The formate partial current density of CO2R by immobilized FDh (jformate, points, Figure ) in 1% and 10% CO2 purged solutions with N2 as the balance gas, unlike when purged with concentrated CO2 , was not affected by CA co-immobilization. Formate was the quantitative product as no other liquid or gas phase products (such as H2, CO or CH4) were detected by ion chromatography or headspace gas chromatography, respectively (for total and partial current densities from all experiments including controls see Table ). At 10% CO2, the co-immobilization of CA increased the jformate from -63 ± 17 µA cm -2 to -72 ± 37 µA cm -2 and at 1% the coimmobilization of CA decreased the jformate from -10 ± 4 µA cm -2 to -8 ± 4 µA cm -2 at -0.6 V vs SHE. The FE for HCOO -at -0.6 V vs SHE was 83 ± 8% at 10% CO2 and 54 ± 7% at 1% CO2.