Charge Accumulation and Polarization in Titanium Dioxide Electrodes

Abstract

Nanocrystalline TiO(2) electrodes were studied spectroelectrochemically by observing the simultaneous relaxation of the current and absorbance after applying a voltage step. The absorbance behaved differently in two time regimes: (1) ionic polarization in the oxide electrode, in which charged ions, such as Ti(3+) sites and/or interstitial Ti(4+) sites, move in response to the applied electric field, and (2) the diffusion of Li(+) ions into the TiO(2). These two behaviors were analyzed with equivalent circuit models. Li(+) ions reduce the resistance of the TiO(2) by approximately 90%, increase the capacitance by approximately 350%, and decrease the inductance by approximately 30%. Voltage cycling produces a buildup of intercalated Li(+) ions, lessening the electrode's response to the potential step, and causing it to become a more efficient inductor. The potential distribution in the nanoparticles is described by using a dielectric model in which roughly half the applied potential is dropped across the interface with a Li(+)-ion-containing electrolyte.

Engineering nanostructured electrodes and fabrication of film electrodes for efficient lithium ion intercalation

“…If the extra charge could not be readily transferred away after reaction, charge accumulation would occur to impede more reactions. 164,165 To ensure complete redox reactions, good charge transfer conductivity must be guaranteed; (2) during the longtime repeated intercalation/de-intercalation cycles, the electrode surface could possibly dissolve into the electrolyte and this problem was more severe for nanostructured electrodes because of the large solid/liquid interface. 166,167 The failure to maintain surface morphology integrity would directly lower intercalation capability, causing capacity degradation.…”

Exchange Process in the Dielectric Loss of Molecular and Macromolecular Ionic Conductors in the Interfacial Layers Formed by Electrode Polarization Effects

“…Ionic conductors − such as electrolytes, ionic liquids, polymer/ionic liquid blends, or poly­(ionic liquid)­s are materials of tremendous importance in many technological applications. − In contact with metal or carbon electrodes, these materials show a dramatic change in their mechanism of charge transport due to the phenomenon of electrode polarization. − This phenomenon, related to the formation of nanometric interfacial layers at the electrodes, has a large impact on the measured dielectric response of ionic conductors and leads to a tremendous increase in the effective values of the permittivity in the low frequency range. This has several important consequences.…”

GGA+Udescription of lithium intercalation into anataseTiO2

“…18,19 Nanocrystalline anatase TiO 2 also finds use in dye-sensitized solar cells ͑DSSC͒, where it acts as a transport medium for photogenerated electrons. Adding lithium to the electrolyte allows control of the electron injection yield from the dye to the TiO 2 electrodes [20][21][22][23] and the rate of interfacial charge recombination, 24 as well as increasing both the conductivity of the electrodes, 25 and resultant photovoltages. 26 Although surface polarization is likely to play a large role, 25 given the ease with which Li intercalates into anatase TiO 2 some interstitial Li is expected to be present.…”

“…Adding lithium to the electrolyte allows control of the electron injection yield from the dye to the TiO 2 electrodes [20][21][22][23] and the rate of interfacial charge recombination, 24 as well as increasing both the conductivity of the electrodes, 25 and resultant photovoltages. 26 Although surface polarization is likely to play a large role, 25 given the ease with which Li intercalates into anatase TiO 2 some interstitial Li is expected to be present. It has been suggested that interstitial lithium modifies the distribution of charge traps within the TiO 2 substrate, [26][27][28] with a consequential effect on the dynamics of charge carriers diffusing through the electrode.…”