The local pH environment can also separately influence the energetics of different CO2 reduction products. For catalysts capable of producing only CO and H2, the suppression of H2 can lead to high CO selectivities. On a Ag catalyst CO formation under alkaline conditions has been also been observed to be produced almost immediately following the equilibrium potential of -0.11 V vs RHE , indicating that the reaction itself is improved. The behaviour of CO formation on Cu also differs from that of a more neutral H-cell environment. In H-cell tests CO selectivities of >20% are observed on Cu and Cu-derivatives only at very low current densities (<5 mA/cm 2 ) before being supplanted by CO2 reduction to methane, ethylene and ethanol. Under alkaline conditions performed in a gas-diffusion layer, high CO selectivities appear over a much broader range (0-200 mA/cm 2 ) . This suggests that the binding energy of CO on Cu may be weakened under alkaline conditions, promoting faster desorption of the formed *CO intermediate more than under neutral conditions. The selectivity towards CO does eventually decrease in favour of higher order products similar to what is observed in an H-cell, but at much higher overall current densities.