For photocatalyst deposition, 2 mg of RhCrOx-Al:SrTiO3 was added to 200 μL of IPA and ultrasonicated for about 1 min until the catalyst was well-dispersed. This catalyst mixture was drop-casted onto the carbon paper in 4 equal layers (50 μL per layer), with the sheets being allowed to dry between each successive layer. 2 μL Nafion solution was diluted in 50 μL IPA and then drop-casted onto the sheets. The sheets were then dried at 338 K overnight (Supplementary Fig. ).