In Situ Electrochemical Activation Construction Of Transition-Metal-Based Electrocatalysts And Catalytic Performance For Water Electrolysis

Water electrolysis is a promising and clean technology for hydrogen energy in the future.It utilizes abundant and cheap water as raw material and intermittent electrical energy input from renewable energy.However,water electrolysis is a typical heterogeneous reaction,of which the hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）efficiencies are essentially dependent on the catalytic interface activity and microstructure.Currently,the inexpensive transition metal（Fe,Co,Ni and Mo,et al.）based elecrocatalysts are the most widely researched.Their catalytic properties are mainly improved by three roles-the nanostructure design,the conductivity enhancement and the regulation of electronic structure of catalytic sites.However,the systematic and efficient study on the catalytic interfaces are seldom researched.In fact,it is crucial and challengable to the regulate and optimize the microstructure,composition and active sites on the catalytic interface.In this paper,electrochemical in-situ activation technology is adopted to regulate the catalytic interfaces.On basis of the desigining nanostructure and enhancing the conductivity,the specific electrochemical process is exerted on the surface of electrocatalyst.The electrochemical oxidation or reduction reaction（generation of oxide film or chemical valence changes）takes place in the electrolyte,which modifies and optimizes the structure,composition and the active sites on catalytic interface.The changing rules on the structure,composition and valence state on catalyst surfaces are systematically studied as well as the effects on catalytic properties.The structure-activity relationship is also revealed.The specific research results are as follows:By means of one-step hydrothermal synthesis of Ni foam-supported Ni₃S₂ nanowire electrocatalyst,the microwave（household）-assisted oxidation was utilized to efficiently accelerate the electrochemical activation（cathode activation）and constructed a highly active NiO_x/Ni₃S₂ heterogeneous catalytic interface.The NiO_x and Ni₃S₂acclerated the first（rate-detemining step）and second reaction step in alkaline HER process.The synergistic catalysis was realized on heterogeneous catalytic interface and the alkaline HER performance Ni₃S₂ nanowire was improved.By means of one-step hydrothermal synthesis of Ni foam-supported vanadium sulfide/nicke sulfide hybrid nanorod electrocatalyst,the vanadium element was proved to efficiently accelerate the electrochemical activation on nickel sulfide.The vanadium oxyhydroxide was in situ generated on surface of nickel sulfide to enlarge the site density,while the nickel oxyhydroxide was formed to improve the stability.Furthermore,by means of two-step hydrothermal and gaseous sulfurization synthesis for amorphorous vanadium-doped nickel sulfide nanoclusters supported on Ni foam,the bimetallic nickel-vanadium oxide-sulfide was in situ formed as double catalutic site by electrochemical activation and realized efficient synergistic HER process.It was proved that the slight changes of vanadium was able to precisely tune the electronic structure and catalytic activity of Ni site in nickel sulfide.In addition,the doping of niobium（Nb）and tantalum（Ta）with similar electronic structure with vanadium were also proved to accelerate the electrochemical activation of nickel sulfide.The vanadium was capable of accelerating other nickel-based materials（such as nickel selenide,phosphide and oxide）and improve the activity,revealing the intrinsic fact that electrochemical activation modified the metal sites.By means of hydrothermal and gaseous phosphidation processes for Ti foil-supported cobalt,nickel and iron-based phosphide nanowire electrocatalyst,the cathodic activation was utilized to improve the HER performance.The electrochemical activation was realized either by modifying the electronic structure of active sites or by in situ generation of oxide-phosphide hybrid catalytic interface.It was confirmed that it was crucial to modify the electronic structure of metal site to improve the catalytic performance.The electrochemical corrosion-deposition method was adopted,where the nickel foam was utilized as working electrode to provide the Ni source and the iron foil was utilized as the counter electrode to provide the Fe source.The Ni-Fe oxide film catalyst was synthesized by cycling voltammetry on the surface of Ni foam,which realized the direct construction of a highly active catalytic interface is achieved by electrochemical etching-deposition method.The effects from tuning the structure and composition of oxide film and the catalytic activity was systematically studied,and the structure-activity relationship was revealed.In summary,the electrochemical pretreatment or synthesis process provide useful reference for designing active nanostructured electrocatalysts.They also provide new idea to study the catalysis mechanism on catalytic interface and the structure-activity relationship.The electrochemical activation technology has advantages such as simple operation,mild conditions,precise control,strong flexibility and environmental friendliness.It is expected to be applied to many other energy conversion and storage field with heterogeneous reactions.