Proton conduction in polyhydroxy hydrogensulfated fullerenes

Proton conductivity of polyhydroxy hydrogensulfated fullerene C-60(OSO3H)(x)(OH)(y) (x similar to 6, y similar to 6), and partially hydrolyzed polycyclosulfated fullerene, C-60(OSO2O)(6-z)(OSO3H)(z)(OH)(z) (z < 1), was investigated. The ac impedance measurements revealed that these materials showed proton conductivities of 10 and 0.1 mS/cm, respectively, at room temperature. Those conductivity values are higher than that of a fullerenol-type proton conductor. This suggests that introduction of highly acidic groups, especially OSO3H, surrounding the fullerene cage leads to higher conductivity. The activation energy of the conduction in C-60(OSO3H)(x)(OH)(y) was estimated to be 0.35 eV from a variable-temperature conductivity measurement. The conductivity is constant for 15 h in a dry-gas condition, indicating that no water molecule drifts together with a proton in this material. It is thus suggested that protons in a polyhydroxy hydrogensulfated fullerene are transported by a hopping mechanism as is the case for fullerenol C-60(OH)(12). (C) 2002 The Electrochemical Society.