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

Abstract

A hybrid photoanode based on a molecular water oxidation precatalyst was prepared from TiO2-protected n- or p+-Si coated with multiwalled carbon nanotubes (CNT) and the ruthenium-based water oxidation precatalyst [RuIV(tda)(py-pyr)2(O)], 1(O) (tda2– 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 TiO2 and 20 nm of a layer of sputtered C. At pH = 7 with 3 Sun illumination, the n-Si/TiO2/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 O2 evolution.