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A silica-cerium mixed oxide (SiCe) was prepared by the sol-gel process, using tetraethylorthosilicate and cerium nitrate as precursors and obtained as an amorphous solid possessing a specific surface area of 459 m(2) g(-1). Infrared spectroscopy of the SiCe material showed the formation of the Si-O-Ce linkage in the mixed oxide. Scanning electron microscopy/energy dispersive spectroscopy indicated that the cerium oxide particles were homogenously dispersed on the matrix surface. X-ray diffraction and (29)Si solid-state nuclear magnetic resonance implied non-crystalline silica matrices with chemical environments that are typical for silica-based mixed oxides. X-ray photoelectron spectroscopy showed that Ce was present in approximately equal amounts of both the 3+ and 4+ oxidation states. Cyclic voltammetry data of electrode prepared from the silica-cerium mixed oxide showed a peak for oxidation of Ce(3+)/Ce(4+) at 0.76 V and electrochemical impedance spectroscopy equivalent circuit indicated a porous structure with low charge transfer resistance. In the presence of nitrite, the SiCe electrode shows an anodic oxidation peak at 0.76 V with a linear response as the concentration of the analyte increases from 3×10(-5) at 3.9×10(-3) mol L(-1).

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This paper describes the construction and characterization of a biofuel cell with low-cost materials. The system uses the baker's yeast (Saccharomyces cerevisiae) as the microorganism responsible for the generation of voltage, whose interaction with the electrode is mediated by methylene blue. Simple experiments are proposed to evaluate the effects of different substrates, inhibitors and cell viability, improving both the knowledge of the system as well as metabolic pathway concepts to the student. The proposed device was able to generate a power density of 41 ± 0.3 mW m −2 , similar to those obtained with yeast-based biofuel cells. The low cost and easily acquisition of materials described allow the introduction of biofuel cell theme in different teaching levels, from high school to the college level.