Inter-particle charge transfer in TiO2-phytate films: Generator–collector gold–gold junction transients

Self-assembled films of nanoparticulate TiO2-phytate are prepared on a gold disc–gold disc junction electrode with approximately 6 μm inter-electrode gap. Charge diffusion dominated by inter-particle hopping of electrons is investigated (in contrast to bulk charge transport) for films immersed in 0.1 M phosphate buffer solution at pH 7 using gold–gold generator–collector voltammetry and chronoamperometry techniques. Numerical simulation based on a basic “randomly propagating” finite difference approach is employed to reveal first approximation potential-dependent apparent diffusion coefficients and apparent concentrations for electrons (Dapp increases from 9 × 10−11 to 18 × 10−11 m2 s−1 and capp increases from 0.2 to 37 M when going from −0.8 to −1.2 V vs. SCE). A mechanistic model for inter-particle versus intra-particle electron hopping is developed. Applications of the inter-particle charge hopping process in electrochemical sensing are suggested.