Molecular origin of high free energy barriers for alkali metal ion transfer through ionic liquid–graphene electrode interfaces

In this work we study mechanisms of solvent-mediated ion interactions with charged surfaces in ionic liquids by molecular dynamics simulations, in an attempt to reveal the main trends that determine ion–electrode interactions in ionic liquids. We compare the interfacial behaviour of Li+ and K+ at a charged graphene sheet in a room temperature ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate, and its mixtures with lithium and potassium tetrafluoroborate salts. Our results show that there are dense interfacial solvation structures in these electrolytes that lead to the formation of high free energy barriers for these alkali metal cations between the bulk and direct contact with the negatively charged surface. We show that the stronger solvation of Li+ in the ionic liquid leads to the formation of significantly higher interfacial free energy barriers for Li+ than for K+. The high free energy barriers observed in our simulations can explain the generally high interfacial resistance in electrochemical storage devices that use ionic liquid-based electrolytes. Overcoming these barriers is the rate-limiting step in the interfacial transport of alkali metal ions and, hence, appears to be a major drawback for a generalised application of ionic liquids in electrochemistry. Some plausible strategies for future theoretical and experimental work for tuning them are suggested

Simulation of a Solvate Ionic Liquid at a Polarisable Electrode with a Constant Potential

In this article we discuss the nanostructure and calculated the capacitance of a solvate ionic liquid–electrode interfaces, where the electrode has a constant potential, and is thus inherently polarisable. Lithium ions from the lithiumglyme solvate ionic liquid are found within 0.5 nm of the electrode at all voltages studied, however, their solvation environment varies with voltage. Our study provides molecular insight into the electrode interface of solvate ionic liquids, with many features similar to pure ionic liquids. A comparison with previous studies of the same electrolyte using the fixed surface charge boundary condition is also illuminating, informing future computational studies of electrolyte–electrode interfaces.</div

Catalytic CO2/CO Reduction: Gas, Aqueous and Aprotic phase

The catalytic reduction of CO2/CO is key to reducing carbon footprint and producing the chemical building blocks needed for society. In this work, we performed a theoretical investigation of the differences and similarities of the CO2/CO catalytic reduction reactions in the gas, aqueous solution, and aprotic solution. We demonstrate that binding energy serves as a good descriptor for gaseous and aqueous phases and allows categorizing catalysts by reduction products. The CO vs. O and CO vs. H binding energies for these phases gives a convenient mapping of catalysts regarding their main product for the CO2/CO reduction reactions. However, for the aprotic phase, descriptors alone are insufficient for the mapping. We show that a microkinetic model (including the CO and H binding energies) allows spanning and interpreting the reaction space for the aprotic phase