Abstract In the potential region corresponding to the reduction of Co(OH) + to the metal, a catalytic polarographic current is observed in an ammoniacal buffer solution containing nitrite ion. In neutral unbuffered media, the catalytic current appears even on the limiting plateau of aquacobalt(II) reduction wave. The catalytic current is due to the reoxidation of an electrodeposited metallic cobalt to Co(II) by nitrite ion. The condition necessary for the catalytic reaction to proceed is the increase in pH at the electrode surface. It is shown that the hydroxide ion is produced as a result of the catalytic reaction.