Synthesis Of Self-supporting Transition Metal Nanocomposites For Electrocatalytic Hydrogen Production

Electrocatalytic water splitting has been regarded as a secure and efficient approach to generate clean hydrogen energy.At present,platinum-based catalysts are generally considered to be the most effective electrocatalysts,but Pt is expensive and scarce,limiting the commercial applications of catalysts.Therefore,the development of high-efficiency and low-cost non-precious metal catalysts has become important.Most of the common electrocatalytic materials are powders,which need to be fixed on the glassy carbon electrode with organic adhesives（such as Nafion and PVDF）.However,the binder will reduce the conductivity of the material,and will cover some active sites of the catalyst to reduce the catalytic activity.In situ synthesis three-dimensional self-supporting electrode without binder has larger active specific surface area and more active catalytic sites,it is beneficial to transport of electron and proton,and exhibiting excellent catalytic performance.However,the sluggish anodic oxygen evolution reaction（OER）imposes a considerable overpotential requirement in electrocatalytic water splitting.Therefore,we consider the solution from two aspects:Firstly,the urea oxidation reaction（UOR）is a highly efficient method.It only needs0.37 V vs RHE voltage to reach the equilibrium potential,which is much lower than that of the oxygen evolution reaction（1.23 V vs RHE）.Urea-assisted electrolysis of water,combined with HER and UOR,can significantly reduce energy consumption.Secondly,the interaction between the reactant and the catalyst surface is affected through the introduction of photothermal effect to improve the catalytic effect.In this work,three-dimensional self-supporting electrodes were prepared with nickel nanorod arrays and nickel foam as the substrate,their ability of electrocatalytic water splitting and urea oxidation assisted H₂ production under photothermal conditions were studied,respectively.The main research contents are as follows:Firstly,Ni Co₂O₄ nanorods grown on the nickel nanorod arrays substrate were prepared by a hydrothermal reaction,and then added sodium hypophosphite by phosphatization to grow Ni₂P shells under N₂ atmosphere.Finally,a hierarchical Ni Co₂O₄@Ni₂P nanorods grown on nickel nanorod arrays（Ni Co₂O₄@Ni₂P/NAs）was obtained.The catalyst has large active specific surface area and good HER and OER performance.As a bifunctional catalyst,it only required 1.58 V to achieve current density of 10 m A cm^-2,which is superior to most reported catalysts.It shows that the self-supporting transition metal phosphide catalyst promote the catalytic reactions effectively by providing lots of channels for electron transfer and exposing more active sites.Secondly,Ni-Ni O grown on nickel foam（Ni-Ni O/NF）was synthesized by hydrothermal and reduction reaction.The catalyst has excellent performance of UOR and HER in alkaline solution.The performance of urea oxidation further improved under light irradiation.Photothermal effect improved electrocatalytic activity by increasing density of electronic states and accelerating the reaction kinetics.And as a bifunctional catalyst,the overpotential is only required 1.49 V,which is 0.05 V lower than that without light irradiation.It shows that the photothermal effect effectively promotes the catalytic activity and stability of urea electrooxidation.