Electrochemical investigation of the electron-transfer kinetics and energetics of illuminated tungsten oxide colloids

Electrochemical charge collection techniques were used to study the effects of platinization and reduction on the electron-transfer (et) kinetics and energetics of illuminated tungsten oxide colloids. From the mediated charge collection experiments, the quasi-Fermi level for electrons, nE/sub F/*, was found to be +0.33 V vs. NHE (pH O) for WO/sub 3/ and shifted to +0.21 V for the reduced (H/sub x/WO/sub 3/) and platinized (Pt/WO/sub 3/) tungsten oxides. The platinization of WO/sub 3/ also caused it to be irreversibly reduced. Silica particles coated with a monolayer of WO/sub 3/ displayed an nE/sub F/* which was 170 mV negative of that for WO/sub 3/. The photocurrent transients for direct et to a collector electrode were potential dependent and were used to measure k/sup 0/, the standard heterogeneous rate constant for et, by using a previous treatment derived for iron oxides. The reduction of WO/sub 3/ decreased k/sup 0/, while platinization slightly increased it.