For the Linear Sweep Voltammetry (LSV) measurements, an SP-300 potentiostat (BioLogic) and a 150 W Xe lamp (L.O.T.-Oriel) equipped with a KG3 heat filter and an AM1.5G filter with a light power density adjusted to ca. 100 mW cm -2 (1 sun) were used. Borate buffer (pH 9) was determined as the optimum electrolyte for all measurements. During the measurements, the solution was gently purged with molecular oxygen acting as an electron scavenger. Unless otherwise indicated, all electrodes were irradiated from the backside.