Electrical conductivity of monolithic and powdered carbon aerogels and their composites

Kurzfassung

Carbon aerogels are three-dimensional, open-porous, amorphous materials introduced by R. Pekala 1989. Starting from organic aerogels, carbon aerogels exhibit unique properties such as well-controlled pore size distribution, high porosity, large specific surface area, high electrical conductivity, and low envelope density. This make them promising material for applications in adsorption, catalysis, supercapacitors or as a sulfur hosting material in cathodes of metal-sulfur battery cells. One of the key factors for electrochemical applications is the electrical conductivity. For amorphous carbon materials it is related to their electronic structure, the size of graphitic lattices or graphitic character, heteroatoms and so-called bulk electrical conductivity. In most electrochemical applications, the carbon materials are used as powders for e.g. electrode materials. Therefore, the measurement of the electrical conductivity of powder materials is of great importance. For powders, conductivity consists of: 1) the conductivity of individual grains and 2) the conductivity of the powder. The conductivity of individual grains depends only on monolithic conductivity of the material. In contrast, the conductivity of powder depends on several factors e.g. the shape of grains, their packing, compressibility, and the contact between the grains. Measurements of the electrical resistivity of powders are usually performed on the bed of grains under pressure. Within this presentation, we will report on our recent studies showing the correlation between structural, physical, mechanical and electrical properties of pure and activated carbon aerogels, as well as aerogel-composites. For this purpose, the influence of applied force, compressibility of aerogels and composites, and particle shape were investigated using the four-pin method to measure electrical conductivity. Monoliths and powders were measured at room temperature, and for powders the resistivity was determined in the force range from 1 to 20 kN. For structural and physical characterization nitrogen sorption, scanning electron microscopy, and pycnometry were used.