The oxygen evolution was recorded by FireSting optical fiber oxygen meter (PyroScience, GmbH) in a home-made air-tight two-compartment cell with the oxygen collection efficiency as approximately 75%, which was estimated by a direct electrolysis using a Pt working electrode. The volume of the photoanode compartment was 5 mL. The oxygen concentrations are not corrected for the losses in the gaseous headspace. The electrolyte was purged with argon before the electrodes were illuminated under applied potential of 1.12 V vs. RHE. The incident monochromatic photon-to-current conversion efficiency (IPCE) was recorded using a photoelectric spectrometer (Instytut Fotonowy Sp. z o.o.) equipped with a tunable monochromatic light source provided with a 150W Xenon lamp and a grating monochromator with a bandwidth of ~ 10 nm. The value of photocurrent density was the difference between current density under irradiation and in the dark in steady-state conditions with a wavelength sampling interval of 10 nm. The IPCE value for each wavelength was calculated according to equation: