Highly Stable Pt/CVD-Graphene-Coated Superstrate Cu2O Photocathode for Water Reduction

Here, we demonstrate a highly stable protected superstrate architecture Cu2O photocathode for water reduction. The Cu2O layer was electrodeposited on F-SnO2 (FTO) substrate via a modified method to obtain larger grains, 3.0–4.0 µm size owing to minimize the short-circuit current at the grain boundaries. Chemical vapor deposited (CVD) graphene being a robust material and also possessing the requisite properties (work function 4.6 eV and high conductivity) for cathode protection was coated on top of the device. Pt cocatalyst (30 nm) was deposited via e-beam evaporator on top of CVD-graphene to enhance the hydrogen evolution reaction (HER) kinetics at the electrode-electrolyte interface, also helped in blocking the microcracks in the graphene layer. The transparent FTO substrate enables back-illumination during the experiment, thereby allowing a non-transparent protective coating. This protected device shows stable photocurrent generation of ~2.5 mA cm−2 under one sun illumination in 1 M Na2SO4 electrolyte for one hour of the experiment.