Cathodic dissolution behavior of an aluminum wire electrode in solutions containing borate and sulfate ions

Dissolution of Al wire electrodes due to local alkalization induced by the hydrogen evolution reaction under conditions of cathodic polarization in neutral solutions containing K2SO4 and borate ions was examined using resistometry. The dissolution rate increased almost linearly with increase in the cathodic current, and about 30–40% of OH− ions generated by the hydrogen evolution reaction was used to form Al(OH)4− ions. The dissolution depth calculated from the resistance change increased linearly with the increase in concentration of K2SO4 ions. In K2SO4 solutions, Al dissolved uniformly and provided a porous surface. In a mixture of K2SO4 solution and borate solution, however, non-uniform dissolution occurred due to formation of large pits. Such non-uniform dissolution is due to the buffer capacity of borate ions in the weakly alkaline range.