Tuning the Polarity of Dinitrile-Based Electrolyte Solutions for CO₂ Electroreduction on Copper Catalysts

Abstract

The development of carbon dioxide electrochemical reduction (CO2ER) has mainly focused on aqueous electrolytes. However, the low solubility of apolar CO2 in polar water negatively impacts the electrochemical process, especially mass transport. Organic-based electrolytes, such as methanol, acetonitrile, and dimethylformamide, have been explored as an alternative due to increased CO2 solubility. Yet, insights into other organic electrolytes are scarce. Dinitrile solvents have decreased polarity in comparison to the mononitrile solvent acetonitrile and thus can potentially further increase CO2 solubility and advance the reaction’s performance. Herein, the novelty of dinitrile-based electrolytes for the application of CO2ER is explored. Acetonitrile, adiponitrile, and sebaconitrile were used to study the effects of a secondary nitrile group addition and the length of the aliphatic, nonpolar chain on salt solubility, electrolyte conductivity, and CO2 solubility. Electrochemical effects were evaluated through cyclic voltammetry (CV) and chronoamperometry (CA) measurements with copper (Cu) and copper oxide (CuO) commercial nanoparticle catalysts. DFT calculations were employed to further explore the CO2 interactions with the selected solvents. Finally, it was found that tuning the polarity of the nitrile solvent results in a profound effect on the physiochemical properties of the electrolyte solutions, markedly CO2 solubility and the CO2ER.

Mechanistic Basis of Conductivity in Carbon Dioxide-Expanded Electrolytes: A Joint Experimental–Theoretical Study

“…Prior findings from the literature show that, under conventional conditions, solution conductivity decreases linearly with decreasing ionic strength. 33 Thus, our findings in these CXEs contradict this expected behavior based only on ionic concentration. However, as previously stated, this is not the sole factor that contributes to conductivity, and thus other effects, identified by molecular dynamics simulations (vide infra), must also be taken into account.…”

“…This also appears to be the case with Et 2 O dilution; dilution of 4 blue points. 33 In addition to the slight deviation from linearity in the dilution-dependent conductivity data using Et 2 O, we also identified several other key insights. The more negative slope/ dependence of the conductivity-vs-concentration plot obtained for the case of dilution with Et 2 O can be superficially understood to arise due to the smaller dielectric constant of Et 2 O (4.27) in comparison to that of MeCN (36.64).…”

“…0.31 M. In the second regime, with pressures of CO 2 around 450 psi and greater, we measured a linear decrease in conductivity. Prior findings from the literature show that, under conventional conditions, solution conductivity decreases linearly with decreasing ionic strength . Thus, our findings in these CXEs contradict this expected behavior based only on ionic concentration.…”