xNi_1-x)S₂ powders as pre-catalysts toward electrochemicalOER.With the in-situ electrochemical oxidation tuning,the electrochemicalOER performances of(Fe_xNi_1-x)S₂/CFP electrodes obviously improved.Further investigations reveal that the derived hybrids of Fe₃O₄ nanoflakes and nanoporous Ni doped FeOOH are true active materials for the(Fe_0.5Ni_0.5)S₂ underOER conditions.This study not only reveals the true active materials of the heteroatom alloyed bimetallic sulfides,but also provides a facile strategy to regulate the formation of active materials for enhanced oxygen evolution catalysis.NiSe nanorods based on nickel foam(NiSe@NF)are synthesized by hydrothermal reaction as pre-catalysts toward electrochemicalOER.A shell of NiO nanosheets is in-situ formed on the NiSe nanorods'surface after the in-situ electrochemical oxidation tuning on NiSe@NF electrode,forming the so-called NiSe-NiO core-shell structure(NiO/NiSe@NF).Furthermore,we find that theOER performances of NiO/NiSe@NF electrode can be further improved via electrochemical deposition of heteroatoms Fe into NiO nanosheets.Therefore,the modification of in-situ electrochemical oxidation tuning derived active materials in a promising method to enhanceOER performances.To get insight into the roles of non-metallic elements from the corresponding non-oxide materials,nanocrystalline Ni₅P₄ is prepared by mechanical alloying method as the pre-catalyst forOER.We find that NiO nanosheets with abundant crystal defects are formed on the surfaces of Ni₅P₄ particles during the electrochemical process.The effects of the in-situ P incorporation in surface reconstruction derived NiO forOER electrocatalysis are discussed.Theoretical calculations reveal that the heteroatom P doping into NiO crystal can weaken the binding strength of theOER intermediates,change the potential-determining step and achieve a lower theoretical overpotential.The present work provides a novel mechanism of the enhanced electrocatalytic performances of non-oxides materials forOER electrocatalysis by highlighting the effects of surface reconstruction induced in-situ heteroatoms doping in derived active materials.