ELECTRICAL-PROPERTIES OF CARBONS - RESISTANCE OF POWDER MATERIALS

The authors studied a large number of Brazilian carbonaceous materials, having in view the construction of gas diffusion electrodes for fuel cells. An apparatus was designed, with the same idea of a sample cell under pressure as one by L. R. Brodd and A. Kosawa in 1978; the fundamental modifications introduced resulted in considerable improvement in precision. A detailed design of the apparatus and the electrical circuit used are presented. It is evident from the curves that carbons are ohmic resistors and that a strong dependence exists between resistivity and pressure, such that only at fixed and constant pressures a comparison of the resistivity values is meaningful. Gas diffusion electrodes were manufactured with a composite prepared from a paste of the carbonaceous material. An electrographite, a petroleum coke and an acetylene black exhibited excellent electrical properties as electrode materials.