Influence of boric acid and Mn on electrolytic deposition of Co from low concentration sulphamate electrolytes

Abstract

The electrolytic deposition of Co from low concentration sulphamate electrolytes, containing manganese and boric acid, has been investigated. Growth of multilayered dendrite formations, comprising successive layers with very high Co or O content, is observed at high deposition potentials. For cobalt deposits, the obtained systems contain enormous amounts of incorporated hydrogen, ∼4200 ppm. The dependence of the hydrogen content remaining after thermal treatments at different temperatures suggests the presence of two types of bonded hydrogen. Cyclic voltammetry (CVA) has been used to study the electrode processes by sweeping the potential to different values. Some unexpected effects are established in the cathodic part of the CVA curves, related to an abrupt decrease in hydrogen evolution current and its subsequent oscillations at this lower value. The apparent contradiction between the huge amounts of incorporated hydrogen and the low cathodic currents of hydrogen evolution is explained by the reduced share of recombinant hydrogen at the expense of its absorption in the bulk of the deposit.