Identification of Processes that Occur after Reduction and Dissolution of C₆₀ Adhered to Gold, Glassy Carbon, and Platinum Electrodes Placed in Acetonitrile (Electrolyte) Solution

Microcrystals of C₆₀(solid) may be adhered to glassy carbon, gold, and platinum electrodes. When the electrodes containing C₆₀(solid) are placed in acetonitrile (0.10 mol L^-1 Bu₄NClO₄) and the potential is scanned or stepped to significantly negative potentials, very fast dissolution processes of the kind C₆₀(solid) + ne^- →^fast C₆₀^n-(soln) (n = 3-5) occur. In contrast, one- and two-electron reductions only lead to a minor level of dissolution of C₆₀^- and C₆₀^2-. Electrochemical quartz-crystal microbalance studies on gold electrodes revealed that C₆₀^2-(solid) and C₆₀^-(solid) are intermediates in the n ≥ 3 reduction-dissolution processes and that a range of adsorption and precipitation steps occur when the dissolved material is oxidized back to C₆₀(solid). The exact details of the mechanism of the process that occur after reduction of C₆₀(solid) to dissolved C₆₀^n-(soln) (n = 3-5) under conditions of cyclic voltammetry depend on the scan rates, electrode material, and switching potentials employed. However, under carefully chosen conditions at a glassy carbon electrode, reaction schemes of the kind C₆₀(solid) + 5e^- → C₆₀^5-(soln) and C₆₀^5-(soln) ⇌^-e-_+e- C₆₀^4-(soln) ⇌^-e-_+e- C₆₀^3-(w/ad) ⇌^-e-_+e- C₆₀^2-(w/ ad) ⇌^-e-_+e- C₆₀^- (w/ad) are operative, where the symbol "w/ad" represents weak adsorption. However, the strength of adsorption increases on the order of C₆₀^- ≫ C₆₀^2- > C₆₀^3- > C₆₀^4- > C₆₀^5-, so that strong adsorption and even solid formation occur under other conditions and only fully surface confined C₆₀(solid) could be detected. The relationship between dissolution, adsorption, and surface attachment processes that accompany the voltammetry of C₆₀ has been identified.