The individual plots of HGM/CNx|Ni2P areal activity in the small reactor recyclability trials can be found in the supporting information (Figure , ESI) with scales that more clearly show the decline in activity from run to run. The decrease in activity exceeds the composite mass loss over 10 cycles, pointing to a decline in the photoreforming activity of the Ni2P cocatalyst. This is especially evident in the cellulose substrate solution (Figure ) where the activity rapidly drops to 0 over only 3 runs. This is likely due to dissolution of the Ni2P co-catalyst which has poor stability in acidic environments such as the pH 5 pre-treated cellulose solution. Measuring the Ni content of the composite by ICP-OES after 10 cycles in the pre-treated cellulose solution yielded (0.056 ± 0.005)% m/m compared to (1.56 ± 0.01)% after 10 cycles in EG or pre-treated PET solution, confirming the difference in stability between the different pH environments.