Electrical conductivity of ionic liquid electrolytes with alkali metal ions and the electrical double layer at MXene surfaces

CR Hua and Y Song and LH Lu and YJ Shi and SB Jiang, ELECTROCHIMICA ACTA, 542, 147533 (2025).

DOI: 10.1016/j.electacta.2025.147533

This work uses molecular dynamics (MD) simulations to study the conductivity characteristics of mixed electrolytes of alkali metal ions hexafluorophosphate (MPF6, M=Li, Na, K), 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6), and acetonitrile (ACN). Furthermore, the evolution of the electric double layer formed on Ti3C2Tx MXene surface with different surface terminations (--O and -OH) and their correlation with differential capacitance are investigated. It was found that the hybrid electrolyte of 1.2 M BMIMPF6-0.5 M MPF6ACN with ion pairing reaching equilibrium exhibited the highest conductivity, indicating that ion binding can effectively affect conductivity. The MXene surface terminations, alkali metal ion type, and the orientation of BMIM+ cations synergistically modulate the capacitance performance. Ti3C2(OH)2 surface induces vertical BMIM+ cation adsorption and has a high Li+ interfacial adsorption capacity, thereby achieving significant improvement in interfacial capacitance. The highest value of its differential capacitance reaches 62.04 mu F cm-2, which is higher than the capacitance value of general ionic liquid systems. This research displays the performance of the electric double-layer capacitance (EDLC) of ionic liquids (ILs) containing alkali metal ions on MXenes surface from a molecular level perspective, providing fundamental theoretical insights for the development of novel supercapacitors (SCs) with high energy and power density.

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