No.11（2016）5.Inhibition mechanism of hydrogen evolution reaction in the nickel citrate electroplating

Tadashi Doi

  In response to the strict regulations on the discharge of boron that have been established for environmental protection in Japan, the authors developed a new nickel electroplating bath known as a “citrate bath” using citric acid instead of boric acid in the Watts bath. The citrate bath offers an excellent, practical and more environmentally friendly plating method in decorative and anti-corrosion applications. The citrate bath exhibits the same level of cathode current efficiency and pH buffering capacity of the bath as the Watts bath. To clarify the acting mechanism of the hydrogen evolution reaction in the citrate bath, we investigated the relationship between the electroplating properties and the form and existing state of the complexes formed with the nickel ions using citric acid and acetic acid. These results indicate that abundant nickel ions are present in the citrate bath and that nickel electrodepositing from the nickel citrate complexes is carried out. The results also suggest the possibility that the citrate bath results in inhibition of the hydrogen evolution reaction, resulting in a high cathode current efficiency and excellent pH buffering capacity of the bath.

Keywords
Citric acid, Nickel electroplating, Nickel citrate electroplating bath, Hydrogen evolution reaction, Nickel citrate complexes

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