The produced hydrogen was measured on an Inficon Fusion Micro gas chromatograph with a molecular sieve column (5Å) and a µTCD. Argon was used as the carrier gas. Before starting the measurements, the samples were placed in a one-component cell with a reference and a counter electrode. They were degassed for 30 to 40 minutes with argon, and three baseline measurements were done before each sample measurement. The operation pressure was between 1.020 and 1.030 bar and kept constant with a pressure control system. The calibration (and associated calculations) are seen and described in the supplementary information, Figure and Table .