Low-temperature sol–gel nanocrystalline tin oxide: Integrated characterization of electrodes and particles obtained by a common path

Nanocrystalline, nanostructured, defective tin oxide particles and electrodes (supported on Ti) were prepared by a common synthetic path. The electrodes were characterized by cyclic voltammetry and impedance spectroscopy in a potential range, purportedly selected to exclude the hydrogen and oxygen evolution reactions as well as any other faradaic reaction involving the massive reduction of SnO2. Parallel particle characterization was performed by BET and electrophoretic mobility. A synergistic enhancement of the descriptive capability of each investigation technique is obtained. In particular, the semiconducting properties of the Ti/SnO2 electrodes are obtained and discussed in term of emptying/filling of the electronic traps within the band gap that is in terms of oxide resistance and electron trapping capacitance. In addition the voltammetric total, outer and inner charge quantities, Qtot, Qout and Qin, are determined and interpreted in terms of “electrochemical” porosity of the oxide layer. The outcomes are in total agreement with the BET investigations of the powder. The electric surface characteristics are parallelly investigated by the pH dependence of the oxide/solution capacitance of the electrodes and by the electrophoretic mobility of the particles. The results jointly point to a substantial reduction of charge accumulation capability at pH > 5–6, where a net negative charge is observed on the surface.