The various HGM/CNx composites prepared with different HGM:melamine ratios were assessed for their PR activity in small-vial (7.9 mL) solar PR trials. An amount of HGM/CNx was added to each vial based on the CNx content of the composite (Table ) such that the final concentration of CNx in each experiment was 1.5 mg mL -1 . A substrate solution containing 1 mol L -1 KOH and 25 mg mL , ESI). PR activity may also be affected by the type of deposition, in addition to the Pt surface loading, with chemical reduction producing stable metallic deposits that are not deactivated over time, as in photo-deposited Pt, possibly contributing to higher sustained activities. Based on its specific activity and floating fraction recovered after synthesis, the 1:3 HGM:melamine floating composite was selected as the HGM/CNx material used in all further PR experiments.