O by photogenerated electrons. The faster consumption of photogenerated electrons translates into diminished recombination of electron-hole pairs, and represents the basis for effective enhancement of photocatalysis at a-TiO2(400)-V SA (Figure ). The situation is very different for a-TiO2-Cu SA (Figure ) as the Cu-induced intragap states are centered at ca. +0.1 V vs. NHE (at pH 7). As compared to a-TiO2(400)-V SA , the thermodynamic driving force for the direct reduction of O2 is therefore diminished by ~0.6 V.