Ion Regulation Of Transition Metal Nickel- And Cobalt-base Compounds For Electrocatalytic Perfomance

With the increasing demand and consumption of fossil fuels,the development of energy conversion and storage technologies is imminent.Electricity-driven water splitting as an effective energy conversion technology has been attracted great attention.The water-splitting reaction can be divided into two half reaction:the hydrogen evolution reaction(HER)and the oxygen evolution reaction(OER).However,the efficiency of the total system is inhibited by the sluggish kinetics of the electrode reactions,resulting in excessive overpotential.Although some noble metal-based catalysts have shown efficient eleccatalytic performance,high cost and low abundance have hindered their commercial application.Therefore,there is an urgent need to develop transition metal-based electrocatalysts that are inexpensive,efficient and stable.Among them,nickel and cobalt,which are abundant elements on the earth,have been extensively applied in the electrocatalytic materials.These Ni-and Co-based electrocatalysts include oxides,phosphides,sulfides,layered double hydroxides and metal-organic frameworks,which are expected to replace precious metal-based materials as a new generation of electrocatalysts.This paper has carried out a train of works on Ni-and Co-based materials,aiming at preparing highly active electrocatalysts by ion regulation and exploring the catalytic mechanism.The specific research content of this paper is as follows:(1)Using Co3O4 as the precursor,we demonstrated a facile method to confine abundant oxygen vacancies into Co3O4 nanoparticles via a simple hydrogen gas treatment.Introducing abundant oxygen vacancies in Co3O4 quantum dots will increase the proportion of Co2+/Co3+increases.Since the tetrahedral Co2+ site in the Co3O4 framework tends to form cobalt oxyhydroxide(CoOOH)species,which provides more active sites.In addition,the electronic conductivity test confirmed that the electron transfer capability becomes better as the content of oxygen vacancies increases.The active site and electronic structure are optimized simultaneously based on defect engineering,so that the oxygen-defect-abundant Co3O4 exhibits good OER electrocatalytic activity and stability under alkaline conditions.(2)We confined fluorine anion(F)into three-dimensional nickel foam by a one-step calcination method,thereby constructing a simple platform for studying the influence of F anion on improving OER catalytic activity.The strongly electronegative F anion is favorable to build weak metal-fluorine bonds,which is easy to surface reconstruction for forming active species of nickel oxides/hydroxides during the OER process,and consequently the electrocatalytic performance is enhanced.Compared with bare nickel foam,F-modified nickel foam has better OER catalytic activity and stability in alkaline medium.Moreover,this method can be extend to other Ni-based catalysts(F-NiAl LDH-NF)for higher catalytic activity,thereby proving the universality of the method.(3)The synthesis of Ir-doped Ni(OH)2 nanosheet in-situ grew on the nickel foam(NF)substrate via a one-step hydrothermal method.The introduction of Ir effectively regulated the formation of nanosheet morphology,successfully improving surface area and exposing more active sites,which significantly realizes the HER and OER catalytic performance with high activity and durability.Moreover,Ir-Ni(OH)2@NF was served as the cathode and anode respectively to drive water splitting in basic environments,achieving a current density of 10 mA·cm-2 at a low potential of 1.54 V.