Preparation Of Multimetal Based (oxy)hydroxides And Research On Electrocatalytic Anodic Reaction Of Water Electrolysis

Towards water electrolysis,the anodic oxidation reaction involving multiple electron transfer leads to sluggish kinetic process,resulting in high energy consumption,which hinders the practical application of sustainable water electrolysis technology for hydrogen production.The development of new low-cost,efficient electrocatalysts are expected to break this dilemma.Nickel-based materials generally have structural and compositional characteristics suitable for catalytic anode reactions,can derive highly active hydroxyl oxides under oxidation conditions,therefore have received extensive research attention.Design and construction of nickel based catalysts,as well as research on their modification,with the intention of improving their catalytic performance,face enormous challenges.This paper adopts the doping strategy and electrochemical synthesis method to prepare three nickel-based multi-metal co-doped（oxy）hydroxide catalysts with remarkable performance,labled as NiCoFeO_xH_y,NiCoFe-OOH NTs and NiCoMoCu-OOH NDs,respectively.By improving the electrocatalytic anode reaction performance to realize low-energy water electrolysis for hydrogen generation,and constructing experimental and theoretical analyses,the relationship between the structure-composition and the catalytic performance was studied.NiCoFeO_xH_y catalysts were prepared via a one-step electrodeposition strategy,in which nickel-cobalt-iron ternary nitrate-based bath was employed as electrolyte,and nickel foam performed as the substrate.The catalyst exhibits excellent alkaline OER activity with an overpotential of 194 m V at a current density of 10 m A cm^-2.In-depth research and analysis show that compared to single metal（Coor Fe）doping,bimetallic co doping optimizes the electronic structure of nickel hydroxide to reduce the rate control step energy barrier of OER.In addition,bimetallic co doping caused the catalyst to occur during the OER processβ-NiOOH directionγ-NiOOH phase transition behavior of NiOOH.These positive effects together improve the overall dynamic process of OER,while can operate stably for 50 hours.Based on the excellent intrinsic activity of nickel-cobalt-iron-based（oxy）hydroxide,it is feasible to optimize the nanostructure of the catalyst to further improve the OER performance.NiCoFeNTs pre-catalysts with hollow nanotube array structure was synthesized by a Zn O template-assisted electrodeposition strategy using nickel foam as a substrate.NiCoFe-OOH NTs can in-situ derive a highly active ternary（oxy）hydroxide layer on the surface during the OER processes.The alkaline electrocatalytic performance of NiCoFe-OOH NTs was tested,with an overpotentials of 187 and 310 mV at current densities of 10 and 500 mA cm^-2,respectively,along with 50 h long-term stability.Subsquently,the modulation mechanism of catalyst morphology,composition and structure on the activity was studied;the unique hollow array feature increases the active area of the reaction,and at the same time effectively regulates the catalyst-solution interface state,which significantly accelerates the electrochemical reaction mass transfer rates.The NiCoMoCu-OOH NDs catalyst with dendritic morphology was fabricated on the surface of nickel foam via a bubble-template electrodeposition and followed by an electrochemical activation.By virtue of the high intrinsic activity of nickel-based（oxy）hydroxide in the electrocatalytic proton-coupled electron transfer（PCET）reaction,and the multi-metal co-doping effect actively modulates the coordination environment and charge distribution of the reactive site,NiCoMoCu-OOH NDs delivers the working current densities of 10 and 500 m A cm^-2 under 1.32and 1.52 V vs.RHE towards UOR,which is significantly lower than the OER.Further studies revealed the derived（oxy）hydroxide performed as the real active species.OH^-distribution in the catalyst-solution interface layer also has a direct effect on the kinetic rate of UOR process,that is,high OH^-concentration can promotes the（oxy）hydroxide active layer reconstruction and facilitates the deprotonation reaction of urea molecules.Meanwhile,it is eluviated that the tip effect generated by the high-curvature nanostructure features of NiCoMoCu-OOH NDs induce local OH^-enrichment on the surface,thus ensuring the considerable UOR performance at high operating current densities.NiCoMoCu-OOH NDs acts as bifunctional catalyst of the electrolyzer shows excellent performance for urea-assisted water electrolysis.It only requires 1.50 V to reach 100 m A cm^-2 with stable operation,and continuously and operate for 48 hours in a flowing electrolytic cell.Through electrochemical synthesis methods,controllable preparation of three highly active hydroxyl oxide catalysts was achieved.The results of in-depth mechanism research show that the electronic structure of the catalyst can be flexibly adjusted by doping modification strategy,thus improving its intrinsic activity;At the same time,the influence mechanism of the morphology characteristics of the catalyst on the kinetic properties and catalytic activity in OER and UOR was elucidated.The research content in this article can provide reference for the research and development of anode catalysts for electrolytic water in the futures.