Electronic Structure Modulation Of Transition Metal-based Catalysts For Water Electrolysis

The exploration of economic,eco-friendly and sustainable energy sources for energy crisis and environmental pollution caused by the excessive consumption of transition fossil fuel admits no delay.Hydrogen（H₂）with superior utilization efficiency,pure product and high energy has achieved considerable concern in new energy field.Electrochemical water splitting is regared as a promising and attractive strategy for pure H₂ production because of its faicle reaction process and abuntant raw reactants.Unfortunately,the reaction efficiency water splitting is severely restricted by the sluggish kinetics of cathodic hydrogen evolution reaction（HER）and anodic oxygen evolution reaction（OER）.Till now,although noble Pt-and Ir O₂/Ru O₂-based materials respresent the ideal electrocatalysts for HER and OER,respectively,their exorbitant prices,scarce abundance and monofunctional activity tremendously hinder their large-scale commercialization.Therefore,it’s of vital importance to design cost-effective and high-efficiency transitional metal water splitting electrocatalysts.However,compared with noble electrocatalysts,the inferior conductivity of transitional metal（such as,Fe,Co,Ni,Mo,W,and so on）compounds results in the insufficient electrocatalytic acitivity.Plenty of researches have indicated that doping heteroatoms and constructing heterointerfaces can dramatically regulate the electronic configuration,thereby bringing about the promoted intrinsic acitivity.Hence,in this dissertation,based on the nanostructure engineering,the electronic structure of transitional-metal materials is tailored via heteroatoms incorporation and heterointerface engineering.The physical characterizatioins and electrochemical measurements techniques are employed to investigate the effect of adjustment measures on physico-chemical properties.Furthermore,the interrelationship among composition,electronic state and electrochemical performances is systematacially illustrated.Below are the research contents.1.A operable O doping strategy is employed to regulate the electronic structure of CoP nanosheets for high-performance overall water splitting.The O-doped CoP（O-CoP）nanosheets catalysts are topological converted by using as-preapredα-Co（OH）₂nanosheets as reactive precursors and structural templates through a phosphidation treatment.The O concentration in the obtained O-CoP nanosheets is facilely altered by changing phosphidation time.Experiment and density functional theory（DFT）results both confirm that the proper O incorporation could availably adjust the electron configuration of O-CoP nanosheets,and tailor the adsorption free energy of reaction intermediates on the surface of O-CoP.The optimized O-CoP nanosheets catalysts exhibit superior electrocataytic properties toward HER and OER in the alkaline solution,with the ovperpotentials of 98 and 310 m V at 10 m A cm^-2,respectively.Moreover,the two-electrode electrolyzer consisting of O-CoP catalysts as anode and cathode requires a cell voltage of 1.60 V to drive a current density of 10 m A cm^-2.2.The electronic structure of urchin-like Ni₅P₄ hollow microspheres is modulated by N incroportion,thus promoting the HER activity.The urchin-like N-doped Ni₅P₄（N-Ni₅P₄）hollow spheres are synthesized by using as-fabricated by employingα-Ni（OH）₂ hollow spheres as templates and precursors upon a Simultaneous phosphorization-nitridation reaction.This urchin-like hollow morphology could provide large contact area between electrolyte and catalyst,and benefit mass diffusion and gas release.Synergetic experimental result and DFT simulation demonstrate that the N incorporation could effectively regulate the electron density of Ni₅P₄,enlarge the exposure of active sites,and optimize the H adsorption state,thereby improving the HER performance.As a consequence,the N-Ni₅P₄ hollow spheres only need a ovepotential of 96 m V to afford a 10 m A cm^-2.3.A bifunctional CoS₂/MoS₂ nanocubes/nanosheets arrays as efficient overall water splitting electrocatlaysts are synthesized through construting interfaces.The MoS₂ nansheets（HER species）and CoS₂ nanocubes（OER species）are directly germinated on the carbon cloth（CC）to construct CoS₂/MoS₂ nanocubes/nanosheets heterostructure（CoS₂/MoS₂@CC）via a feasible hydrothermal reactioin.The numerous interfaces and nanosheets arrays endow CoS₂/MoS₂@CC catalyst superior electronic state,robust mechanical strength,abundant active centers,and multidimensional mass transfer pathways.Consequently,the CoS₂/MoS₂@CC electrode diplays excellent bifunctional electrocatalytic performances toward HER and OER in 1.0 M KOH electrolyte,with the curren density of 10 m A cm^-2 at 71 and 274 m V,respectively.Furthermore,a water splitting electrolyzer by using CoS₂/MoS₂@CC anode and cathode only need a voltage of 1.59 V to supply 10 m A cm^-2,and exhibits a faradaic efficiency of almost 100%.4.Electronic regulation by Fe incorporation and interfaces engineering to improve the OER performance of CoSe₂/Co₉S₈ heterostruture.Considering the significant modulation of electron density and electrochemical activity by heteroatom and heterointerfaces,the Fe-doped CoSe₂/Co₉S₈ heterostructure nanorods arrays on CC（denoted as Fe-（CoSe₂/Co₉S₈）@CC）is synthesized by synchronously sulfurating and selenizing the Fe-doped Co（CO₃）_0.5OH·0.11H₂O nanorods arrays grown on CC.Benefiting from the synergistic effect of Fe doping,CoSe₂/Co₉S₈ interfaces and nanorods arrays structure,the Fe-（CoSe₂/Co₉S₈）@CC sample possesses superior conductivity,adequate active sites,strong mechanical strength,and convenient charge transport channel.As a result,the Fe-（CoSe₂/Co₉S₈）@CC electrode demonstrates the current density of 10 m A cm^-2 at 243 m V,and displays the continuous operation for at least 28 h and close 100%faradaic efficiency.