Sub-Tc electron transfer at the Hg-HTSC/liquid-electrolyte interface.

The cyclic voltammetry of ferrocene (CpFeCp) adsorbed as a monolayer of CpFeCpCO2(CH2)8SH, self-assembled onto the Hg-based high-temperature superconductor Hg0.8Re0.2Ba2Ca2Cu3O10 (Tc = 134 K), via an ultrathin (3.1 nm) Ag film, has been performed in liquid electrolyte (16:7:1 EtCl/THF/2-MeTHF; 0.2 M LiBF4) at a range of temperatures spanning the superconducting transition. Kinetic analysis based on the Marcus density-of-states theory affords standard heterogeneous rate constants, k°, for the ferrocene/ferricinium electron-transfer reaction. Casting these data in Arrhenius form yields a value of k°(273 K) = 357 s-1, which is 10-fold lower than that previously reported for the same reaction at a metal electrode in a similar electrolyte, while the reorganizational energy of 0.92 eV for the superconductor interface is very close to that for the related metal interface of 0.95 eV. There is, however, no effect of the onset of superconductivity on the electron-transfer rate for this system; the Arrhenius plot is...