For the blank measurements, i.e. in the absence of HQ or the photosensitizer, the total volume of 5 mL was maintained by the addition of CH3OH. The beam of the diode laser was directed to the working electrode to measure the photocurrents. Prior to use, the working electrodes were polished on wet grinding paper (GRIT 800, Buehler) for 1 min, then sonicated for 20 sec in deionized water and dried in air.