The concentration of glycerol in the cathodic chamber after 48 and 72 hours from the beginning of the experiment were 39 mM and 72 mM, respectively. Glycerol permeates through the BPM regardless of whether electrolysis was occurring. The NMR spectra used to quantify glycerol crossover are shown in Figure . The permeation rate of glycerol through the BPM was relatively constant in time and calculated to be 6.7 ± 0.4 µmol cm -2 h -1 from the slope of the NMR-determined concentrations shown in Figure . The effects of this loss of glycerol on the cell potential over the duration of the experiments are small compared to the electrocatalytic consumption of glycerol by anode.