ELECTROCHEMICAL INTERCALATION OF CATIONS INTO AN AMORPHOUS WO3 FILM AND ACCOMPANYING CHANGES IN MASS AND SURFACE-PROPERTIES

The electrochemistry of electrodes coated with amorphous WO3 film in p ropylene carbonate containing 0.1 M LiClO4, NaClO4, KPF6 or tetraethyl ammonium (TEA) perchlorate was examined. The surface density of redox- active sites on the WO3 film coated electrode is larger for smaller ca tions (Li+ > Na+ > K+). The charge transfer rate was also faster for s maller cations. In the KPF6 solution, the solvophilicity of the film s urface increased with potential cycling, while no significant changes were observed in the LiClO4 solution and NaClO4 solution. In the LiClO 4 solution, an apparent mass increase during cation intercalation, est imated using an AT-cut quartz crystal resonator, was roughly in agreem ent with the mass number of Li+. However, in the NaClO4 solution, an a pparent mass increase was significantly larger than the mass number of Na+; this may be caused by stress generated by intercalation of the m assive cation. Electrochemistry was not observed in the TEAClO(4) solu tion. Proton intercalation was not observed in the TEAClO(4) solution even in the presence of water (1.5 wt%), but was observed in the prese nce of CF3COOH (10 mM).