The second channel was used in a 2-electrode configuration between the same counter electrode and an additional platinum wire that was placed just underneath the working electrode. Prior to the OCP measurement (using the first channel), an electrolysis was carried out using the second channel for 30 min, which ensured saturation of the electrolyte solution with H2 in the vicinity of the Sb2Se3 photocathode surface (Figure indeed shows that the potential of the Sb2Se3, calculated according to Equation , is 0 VRHE in the dark). The light intensity dependence of the photocurrent measurement was performed at 0 VRHE using a three-electrode system. For both measurements, an array of nine white light diodes was used (SP-12-W5, cool white Luxeon Rebel) controlled by a Keithley power source (PSW4323).