Nucleation Mechanism And Growth Process Of Nickel In Nickel Sulfide Soluble Anode/Sulphate System

With the development of modern industry,the application of nickel began to shift from traditional industries to high and new technology fields such as electroplating and high-temperature alloys.For a long time,nickel electrocrystallization,as an important stage of nickel electrodeposition process,has been a research hotspot.Most scholars at home and abroad choose glassy carbon electrode as the matrix,and use traditional watt type electrolytes to study the electrocrystallization process of nickel.Although many research results have been achieved,the guiding significance for actual industrial production is extremely limited.At present,the electrolytic nickel produced by nickel sulfide electrorefining accounts for more than 90%of the total nickel production in China,while the industrial electrolyte of nickel sulfide soluble anode/sulphate system,due to its complex metal ion composition,makes the requirements for the matrix of nickel electrocrystallization process more stringent than the traditional watt electrolyte,and also makes the original complex electrocrystallization process more complex.The different substrates have a great influence on the electrocrystallization process of nanocrystalline nickel in an industrial electrolyte with complex compositions.The effects of three different substrate materials?glassy carbon,gold,and nickel electrodes?on the electrocrystallization behavior of nanocrystalline nickel in an industrial electrolyte with complex compositions were studied by cyclic voltammetry?CV?,single potential step chronoamperometry,SEM and AFM.The CV results indicated that the initial deposition potentials of nickel shift to the positive direction in the order glassy carbon<gold<nickel electrodes,while the nickel deposition overpotential decreased at the same time.Chronoamperometry results indicated that from the glassy carbon to gold and nickel electrodes,the adhesion of nickel nanoparticles on the electrodes increased,nucleation relaxation time became shorter,and the number of nuclei decreased.The electrocrystallization process on the surfaces of glassy carbon,gold,and nickel electrodes changes from a three-dimensional continuous nucleation/growth mechanism to a three-dimensional instantaneous nucleation/growth mechanism,but the time of the transition is differ ent.For longer deposition time,the size of the nickel nanocrystals changed from non-uniform to uniform,which is consistent with the growth law from continuous nucleation to transient nucleation.As the deposition potential is negatively shifted and the deposition time is prolonged,the I-t curve for the nickel and gold electrodes is more stable and reliable than those from the glassy carbon electrode.At the same time,the integrity and uniformity of the nanocrystalline nickel deposited on the nickel and gold electrodes are superior to those on the glassy carbon electrode.So,gold and nickel electrodes are more suitable for prolonged high-potential electrodeposition experiments in complex electrolyte systems than glassy carbon electrodes.It is worth noting that the electrocrystallization process of nickel is complicated by the complex ionic components in the industrial electrolyte of the nickel sulfide soluble anode/sulfuric acid system.Electrochemical quartz crystal microbalance?EQCM?and cyclic voltammetry?CV?were used to study the cathodic deposition and anodic dissolution process of nickel on gold electrodes in industrial electrolytes and the effect of temperature on this process.The results show that the M/n values of the I and II deposition zones were 30.8 and 29.3 g/mol,respectively,and the M/n values of the III-1 and III-2dissolution zones were 30.7 and 29.4 g/mol,respectively,showing that the cathodic deposition and anodic dissolution of Ni correspond to the two-electron processes.At the same time,at 25,30 and 35?,the M/n values of the deposition peaks were 30.3,30.9 and 26.3 g/mol,respectively.The metal ions(Co²⁺,Cu²⁺)which are similar to the nickel deposition potential will co-deposit with Ni²⁺,and the kind of metal ions co-deposited with Ni²⁺tends to be complicated with increasing temperature.Properly raising the temperature is beneficial to the deposition of nickel,but at the same time it also forms a sedimentary layer that is loose and easy to dissolve.Properly increasing the temperature favors the appearance of nucleation rings and dissolved peaks in the CV curve.The change in the direction of potential scanning in the CV curve resulted in the change in the structure of nickel deposits during the deposition process at-1.4 V,resulting in partition dissolution in the dissolution process,and the partition phenomenon in the dissolution process became more and more obvious with the increase of temperature.