The confined macroporous structure also creates a unique chemical environment that controls the maximum amount of co-immobilised CA, in contrast to reported mesoporous ITO electrodes . Doubling the CA loading (200 pmol) led to a low FY of 36% over 10 h (123 µmolformate cm -2 ), whereas shortening the CPE duration to 2 h improved FY to 100% (65 µmolformate cm -2 ) (Fig. ). Due to the non-redox active nature of CA, and when there is sufficient CA such that CO2, H + and HCO3