Preparation And Hydrogen Evolution Performance Of One-dimensional Nickel-based Nanowire Arrays

Hydrogen energy has many advantages such as high combustion value and abundant sources,making it stand out among new energy sources.At present,the most valuable means of hydrogen production is through electrolysis of water technology.However,the kinetics of this reaction has slowly kinetics process,and it have to overcome the high hydrogen evolution overpotential.Because the use of hydrogen evolution catalyst can accelerate the kinetic process of hydrogen evolution reaction and effectively reduce the hydrogen evolution barrier,hydrogen evolution catalysts have been widely studied.At present,platinum-based catalysts are widely used in the commercial direction,but due to their small reserves and other defects,the large-scale application of the catalyst is limited.Therefore,the development of hydrogen evolution catalysts that are cheap,highly efficient and sufficient to replace platinum will promote the wide application of hydrogen energy to a certain extent.Because of its active chemical properties and abundant reserves,transition metal nickel has been widely studied.However,as a hydrogen evolution cathode material,metallic nickel has disadvantages such as poor stability and high overpotential,and there is still a gap for practical applications.Therefore,this article aims to improve the hydrogen evolution catalytic performance of nickel-based materials and improve their stability.In this paper,potentiostatic electrodeposition by anodized aluminum oxide template（AAO）assisted method was used to grow in situ nickel nanowire arrays with different crystal plane orientations and nickel-cobalt nanowire arrays on a titanium substrate for testing of hydrogen evolution reaction（HER）.The morphology and structure of nickel-based nanowire arrays were characterized by field emission scanning electron microscope（SEM）,X-ray diffractometer（XRD）;we used linear scanning voltammetry（LSV）,electrochemical impedance spectroscopy（EIS）and current-time curve（i-t）to study the electrocatalytic activity of nickel-based nanowire arrays for HER.By adjusting the electrodeposition parameters,nickel nanowire arrays with（220）,（200）and（111）crystal planes with preferential orientation which characterized by XRD growth were prepared.SEM results showed that the diameter of the nickel nanowires was about 100nm,and the nanowires grown in parallel and perpendicular to the titanium substrate.Using 1mol/L potassium hydroxide solution to perform LSV test on nickel nanowire arrays grown with different crystal planes,it can be seen that at a current density of 10 m A·cm^-2,the（220）crystal plane needed overpotential of 128 m V.The（200）and（111）crystal planes required 176 m V and 214 m V,respectively.At the same time,the Gibbs free energy of the hydrogen adsorption of（110）,（100）and（111）crystal planes calculated by first principles was 0.058 e V,0.180 e V and 0.215 e V.It could be seen that the（220）crystal plane of nickel had lower reaction activation energy,so it exhibited better hydrogen evolution catalytic activity,which was consistent with the experimental results.On the basis of nickel electrolyte,adding different contents of cobalt ions,by using the synergistic effect between metals to adjust the electron density of the catalyst,bimetals nanowire arrays with the ratio of nickel and cobalt of 3:1,11:1 and 32:1 were prepared.Nanowire arrays was used to promote HER performance.The LSV test results showed that when the current density was 10 m A·cm^-2,the nanowire arrays with the atomic ratio of nickel to cobalt of 32:1（NC32）needed overpotential of 103m V and it could keep the current density relatively stable within 80 h.When the atomic ratio of nickel to cobalt rised to 3:1,to achieve the same current density,the overpotential of 171 m V was required.The results of the first-principles calculation showed that when one cobalt atom was doped,that was,when the ratio of nickel to cobalt was 32:1,the Gibbs free energy of the hydrogen adsorption was the lowest(|ΔG_H*|=0.02 e V),at this time,the adsorption and desorption of hydrogen atoms tended to balance,and the HER activity of the catalyst could be improved.