Photoelectrochemical measurements. The photoelectrochemical measurements were conducted using a CHI 760E and SP-300 BioLogic potentiostats in a typical 3-electrode system with a Pt wire as counter electrode, an Ag/AgCl (1.0 M KCl, 0.222 V vs. SHE) as reference electrode and film photoanodes as working electrodes with geometric irradiation area of 0.5 cm 2 . A 150 W Xe lamp (L.O.T.-Oriel) equipped with a KG-3 (LOT-Quantum Design) heat-absorbing filter and an AM 1.5G filter was employed as light source (light power intensity 100 mW cm -2 ). The electrolyte was 0.5 M aqueous sodium borate, pH = 9.0. All electrodes were illuminated from the backside (through the FTO glass) unless noted otherwise.