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 degrees , for the ferrocene/ferricinium electron-transfer reaction. Casting these data in Arrhenius form yields a value of k degrees (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 linear through Tc. This is the first sub-Tc electrochemistry of any kind on a Hg-based superconductor and demonstrates the ease with which kinetic data can be obtained for these very high-Tc materials, opening the way for the routine study of a range of electron-transfer reactions as novel probes of the superconducting state.
Green
Stephen J
SJ
School of Chemistry, University of Exeter, Stocker Road, UK. Stephen.j.green@exeter.ac.uk
Le-Poul
Nicolas
N
Edwards
Peter P
PP
Peacock
Graeme
G