ILs generally have high ionic concentrations, wide ranges of electrochemical stability, and moderate conductivity which combine to make them promising electrolytes, solvents, and energy storage media via electrochemical double-layer capacitors. The imidazolium class of RTILs displays prominent capacitive features in AC voltammetry and single frequency impedance measurements, which indicate major molecular reorientations within the IL/electrode ‘double-layer’ region. Our data correlate these capacitive features with surface sensitive vibrational spectroscopies (sum frequency generation and infrared reflection absorption) on metallic electrodes to create spectro-electrochemical data sets. Special attention is given to large capacitive hysteresis effects observed with respect to the direction of applied electrochemical potential and the slow response of molecular-ion ordering with respect to the applied electrochemical potential. We specifically investigate the effects of reducing the bulk viscosity on the capacitance by diluting the ILs with molecular organic solvents, i.e. acetonitrile. Viscosity ranges more than three orders of magnitude (350 cP for pure IL, to 0.36 cP for pure acetonitrile) which significantly affects the rates at which the electrode voltage approaches the open circuit potential (OCP) after an applied potential over a ca. 4 V window. The spectroscopic probes provide insight into the molecular scale organization over this time, as the electrode voltage is held, swept, or allowed to return to OCP. Results via electrochemical measurements and vibrational spectra show how changes in viscosity, affect the reorganization time in response to an applied potential.<br/>

Viscosity dependent dynamics of electrochemically driven molecular reorientations revealed via vibrational spectro-electrochemistry

255th National Meeting (2018)

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