After GC measurements of the headspace samples, corresponding chromatograms are obtained, from which the absolute peak area for the hydrogen peak can be obtained (see Figure ) Based on the calibration measurements, a linear calibration function can be calculated (see Supplementary Figure ). Using this function, the peak area can be converted to vol% H2 in the headspace. In case of the example shown in Figure , the H2 concentration is 0.03 vol%. In analogy to the calculation above, we can convert this to the catalytic activity, considering the headspace volume (1.3 mL) and the amount of used catalyst (2.7 mg), giving 6 μmol(H2) g(catalyst) -1 .