Photoelectrochemical Behavior of a Molecular Ru-Based Water-Oxidation Catalyst Bound to TiO2-Protected Si Photoanodes

A hybrid photoanode based on a molecular water oxidation precatalyst was prepared from TiO 2 -protected n - or p + -Si coated with multiwalled carbon nanotubes (CNT) and the ruthenium-based water oxidation precatalyst [Ru IV (tda)(py-pyr) 2 (O)], 1(O) (tda 2– is [2,2′:6′,2″-terpyridine]-6,6″-dicarboxylato and py-pir is 4-(pyren-1-yl)- N -(pyridin-4-ylmethyl)butanamide). The Ru complex was immobilized by π–π stacking onto CNTs that had been deposited by drop casting onto Si electrodes coated with 60 nm of amorphous TiO 2 and 20 nm of a layer of sputtered C. At pH = 7 with 3 Sun illumination, the n -Si/TiO 2 /C/CNT/[ 1 + 1(O) ] electrodes exhibited current densities of 1 mA cm –2 at 1.07 V vs NHE. The current density was maintained for >200 min at a constant potential while intermittently collecting voltammograms that indicated that over half of the Ru was still in molecular form after O 2 evolution.