The Limiting Role of Iodide Oxidation in <i>cis</i>-Os(dcb)₂(CN)₂/TiO₂ Photoelectrochemical Cells

Abstract

Porous nanostructured photoanodes prepared from colloidal solutions of DeGussa or sol−gel processed TiO2 material have been derivatized with cis-M(dcb)2(CN)2, where M = Ru(II) or Os(II) and dcb is 4,4'-(COOH)2-2,2'-bipyridine. When employed in a regenerative solar cell with iodide donors, cis-Ru(dcb)2(CN)2/TiO2 converts absorbed photons to electrons nearly quantitatively while cis-Os(dcb)2(CN)2/TiO2 does not. In-situ time-resolved diffuse reflectance measurements reveal a sluggish iodide oxidation rate is responsible for the low photocurrent efficiency of cis-Os(dcb)2(CN)2/TiO2. Transient absorption measurements support this conclusion and allow full wavelength characterization of the charge-transfer processes.