title: 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.
authors.affiliation: Department of Physics, Imperial College, Blackett Laboratory, Prince Consort Road, London SW7 2BZ, United Kingdom. carol.olson@fotomol.uu.se
authors.forename: Carol L
authors.initials: CL
authors.lastname: Olson
authors.forename: Ian
authors.initials: I
authors.lastname: Ballard