for AOx (Figure ). These current decreases are comparable to the ones obtained in the absence of the O2 scavenging system when purging the electrolyte with Ar to remove O2. When using paraformaldehyde as substrate, the catalytic current for glucose oxidation steadily decreases over time, which closely follows the pH drop from 7.1 to 6.7 due to the generation of formic acid (Figure ). Nevertheless, this pH and activity decay is on the time scale of hours.