ELECTROCHEMICAL MICROGRAVIMETRY OF C-60 FILMS

Mass changes of C-60 films, which are prepared on electrodes by casting, during redox processes in acetonitrile were examined by means of quartz crystal microbalance technique. In the case where tetra-n-butylammonium perchlorate was used as a supporting salt, frequency decrease indicating mass increase corresponding to cation doping was observed during the first and second reduction processes. These doping processes were found to be reversible, though the irreversible and gradual mass decrease owing to C-60 dissolution was observed during continuous potential cycling. A fraction of the dissolved C-60 anion was deposited on the electrode again by the reoxidation. In the third reduction process, dramatic increase in the frequency indicating dissolution of C-60 was observed. In the case where lithium perchlorate or sodium perchlorate was used as a supporting salt, dramatic and irreversible frequency increase and deterioration of electrochemistry were observed even in the first reduction process. Therefore, C-60 anion is soluble in those solutions. Dependence of the stability of the film electrochemistry on cation species in acetonitrile was thus found to arise predominantly from difference in solubility of the cation fulleride salt.