Li+ Ion Insertion in TiO2 (Anatase). 1. Chronoamperometry on CVD Films and Nanoporous Films

Electrochem. insertion of lithium in nanoporous and CVD samples of anatase was studied by chronoamperometry. The currents following cathodic and anodic potential steps were monitored as a function of film thickness, temp., and electrolyte concn. The time dependence of the currents generally exhibit the behavior of a diffusion-limited process. The magnitude of the currents scales directly with the inner area of the electrodes. The potential dependence on the rate of insertion and extn. indicates that the redn. of Ti4+ and oxidn. of Ti3+ is kinetically hindered. The double-layer capacitance and the adsorbate concn. at 0 V of the nanoporous structure are 30-40 μF/cm2 and 1.7-2.4 mol/cm2, resp. The chem. diffusion coeff. at 25° for insertion and extn. in the nanoporous structure was 1 × 10-17 and 4 × 10-17 cm2/s, resp. The corresponding values for the CVD samples, using the projected area, were 2 × 10-15 cm2/s for insertion and 6 × 10-15 cm2/s for extn. The activation energy for lithium insertion and extn. was 0.35 and 0.38 eV for the nanoporous films and 0.54 and 0.78 eV for the CVD samples.