Potentiostatic Co-deposition of Nickel and Graphite Using a Composite Counter Electrode

Abstract

Nickel and graphite was potentiostatically co-deposited using a composite nickel-graphite composite counter electrode (CCE) with tunable-friability. This was done to achieve steady introduction of graphite into the electrolyte without intermittent mechanical infusion and stirring, thus facilitating a potentiostatic deposition route and promoting homogeneity of deposition. Graphite electrodes were produced at densities of 0.920, 1.026 and 1.188 g/cm3 and their suitability for constitution in a HCE assessed. The surface area of the nickel component of the HCE was varied from 100% to about 60 and 30% surface area and combined with the graphite electrode to form HCE constitutions designated as triplet, doublet and singlet respectively. Deposition was done for about 8 hours in 1 M NiSO4 using the different HCE constitutions, an Ag/AgCl reference electrode and a custom deposition head which served as the working electrode. The mechanism of graphite electrode unraveling was observed to be the formation of oxygen and CO2 due to oxidation reactions at the HCE. Graphite electrode of density 0.920 g/cm3 was selected for the HCE due to its extensive surface porosity, a characteristic determined as favourable to the mechanism of electrode unraveling. Co-deposition of graphite with nickel was observed to increase as nickel surface area was reduced from the triplet to singlet. SEM micrographs show partially and fully embedded graphite particles in the nickel matrix while the presence of nickel and graphite was affirmed.