Study On Ni-Co-Fe Based Electrocatalysts And Their Performance In Oxygen Evolution Reaction

With the development of industry,the consumption of fossil fuel is increasing gradually.The excessive utilization of fossil fuels has brought two major issues:energy crisis and environmental pollution.Hydrogen energy with zero carbon emission and high energy density has been recognized as a promising alternative of traditional fossil fuel.Electrocatalytic water splitting is one of the most promising and efficient strategies for sustainable hydrogen production.The overall water splitting reaction consists of an anodic oxygen evolution reaction（OER）and a cathodic hydrogen evolution reaction（HER）.Due to high overpotential and sluggish kinetics,oxygen evolution reaction（OER）at the anode side is usually considered as the limiting rate reaction for electrocatalytic water splitting.Ir/Ru-based materials are considered as the state-of-the-art catalysts for OER.However,high cost and scarcity severely impede their large-scale application.Exploring highly efficient non-precious metal oxygen evolution reaction electrocatalysts is imperative.This paper focus on the preparation of self-supported electrocatalysts,OER activity and the mechanism for OER activity enhancement.The main contents of the paper are as follows:（1）W-doped Ni Fe layered double hydroxides（denoted as Ni Fe W LDH）on nickel foam（NF）were synthesized via a facile hydrothermal method.The shift of peaks in XRD and XPS results results confirm that the high-valence states W species were successfully doped into Ni Fe LDH.The scanning electron microscopy（SEM）and transmission electron microscopy（TEM）images of Ni Fe W LDH shows the open porous structure with interconnected nanosheets growing vertically on NF substrate.Ni Fe W LDH presents superb OER activity with a low overpotential of 295 m V at 50 m A cm^-2,accompanied by excellent stability in 1 M KOH electrolyte.The Raman and XPS characterizations reveal that mixed-valence-state tungsten dopant could act as a strong Lewis acid to strengthen the oxidation effect of Ni²⁺to Ni³⁺during OER process.Theoretical and experimental studies reveal that the doped W into Ni Fe LDH can tailor the electronic configuration and decrease the adsorption energy barrier,thereby boosting the OER catalytic activity.This work clarifies the mechanism for OER activity enhancement of Ni Fe LDH after introducing tungsten.（2）We in-situ fabricated bimetallic Ni C₂O₄-Co electrocatalyst on nickel foam（NF）by a facile one-step solvothermal method in this work.The nanostructures are tightly grown on the3D foam substrates,which provides a strong integrative interaction between the active phases and substrate and good conductivity.Nanorods and nanoplates of Ni C₂O₄-Co1 are mixed and grown together.Due to the existence of the gap between nanorods and nanoplates,Ni C₂O₄-Co1owns high specific surface area,which facilitated access of electrolytes and ensuring fast release of gas bubbles.With an optimized molar ratio,Ni C₂O₄-Co1 self-supported electrocatalyst presents superb OER performance with a low overpotential of 278 m V at 10 m A cm^-2 and a Tafel slope of 65 m V dec^-1,accompanied by excellent stability in 1 M KOH electrolyte.The superior catalytic activity of bimetallic Ni C₂O₄-Co electrocatalyst is attributed to optimized electronic structure,rapid interfacial charge transfer and the synergistic effect between Ni sites and Co sites during OER process.This work paves a new and facile path to explore the design of transition metal oxalate as electrocatalysts for oxygen evolution reaction.