Supercritical Ethanol Deposition And Electrochemical Properties Study Of Carbon Cloth-nickel Hydroxide/nickel Doped Cobalt Phosphide Composites

Carbon-transition metal hydroxide/phosphide nanocomposites have the characteristics of low cost and high electrochemical activity,and have been extensively studied in the field of electrochemical energy storage and conversion.In this work,a supercritical ethanol deposition method is adopted to prepare carbon cloth-nickel hydroxide and carbon cloth-nickel doped cobalt phosphide nanocomposites with a self-supporting structure,and such composites are studied as solid flexible supercapacitor electrodes and electrocatalytic water splitting electrodes,respectively.Due to the gas-like diffusivity and near-zero surface tension characteristics of the supercritical ethanol fluid,the nano-arrays with a hierarchical porous structure are uniformly deposited on the porous activated carbon cloth.The unique self-supporting microstructure exposes more active sites and provides effective ion transport channels.Accounting the high conductivity of carbon cloth,good electrochemical performance is obtained.The main research contents of this thesis are shown as follows:1.Electrochemical Activated Carbon Cloth?ECC?is obtained by activating the commercial carbon cloth in a strong acid electrolyte.The surface of the ECC existence abundant pores and functional groups after the activation process.ECC can not only be used as an ideal substrate for depositing active materials but also exhibit high electrochemical performance when it is directly used as the negative electrode of a supercapacitor.2.Ni?OH?₂ nanosheets?NSs?are grown on the ECC substrate with a self-supporting microstructure by using an efficient supercritical ethanol deposition method.By adjusting the amount of the reactants,the microstructure can be optimized.The prepared Ni?OH?₂ NSs/ECC flexible electrode shows a specific capacity of 918 mC cm^-2 at a current density of 2 mA cm^-2,and has good rate capability(68.4%specific capacity retention at a current density of 20 mA cm^-2).Flexible solid supercapacitor assembled with Ni?OH?₂ NSs/ECC as the positive electrode,ECC as the negative electrode,and polyvinyl alcohol-KOH as the solid electrolyte has a working window of 1.8 V and an energy density of 8.3 mWh cm^-3 at a power density of 20 mW cm^-3.3.Ni-doped CoP?Ni-CoP?nanoarrays are grown on the ECC substrate by using the supercritical ethanol deposition method followed by a phosphating process.By optimizing the composition of the active material,the synergistic effect between Ni and Co can be promoted.The Ni-CoP/ECC composite electrode exhibits high hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?bifunctional catalytic activity.At a current density of 10 mA cm^-2,the HER overpotential is 110 mV,and the OER overpotential is 330 mV.A voltage of 1.66 V is required when the current density reached 10 mA cm^-2 for the overall water splitting electrolyser constructed with Ni-CoP/ECC bifunctional catalyst.