Measurement and prediction of CO2 solubility in organic electrolytes for high pressure CO2 reduction

Abstract

The electrochemical CO2 reduction reaction (CO2RR) to organic products is becoming increasingly important. Here, organic electrolytes play a crucial role, since adding salt to organic solvent allows an increase in the current density, and together with supercritical CO2 organic electrolytes suppress hydrogen evolution during the CO2RR. Since the selectivity to organic products depends on the CO2 content, CO2 solubility was investigated in organic electrolytes at different salt concentrations, pressures (up to 150 bar), and temperatures (25 °C and 70 °C). These organic electrolytes included the mixtures NaI-methanol, KSCN-methanol, (C2H5)4NBF4-acetonitrile, and (C4H9)4NBF4-acetonitrile. Afterwards, electrolyte Perturbed-Chain Statistical Associating Fluid Theory (ePC-SAFT) was applied to predict the CO2 solubility in these organic electrolytes. The results showed that i) CO2 solubility decreased with increasing temperature and salt concentration, ii) dissolving CO2 may cause a precipitation of salts, and that iii) ePC-SAFT allowed to qualitatively model the CO2 solubility in organic electrolytes