Evidence for nucleation-growth, redistribution, and dissolution mechanismsduring the course of redox cycling experiments on the C-60/NBu4C60 solid-state redox system: Voltammetric, SEM, and in situ AFM studies

The electrochemical reduction of solid C-60 abrasively attached in the form of microcrystals to graphite and glassy carbon electrode surfaces and then immersed in acetonitrile containing 0.1 M NBu4PF6 or NBu4ClO4 as the elect rolyte has been studied. Voltammetric responses observed after the initial stages of redox cycling experiments, when redistribution processes occur, a re consistent with those observed previously for so-called "film" deposits. The characteristic "steady-state" shape of the solid-state voltammetric re sponse with a large potential gap between reduction and reoxidation respons es is shown by chronoamperometric experiments to be associated with the pre sence of a nucleation and growth-type mechanism. The initial three reductio n processes of C-60 attached to the electrode surface, which lead to the ch emically reversible formation of only slightly soluble C-60(-) and C-60(2-) and finally to the loss of the soluble C-60(3-) have been followed by ex s itu SEM and in situ AFM experiments. The extent of the electrochemical conv ersion is shown to depend strongly on the crystal size, with larger crystal s being affected only at the solid-liquid interfacial region. Evidence for stochastic processes further supports the proposed nucleation and growth-ty pe mechanism. Crystal redistribution processes also are identified by the A FM measurements.