Entropy Drives Accelerated Ion Diffusion upon Carbon Dioxide Expansion of Electrolytes.

Carbon dioxide-expanded liquids, organic solvents with high concentrations of soluble carbon dioxide (CO) at mild pressures, have gained attention as green catalytic media due to their improved properties over traditional solvents. More recently, carbon dioxide-expanded electrolytes (CXEs) have demonstrated improved reaction rates in the electrochemical reduction of CO, by increasing the rate of delivery of CO to the electrode while maintaining facile charge transport. However, recent studies indicate that the limiting behavior of CXEs at higher CO pressures is a decline in solution conductivity due to reduced polarity, leading to poorer charge screening and greater ion pairing.

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

Electrolyte conductivity contributes to the efficiency of devices for electrochemical conversion of carbon dioxide (CO) into useful chemicals, but the effect of the dissolution of CO gas on conductivity has received little attention. Here, we report a joint experimental-theoretical study of the properties of acetonitrile-based CO-expanded electrolytes (CXEs) that contain high concentrations of CO (up to 12 M), achieved by CO pressurization. Cyclic voltammetry data and paired simulations show that high concentrations of dissolved CO do not impede the kinetics of outer-sphere electron transfer but decrease the solution conductivity at higher pressures.

Distinguishing the mechanism of electrochemical carboxylation in CO eXpanded Electrolytes.

We shed light on the mechanism and rate-determining steps of the electrochemical carboxylation of acetophenone as a function of CO concentration by using a robust finite element analysis model that incorporates each reaction step. Specifically, we show that the first electrochemical reduction of acetophenone is followed by the homogeneous chemical addition of CO. The electrochemical reduction of the acetophenone-CO adduct is more facile than that of acetophenone, resulting in an Electrochemical-Chemical-Electrochemical (ECE) reaction pathway that appears as a single voltammetric wave.

Electrochemical properties and C-H bond oxidation activity of [Ru(tpy)(pyalk)Cl] and [Ru(tpy)(pyalk)(OH)].

[Ru(tpy)(pyalk)Cl]Cl (pyalk = 2-(2'-pyridyl)-2-propanol) was synthesized and characterized crystallographically and electrochemically. Upon dissolution in water and acetonitrile, [Ru(tpy)(pyalk)Cl]Cl was found to form [Ru(tpy)(pyalk)Cl]+ and [Ru(tpy)(pyalk)(OH)]+, respectively. The Ru(ii/iii) couple of [Ru(tpy)(pyalk)Cl]+ was found to be relatively low compared to that of other Ru complexes in acetonitrile, but the Ru(iii/iv) couple was not significantly different than other Ru complexes bearing anionic ligands.