Studies On Electrodeposition Of Co And Co-Ni Alloys From Ionic Liquid And Their Catalytic Performance For Hydrogen Evolution Reaction

Co and Co-Ni alloys materials can be used as a replacement for noble metal Pt electrode on hydrogen evolution reaction（HER）because of their low cost,excellent cycling stability and electrocatalytic properties.Therefore,the technology and mechanism of the electrodepositions of Co and Co-Ni alloys from a mixture system of 1-ethyl-3-methylimidazole bisulfate（[EMIM]HSO₄）and ethylene glycol（EG）are studied,and the electrocatalytic properties for HER in alkaline medium of Co and Co-Ni alloy obtained from this system are evaluated.Firstly,the electrodeposition and electrocrystallization mechanisms of Co²⁺in[EMIM]HSO₄-EG system are studied using cyclic voltammetry（CV）and chronoamperometry（CA）technique.The CV results reveal that the electrochemical reduction of Co²⁺to Co occurs through a one-step two electrons transfer and the process is irreversible and diffusion-controlled.The diffusion coefficient of Co²⁺in[EMIM]HSO₄-EG system is calculated to be 2.24×10^-6 cm~2·s^-1（T=323K）.The CA tests showed that the mechanism of nucleation/growth for Co on GC electrode in this system is dependent on the deposition voltage.At low overpotentials,they are most likely involves the 3D progressive nucleation mode and changes to 3D instantaneous at higth overpotentials.The effects of deposition potential,current density and temperature on the Co deposit thickness also are investigated.SEM result shows that the Co coating presents a fibrous surface morphology with many bundles of elongated crystals randomly distributed throughout the coating.EDS analysis shows that the Co coating obtained from this system with contents of Co（96.51%）,C（1.88%）and O（1.61%）.XRD test shows that the coatings are crystalline and the Co grains are fine with an average size about 11 nm.The overpotenital value for HER in 1 M KOH solution of Co catalyst prepared under optimal conditions from this system,when the catalytic current density reaching 10 m A·cm^-2,is 199 m V.Then,the electrochemical behavior of Co-Ni codeposition in[EMIM]HSO₄-EG system and the catalytic performance for HER of Co-Ni coatings obtained form this system are investigated.The results reveal that the codeposition of Co-Ni is anomalous and the mechanism of nucleation/growth for Co-Ni on GC electrode involves to 3D instantaneous mode.SEM result shows that the Co-Ni coating presents a uniform surface morphology with many“rambutan-like”grains.EDS analysis shows that the Co-Ni coating obtained from this system with contents of Co（36.51%）,Ni（60.74%）,C（1.79%）and O（0.96%）.XRD test shows that the coatings are crystalline and the Co-Ni grains are fine with an average size about 14.6 nm.The overpotenital value for HER in 1M KOH solution of Co-Ni catalyst prepared under optimal conditions from this system,when the catalytic current density reaching 10 mA·cm^-2,is 139 mV.