Transitional Metal Oxide Nanowires And Their Complex Structures Used In Efficient Energy Conversion

Cation exchange methodology in gas phase is a widely used synthesis method that can be used to control the size,shape,structure,and composition of a product.In this paper,we synthesized Zn_xCo_1-xO nanowires and NiP₂/NiO nanowires using the single-crystal ZnO nanowires as precursor by cation exchange methodology in gas phase and they were applied to the research of supercapacitor and hydrogen evolution reaction?HER?respectively.Firstly,we synthesized oxygen vacancy-rich single-crystal CoO nanowires using the single-crystal ZnO nanowires as precursor by cation exchange in gas.By controlling the exchange temperature,we can controll the ratio of Zn and Co and the single-crystal Zn_xCo_1-xO nanowires with uniformly distributed Zn and Co was obtained.By adjusting the ratio of Zn and Co,we optimized the conductivity and oxygen vacancy content of Zn_xCo_1-xO nanowires and reached the aim of accelerating the electron transport and promoting the insertion and diffusion of O^2-into materials.Zn_0.04Co_0.96O nanowire shows excellent performance when used as the positive electrode material for supercapacitor:The single-electrode capacitance reachs to806.8F/g and it has a good cycle stability.After 5000 cycles charge-discharge test,the performance can still be maintained at 89%.In addition,the NiO nanowires were also obtained by cation exchange methodology in gas phase,and then they were partially phosphatized to obtain the NiP₂/NiO composite nanowires.High-resolution electron microscopy studies show that NiO is mainly distributed in the inter area of NiP₂/NiO nanowires and NiP₂ is uniformly distributed in the outside of NiP₂/NiO nanowires in the form of particles with the diameter of about 3nm.Compared with the pure phase NiP₂,NiP₂/NiO nanowires show an excellent HER performance for alkaline HER with excellent HER activity and stability:the over-potential of 1:2 NiP₂/NiO nanowires for HER is 131mv at a current density of 10 mA cm^-2.Besides,after a long period of 20 h stability test it can still maintain the catalytic activity of 91%.We confirmed that after composited with NiO,the decomposition process of H₂O in alkaline system was promoted thereby improving basic HER catalytic kinetics.What's more,the electronic structure of NiP₂ is optimized by the electron transfer from oxygen vacancies in NiO to P in NiP₂,which adjusts the absorption/desorption effect of NiP₂ during the HER process thereby the HER catalytic activity of NiP₂ in alkaline system is improved.It is highly expected that this rational designed metal phosphide/oxide hybrid nanostructure in-situ on conductive substrate will provide new routes to practically engineer TMP-based HER electrocatalysts for industrial applications.