The Selectivity of CO2 Reduction By the Solvated Electron Tuned By the Acid Scale

Abstract

The electrified plasma/liquid interface (PLI) induces the CO2 reduction (CO2R) by mediation of the solvated electron. Recent theoretical analysis of the chemical reaction network (chemical mechanism) revealed a 100% faradaic efficiency for CO2R [1] provided that the liquid surface was a flowing electrolyte; however, the theoretical analysis did not consider the proton concentration as a chemical variable, or the pH of the electrolyte so to speak, disabling to predict the distribution of products over the entire acid scale. For this reason, in this work, the proton has been categorically considered as a reactant and an essential variable for the dynamical model describing the CO2R via electrified PLI.Two new routes toward formic acid production are proposed namely the disproportionation-like (via-2) and radical cross-combination (via-3) reactions, see figure 1. Both consume the radical H formed by the scavenging of the solvated electron by the proton. The computational results reasonably matched the concentration ratio formate to oxalate around 3.0 for pH 2.45, which features the physical experiments [2]. This ratio would represent 25% selectivity toward formate at pH 2.45 for a flowing-electrolyte experiment. With this reasonably assertive mechanism, it was possible to predict that, at the same conditions of flowing electrolyte, an extremely acid pH (~1) would increase the selectivity toward formate, between 46 and 90% repectivelly for via-2 and via-3.Fig 1. Chemical reaction networks are shown in the LHS, and the predictions on the concentration ratio oxalate to formate are shown in the RHS for each path of formate synthesis (via–3 and via–2) and both combined.