Femtosecond Electron Solvation at the Ionic Liquid/Metal Electrode Interface

Abstract

Electron solvation is examined at the interface of a room temperature ionic liquid (RTIL) and an Ag(111) electrode. Femtosecond two-photon photoemission spectroscopy is used to inject an electron into an ultrathin film of RTIL 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([Bmpyr](+)[NTf2](-)). While much of current literature highlights slower nanosecond solvation mechanisms in bulk ionic liquids, we observe only a femtosecond response, supporting morphology dependent and interface specific electron solvation mechanisms. The injected excess electron is found to reside in an electron affinity level residing near the metal surface. Population of this state decays back to the metal with a time constant of 400 ± 150 fs. Electron solvation is measured as a dynamic decrease in the energy with a time constant of 350 ± 150 fs. We observe two distinct temperature regimes, with a critical temperature near 250 K. The low temperature regime is characterized by a higher work function of 4.41 eV, while the high temperature regime is characterized by a lower work function of 4.19 eV. The total reorganizational energy of solvation changes above and below the critical temperature. In the high temperature regime, the electron affinity level solvates by 540 meV at 350 K, and below the critical temperature, solvation decreases to 200 meV at 130 K. This study will provide valuable insight to interface specific solvation of room temperature ionic liquids.

From two-dimensional electron gas to localized charge: Dynamics of polaron formation in organic semiconductors

“…Such an evolution from dispersive to nondispersive behavior cannot be observed in IPS on metal surfaces [11] and is related to the molecules. The observation can be explained by electron localization [12][13][14][15][16][17][18]26]. Similar temporal change in the band structure is found for the 1 ML sample.…”

“…Similar to charges in adsorbate's unoccupied states, electrons in IPS are subject to electron-vibrational interactions and the dielectric environment originated from the adsorbates. These interactions can lead to dynamic localization of the IPS, which has been studied by TR-ARPES in systems such as alkanes and polar solvents on metal surfaces [13][14][15][16], ionic liquids [17], and ionic crystals [18]. Recently, TR-ARPES has been used to study 2-D states at organic/metal interfaces [19][20][21] and organic semiconductor surfaces [22][23][24][25].…”

Viscosity, Conductivity, and Electrochemical Property of Dicyanamide Ionic Liquids

“…In comparison with traditional molecular solvents, ILs have many unique physical properties such as negligible vapor pressure, large liquidus range, high thermal stability, and wide electrochemical window (Galinski et al, 2006 ; Andriyko et al, 2009 ). Functionalized ILs/task-specific ILs have already become general pattern to prepare new ionic liquid materials based on the remarkable “design” capacity of ILs (Muller et al, 2013 ). The design processes of novel materials sorely depend on empirical rules.…”

Electrode–Electrolyte Interfacial Processes in Ionic Liquids and Sensor Applications

“…Our studies and others have shown that the capacitance of IL/electrode interface is potential dependent, and the adsorption of gas on the IL/electrode interface will decrease the double-layer capacitance under a specific DC bias potential [80]. In contrast to the EDL typically observed in dilute aqueous or nonaqueous electrolytes, the ions of ILs are strongly oriented near the electrode into an ordered layer structure with local ion density at maximum possible value [81,82]. Multiple ion pair layers form at the interface of IL and metal electrode.…”