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By. Dr. S. Alec Watson, Dec 1990. During nickel electrodeposition, the anode provides electrical contact with the solution and distributes the current to the work being plated. In most cases, it is pointed out, the process uses nickel metal anodes that dissolve as the current flows and thereby replace the nickel ions discharged at the cathode, maintaining the concentration of nickel salts dissolved in the plating solution. Small insoluble anodes made of titanium with a thin coating of platinum have been used in decorative plating solutions to augment the current from the main soluble anodes arriving at deeply recessed areas. The insoluble anodes were placed adjacent to the recesses and supplied with current from a separate supply sufficient to increase the thickness of the nickel deposit within the recess to the required value. This technique suffers from three disadvantages: first, chlorine as well as oxygen can be evolved at the anode and must be evacuated because it is toxic; second, organic addition agents are consumed rapidly at the insoluble anode owing to its high potential; and third, the solution pH falls at the insoluble anodes owing to the discharge of hydroxyl ions -- if the current that passes to the insoluble anodes is more than 2 or 3% of the total current, the overall pH of the solution will fall, not rise, in use, thereby requiring adjustment with inconvenient nickel carbonate or hydroxide instead of sulphuric acid. These disadvantages can be overcome by the use of soluble anodes. Only soluble nickel anodes are considered further here.

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