Carbon paste electrodes of the mixed oxide SiO2/Nb2O5 prepared by the sol-gel method: dissolved dioxygen sensor

A carbon paste of SiO2/Nb2O5 material was used as the electrode in the development of a dissolved dioxygen sensor in 1.0 mol l−1 KCl solution at pH 6.2. The material was prepared by the sol-gel method. In the investigation of its electrochemical properties, linear and cyclic voltammetric and chronoamperometric techniques were employed. Dioxygen reduction, which was diffusion controlled, occurred at −280 mV vs. SCE by a two electron mechanism, producing peroxide. A linear response between the cathodic peak current intensity and the dissolved O2 concentration was obtained for the region between 1.0 and 13.6 mg l−1. The stability proved to be very good over successive voltammetric cycles. The electrode response time was about 5 s. The electron transfer reactions were explained as being to an n-type semiconductor of niobia dispersed in the silica surface.