Precise functionalization of electrodes with size-selected ionic liquid (IL) clusters may improve the application of ILs in electrochemical separations. Herein, we report our combined experimental and theoretical investigation of the IL clusters [EMIM]????[BF4]????+1- (n = 1 – 9) and demonstrate their selectivity and efficiency towards targeted adsorption of molecules from solution. The structures and energies of the IL clusters, predicted with global optimization, agree with and help interpret the ion abundances and stabilities measured by high mass resolution electrospray ionization mass spectrometry and collision induced dissociation experiments. The [EMIM][BF4]2- cluster, which was identified as the most stable IL cluster, was selectively soft landed onto a working electrode. Electrochemical impedance spectroscopy revealed a lower charge transfer resistance on the soft-landed electrode containing [EMIM] [BF_4 ]_2^- compared to an electrode prepared by drop casting of IL solution, which contains the full range of IL clusters. Our findings indicate that specific IL clusters may be used to increase the efficiency of electrochemical separations by lowering the overpotentials involved.
Revised: February 12, 2021 |
Published: August 20, 2020
Citation
Zhang J., E.T. Baxter, M. Nguyen, V. Prabhakaran, R.J. Rousseau, G.E. Johnson, and V. Glezakou. 2020.Structure and Stability of the Ionic Liquid Clusters [EMIM]n[BF4]n+1- (n = 1 – 9): Implications for Electrochemical Separations.The Journal of Physical Chemistry Letters 11, no. 16:6844-6981.PNNL-SA-153510.doi:10.1021/acs.jpclett.0c01671