The Pt catalyst was deposited using a pulsed photo-electrodeposition method with 10 mM H2PtCl6 (ACS reagent, ≥ 37.50% Pt basis, Merck) in 2 M HCl. Under 1 sun illumination, the voltage was stepped between OCV (for 5 s) and a negative bias (for 0.25 s) that reduced Pt onto the surface of the device.