Compounds were identified by comparing the observed retention times and mass spectra with those of respective standards prepared from commercial reagents/gases, and were quantified based on the calibration curves (SI Appendix, Fig. ). The obtained data were used to calculate the mole fractions of target compounds in the sample gas, which were then multiplied by the amount of gas-phase CO2 plus H2 -the predominant gas species-in the reaction vessel to determine the yield of each target (Fig. and). The amount of CO2 was calculated based on the mass of CO2 in the reaction vessel considering the dissolution of CO2 in the aqueous sample solution , whereas that of H2 was quantified via the GC measurement described below.