Preparation Of Nickel And Nickel Oxide Powder Using Plasma Discharge Electrolysis

Plasma discharge electrolysis is easy to operate,simple in equipment and no need to control atmosphere.And this process is widely used in surface modification,wastewater treatment and nanomaterials preparation.Recently,nickel and nickel oxide powder has a wide application prospect in terms of energy battery and 3D printing material.However,the current preparation process of nickel and nickel oxide powder are restricted by equipment and cost.Therefore,technological innovation for preparation Ni/NiO is urgent.In this study,a new preparation process,plasma discharge electrolysis,was used to make nickel and nickel oxide powder.Preparation of nickel oxide powder using plasma discharge electrolysis in nickel sulfate electrolyte was conducted.The content of nickel oxide powder obtained by plasma discharge electrolysis increased firstly and then decreased with increasing of nickel sulfate concentrations in the solution,and the content of NiO reduced gradually with the increase of the applied electrolytic voltage and the electrolysis time.When the experiment was perform in 0.4 mol/L nickel sulfate solution at 150 V for 20 minutes,the purity of obtained nickel oxide powder is 98.96%.Plasma discharge electrolysis using multi-electrode showed that the nickel oxide powder can be obtained by reasonably controlling the discharge time.When the eight-cathode plasma discharge electrolysis is adopted,the yield conforms with the equation:m=1.81t+0.65.The reaction mechanism of producing NiO by plasma discharge electrolysis is divided into four steps.Firstly,ionization of gaseous molecules between cathode and solution,which result in formation of plasma,and it contains strong reductive species like hydrated electrons and hydrogen radicals by H2O+e-(?)eaq-,H·,OH·,H2,H2O2,H3O+.Secondly,the reduction reactions take place.The metal cations Ni2+ become Ni atoms involve the ea-and H· radical according to following reactions:eaq-(H·)+Ni2+→Ni+,eaq-(H·)+Ni+→Ni0.Thirdly,Ni atoms undergo the nucleation process,nano-sized materials are generated by crystal growth and coalescence in the bulk solution.Finally,the high temperature in glow discharge area results in the oxidation of highly active nickel to nickel oxide by reaction of Ni+H2O→NiO+H2(g).Nickel powder can be prepared by plasma discharge electrolysis in a low-chloride nickel sulfate solution,and the particle size of nickel powder is related to both the concentration of nickel ion and electrolysis time.Decreasing of nickel ion concentration and shortening of electrolysis time are beneficial to obtain smaller particle size of nickel powder.The median diameter of nickel powder obtained by inert anode electrolysis is smaller by 2.55 μm than that with soluble nickel as anode.The yield of nickel powder is 4.4 times than that of single cathode when five cathodes are employed,the purity of nickel powder is 98.63%.The first three steps of producing nickel by plasma discharge electrolysis is the same as that of generating NiO process.However,the process of preparing nickel powder using plasma electrolysis belongs to partial plasma electrolysis and there is no glow emitting in the discharge area,and the temperature of the reaction zone is low,which lead to nickel particles cool directly by the bulk solution without oxidation.