Scheme 3 indicates that 2 molecules of CO2 are generated during each cycle of the S2O8 2- /C2O4 2-autocatalytic reaction. To test this prediction, DEMS, a powerful operando method useful in real time monitoring of electrogenerated gaseous and/or volatile species, was used to detect CO2 produced by the autocatalytic reaction. Cyclic voltammetry was performed using a porous carbon cloth as the working electrode, while monitoring the mass spectrometer ion currents at m/z = 44 (ionized CO2, CO2 + ) and 22 (doubly ionized CO2, CO2 2+ ). Briefly, any CO2 generated by the autocatalytic reaction diffuses through the carbon cloth electrode, eventually partitioning out of the electrolyte phase into the DEMS sample inlet (see the SI for a more detailed description). In a set of control experiments, no signal associated with potential-induced CO2 generation was detected during CV scans between 0.1 and -0.5 V vs Ag/AgCl in: (i) a 0.1 M Na2SO4 background solution; (ii) a solution containing 0.1 M Na2SO4 and 0.5 mM Ru(NH3)6 3+ ; or (iii) a solution containing 0.1 M Na2SO4, 0.5 mM Ru(NH3)6 3+ and 100 mM C2O4 2-(Figure ). However, when a voltammetric scan was performed in a solution containing 0.5 mM Ru(NH3)6 3+ , 100 mM C2O4 , and 1.0 mM S2O8 2-, ionic currents for CO2 + (m/z = 44) and CO2 2+ (m/z = 22) were observed in the DEMS response, as shown in Figure and Figure . These observations unequivocally establish that CO2 is generated during the Ru(NH3)6 2+ catalyzed reduction of S2O8 2-in the presence of C2O4 2-.