Modelling of solid-state, dissolution and solution-phase reactions at adhered solid-electrode-solvent (electrolyte) interfaces: Electrochemistry of microcrystals of C₆₀ adhered to an electrode in contact with dichloromethane (Bu₄NClO₄)

Frequently, dissolution processes accompany voltammetric investigations of solids adhered to electrode surfaces that are placed in contact with a solvent (electrolyte). However, rarely have such processes been modelled in order to determine what thermodynamic and kinetic information may be deduced. An unusual combination of factors associated with a very low rate of dissolution of C₆₀ particles immobilised on glassy carbon and gold electrodes and a very rapid rate of dissolution of reduced C₆₀^- made it possible to investigate and model both solid-state and solution-phase aspects of the voltammetry of C₆₀ that occurs at an electrode-C₆₀-dichloromethane (electrolyte) interface. When an electrode containing adhered C₆₀ is placed in dichloromethane containing 0.10 mol l^-1 of n-Bu₄NClO₄, the reduction mechanism can be explained in terms of the scheme: Alternatively, a square scheme involving C₆₀^-(solid) may be operative in the initial stage of the reduction. The rate of dissolution of C₆₀ from a gold electrode surface at the open circuit potential and potentials prior to reduction was measured by the quartz crystal microbalance technique and shown to be dependent on the solubility of C₆₀ in dichloromethane and the rate of diffusion of dissolved material into the bulk solution. Results were in good agreement with a simple theory developed to model the dissolution process. In contrast, after reduction of C₆₀ to C₆₀^- in the solid state, restrictions based on solubility are eliminated and dissolution of adhered solid becomes very rapid. This stage of the dissolution process was studied by cyclic voltammetry, single- and double-potential-step methods, chronocoulometry and microgravimetry, and again has been modelled.