Despite Ni still being present in a higher concentration than Pt in the HGM/CNx|Pt samples (0.03% m/m) the activity is far lower, and it is expected that this is a consequence of the degradation of the catalytically active Ni2P species. This result also highlights the versatility and robustness of the Pt cocatalyst as it can be applied in various pH environments and would therefore be applicable to a wider range of substrates requiring different pre-treatment conditions. The performance of the HGM/CNx composites in a more realistic system mimicking realworld conditions was assessed using a large PVC reactor (217 cm 2 , 1.5 L) with a Plexiglas window to allow for vertical irradiation. The volumetric and areal concentrations of the floating composite from the small reactor experiments were maintained at 12 mg mL -1 and 12 mg cm -2 in this larger system with a fluid volume of 217 mL and depth of 1 cm. The areal activity HGM/CNx|Pt composite marginally declined over 10 consecutive trials in both EG (Figure ) and pre-treated PET (Figure ), with activities reaching minimum values of (85.2 ± 14.3)% and (93.4 ± 11.4)% of the initial activity, respectively (Table , ESI). The composite recovery was consistent across all triplicates over 10 cycles, with an average of (68.2 ± 6.0)% (Table , ESI). The HGM/CNx|Ni2P composite demonstrated a much more significant decline in activity, reaching minimum values of (16.9 ± 2.8)% in EG and (36.8 ± 28.9)% in PET (Figure , Figure , ESI). The Ni content in the composite was measured before and after 10 photoreforming cycles to test whether loss of Ni2P might be causing the decline in activity, but it was found that the Ni content of the floating fraction increased by (0.31 ± 0.16)% wt. (Figure , ESI). The decrease in activity of the HGM/CNx|Ni2P catalysts over multiple cycles in basic conditions is therefore not directly related to the dissolution or loss of Ni but may be due to surface modification of the Ni2P, for example, the formation of a passivating aerial oxidation layer that may block the catalytically active sites. This finding is also consistent with previous investigations of CNx|Ni2P that determined Ni content remains similar before and after photocatalysis, while activity and P content decreases significantly as Ni-P and NiOx species are replaced with Ni(OH)2. The areal activity of floating HGM/CNx composites under the PR conditions studied compares favourably to similar conditions previously explored for immobilised CNx on glass panels. The maximum activity of the HGM/CNx|Pt composite (217 cm 2 , 2 h, 1 mol L -1 KOH, 25 mg mL -1 EG, ~5.4 mgCN x cm -2 ) was observed to be 1767 ± 136 µmolH 2 m -2 h -1 , whereas previously reported CNx|Pt panels (1 cm 2 , 20 h, 0.5 mol L -1 KOH, 25 mg mL -1 EG, 1.92 mgCN x cm -2 ) were found to exhibit 280 µmolH 2 m -2 h -1 areal activity. Possible reasons for the increased activity in the floating system may include increased surface density of CNx, greater surface area availability of CNx for PR reactions, or improved light harvesting. Initially, the floating HGM/CNx|Ni2P system also outperformed its panel-immobilised counterpart with a maximum areal activity of 255 ± 109 µmolH 2 m -2 h -1 (217 cm 2 , 2 h, 1 mol L -1 KOH, 25 mg mL -1 PET, ~5.4 mgCN x cm -2 ) compared to 52 ± 3 µmolH 2 m -2 h -1 (25 cm 2 , 20 h, 0.5 mol L -1 KOH, 25 mg mL -1 PET, ~1.92 mgCN x cm -2 ), though the activity of the floating HGM/CNx|Ni2P composite was found to decline substantially over 20 h (10 consecutive cycles), while the panel system maintained steady activity over 20 h. This may be due to the nature of the recycling process which routinely exposes the catalyst to oxygen after every recycle to introduce fresh substrate solution, allowing a passivation layer to form, while the panels were operated continuously in an anoxic environment. Nevertheless, clear benefits in areal activity were realised in using the floating HGM/CNx system on free supports compared to CNx on static panel supports.