Fabrication Of Transition Metal Based Nanosheet Array Electrodes And Their Catalytic Performance Toward Photo-Electrochemical Oxygen Evolution Reaction

The large-scale application of hydrogen energy has gradually become the trend of energy structure development,and the cheap and efficient hydrogen production is the basis for achieving this trend.Electrocatalytic or photoelectrocatalytic water splitting to generate hydrogen is an appealing way due to its environmental and mild characteristics.Water electrolysis consists of two half reaction named oxygen evolution(anode reaction)and hydeogen evolution reaction(cathode reaction).In the water splitting process,the anode reaction of oxygen evolution reaction(OER)is the rate-determining step.This is because the sluggish OER step involves a complex four-electron transfer process.Thus,the efficient OER electrocatalyst is required to promote the reaction rate.So far,IrO2 and RuO2 are known to be the benchmark OER electrocatalysts.However,the high cost and scarce nature undoubtedly hinder their applications at large scale.Considering the catalytic activity and production cost,transition metal based OER catalysts have attracted more and more attention.Although much progress has been made,their catalytic performances are still far from satisfactory because of the intrinsic low electrical conductivity,insufficient active sites and immoderate water adsorption ability.Starting with the electronic or crystal structure,we prepared highly efficient transition metal based OER catalysts.For the problem of insufficient active sites,we explored two methods to prepare catalysts with nanosheet array structure.The fabricated catalysts with nanosheet array structure may possess larger surface area expose more electroactive sites.Furthermore,we report a designed synthesis of a novel OER electrocatalyst of porous CoON PNS-400 nanosheet array by the nitridation of Co(OH)2 nanosheet array under 400 ? for efficient electrochemical water oxidation.Benefiting from the porous nanosheet architecture,enhanced electric conductivity and moderate free energy for adsorbed intermediates,the novel CoON PNS-400 exhibited superior electrocatalytic activity for OER with a low overpotential of 0.23 V to achieve the catalytic current density of 10 mA cm-2 and a small Tafel slopes of 48 mV dec-1.In addition,we fabricate ternary amorphous CoFe-H nanosheet array by the introduction of Fe atoms into Co(OH)2 nanosheet array.Benefiting from the synergistic effect Fe between and Co,as well as the amorphous nature of CoFe-H,the CoFe-H nanosheet array exhibit superior OER catalytic activity in alkaline environment with a small overpotential(0.28 V)to achieve significant oxygen evolution(j = 10 mAcm-2)and a low Tafel slope(28 mV dec-1).We utilized the same facile electrodeposition method to directly deposit ultrathin amorphous CoFe-H nanosheet(3-7 nm)on a BiVO4 photoanode by simply decreasing deposition time,constructing a novel integrated CoFe-H/BiVO4 photoanode.The CoFe-H/BiVO4 photoanode exhibited a significantly enhanced photocurrent density of 2.48 mA cm-2(at 1.23 V vs reversible hydrogen electrode(RHE))and a much lower onset potential of 0.23 V(vs RHE)for PEC-OER.Careful electrochemical and optical studies revealed the importance of improved OER kinetics,high-quality electrocatalyst/semiconductor interface,and excellent optical transparency to achieve such high PEC performance.In this thesis,we aimed at designing and developing highlg efficient transition metal based OER catalysts.We investigated the relationship between electronic(and/or crystal structure)and OER performance.We also constructed novel integrated catalyst/semiconductor photoanode with high-quality interface and conformal core-shell structure,leading to an enchanced photoelectrocatalytic oxygen evolution performance.This work provides a possibility for rationally designing ternary transition metal compounds as advanced OER electrocatalysts and also provides general guidelines for designing efficient PEC systems.