While we have previously shown that FDh produces formate with nearly 100% FE under pure CO2 on ITO, the reduced FE under low CO2 concentrations can be tentatively attributed to the residual background reduction of the metal oxide electrode. This can be observed in the absence of enzymes with no liquid or gaseous products being detected by Ion or Gas Chromatography, respectively (Figure ) at current densities that match well with the unattributed FE under low CO2 concentrations. As the reduction products of ITO cannot be quantified by liquid or gas phase techniques during electrolysis with enzymes a FE is not reported for this reaction.