The photoelectrochemical performance of the photocathodes was evaluated using a BioLogic SP-200 potentiostat. This assessment followed a three-electrode setup, with simulated AM 1.5G illumination provided and calibrated to 100 mW cm -2 (1 sun) using a silicon diode sourced from PV Measurements, Inc. The electrolyte used was a 1 M H2SO4 solution with a pH of 0. The threeelectrode configuration consisted of an Ag/AgCl reference electrode immersed in a 3 M KCl solution, a counter electrode made of freshly cleaned Pt wire, and the photocathode serving as the working electrode. Cyclic voltammetry (CV) measurements were conducted at a scan speed of 10 mV s -1 . The scans were performed by sweeping from positive to negative potential and then back to positive potential. The exact onset potential value was defined by extrapolating to zero current from the oxidative sweep at the HER peak. To define the photocathode area, epoxy (specifically Loctite 9461) was applied around an O-ring with an inner diameter of 7 mm and placed on the sample's surface. For measurements of incident photon-to-current efficiency (IPCE), a custombuilt IPCE system was utilized. This system included a halogen light source, a double monochromator, and white light bias generated by an LED. IPCE measurements were also conducted within the aforementioned three-electrode configuration, maintaining a potential of -0.2 V versus RHE (Reversible Hydrogen Electrode). These measurements were performed with 5 nm wavelength intervals and a 1% white light bias.