Unexpected stabilization of a simple cobalt(I) salt in acetonitrile at a glassy carbon electrode

It is shown that a simple electrogenerated cobalt(I) species of the type Co(BF4) can be stabilized on the time-scale of slow cyclic voltammetry, provided the use of both a glassy carbon working electrode and acetonitrile as solvent. Under these conditions, the reduction of CoII(BF4)2 and CoI(BF4) occurs, respectively, at −0.86 V and −1.16 V versus the saturated calomel electrode (SCE). Nevertheless, unlike CoI, the electrogenerated Co0 species is not stabilized. This zero-valent cobalt species leads rapidly to the inactive solid cobalt by nucleation. Studies of the peak current variation of both the reduction of CoII and oxidation of CoI as a function of both the scan rate and the cobalt(II) salt concentration have been performed to gain more insight about the nature of the cobalt(I) stabilization. It is particularly established that stabilization of CoI is a diffusion controlled process at scan rates higher than 0.1 V s−1 whereas adsorption phenomena, on the glassy carbon electrode, are involved at lower scan rates. Interestingly, the presence of bromide ions inhibits the stabilizing effect. More importantly, such a stabilization is not observed with other metals such as iron, nickel, copper, or zinc salts.