Chemical forms of cobalt(0) related to polarogrphic and voltammetric catalytic hydrogen currents

The mechanism of catalytic hydrogen evolution at a mercury electrode in buffer solutions containing both bovine serum albumin (BSA) and Co(II) or Co(III) is discussed on the basis of the amount of Co(0) formed on the electrode as well as the solubility of the Co(0) species. An appropriate potential was times t, in ammonia buffer solutions in the presence of Co(III). After the mercury drop was washed with 0.1 M ammonia buffer (pH 9.3) and 1 M hydrochloric acid or concentrated hot hydrochloric acid, the amount of cobalt remaining in and/or on the mercury drop was determined by flameless atomic absorption spectrometry. Amalgamation of Co(0), which is insoluble in the ammonia buffer and 1 M hydrochloric acid, was formed on the electrode, regardless of the electrolysis potential, when t was short. With increase of t, Co(0) changed its characteristics, yielding a Co(0) species Co(0)_{Group 2}] soluble in 1 M hydrochloric acid but insoluble in the buffer, even though the time required for the change depended on the electrolysis potential. It is demonstrated that Co(0)_{Group 2} plays an important role in the appearance of such catalytic hydrogen currents as the first and second Brdička currents, the P-current of Anzenbacher and Kalous, and i_c of Kolthoff and Kihara.