Charge transfer rate constants for the reduction of cobaltocenium at accumulated n-Si electrodes

A theoretical description of heterogeneous charge transfer rate constants has been developed for accumulated semiconductor electrodes in contact with outer sphere redox couples. Analysis of the rate constants using a Fermi Golden Rule formalism in a non-adiabatic electron transfer framework has facilitated a theoretical comparison between the rate constants of metal and accumulated semiconductor electrodes in contact with a common electrolyte-redox couple solution. Chronoamperometric measurements of n-Si electrodes in contact with CH₃OH-cobaltocenium (CoCp2)⁺-CoCp₂ have been performed to investigate these predictions experimentally. A standard rate constant, k^o, of (2-4) × 10^-2 cm s^-1 was obtained for n-SiAZH₃OH-CoCp₂^+/0 contacts, while the CoCp₂^+/0 redox couple was found to be electrochemically reversible (k^o > 0.1 cm s^-1) at Hg electrodes under the same conditions.