The photoelectrochemical performance of the photocathodes was evaluated in a three-electrode configuration using a BioLogic SP-200 potentiostat under irradiation from simulated AM 1.5 G illumination, calibrated using a silicon diode from PV Measurements, Inc. (100 mW cm -2 ). A 1 M H2SO4 (pH 0) solution was used as the electrolyte. The reference electrode was Ag /AgCl (sat'd KCl), and a Pt wire was used as the counter electrode. Before measurement, the electrolyte was sparged with N2 for at least 30 min to remove dissolved oxygen. The photocathode area was defined using epoxy (Loctite 9461) and the active area was determined by counting pixels using the image processing software gimp. The onset potential was estimated by extrapolating the steep rise of the photocurrent in the current density-voltage plots to the voltage axis and the corresponding intercept was used as the onset potential. The conversion between potentials vs. Ag/AgCl and vs. RHE was performed using the equation: E (vs. RHE) = E (vs Ag/AgCl) + 0.059 V × pH + 0.197 V (EAg/AgCl) Incident photon-to-current efficiency (IPCE) was measured on a home-built IPCE system featuring a halogen light source with double monochromator and white light bias. The IPCE was measured in a three-electrode configuration using Ag/AgCl (sat'd KCl) reference electrode and Pt wire as the counter electrode at 0 V versus RHE in 1 M H2SO4 (pH 0) at 5 nm wavelength intervals. To compare the wavelength dependent change of the IPCE at different bias potentials, the IPCE values from the measurement at 0.05 V vs RHE was normalized (multiplied) to reach the same value at 540 nm as for the measurements at more negative applied potentials.