Electrical conductivity of monolithic and powdered carbon aerogels and their composites

Kurzfassung

Carbon aerogels are three-dimensional, open-porous, amorphous materials produced via carbonization of organic aerogels such as resorcinol-formaldehyde, phenol-formaldehyde, resorcinol-formaldehyde-melamine, or biomass-based ones. Unique properties of carbon aerogels such as well-controlled porosity, large specific surface area, high electrical conductivity, and low envelope density make them promising material for applications in adsorption, catalysis, supercapacitors or as a cathode host in lithium-sulfur battery cells. Their electrical conductivity, remarkable for porous materials, is one of the key factors for electrochemical applications. The electrical conductivity of amorphous carbon materials 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 aerogels 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 conductivity of the material (monolithic conductivity). 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 the presentation, we will report on our studies showing the correlation between structural, physical, mechanical and electrical properties of pure and activated carbon aerogels, as well as aerogel-composites. Furthermore, the influence of applied force, compressibility of aerogels and composites, and particle shape were investigated by using the four-pins-method. The conductivity of monoliths and powders was measured at room temperature, for powders the resistivity was determined in the force range from 0.1 to 20.0 kN. For structural and physical characterization Raman spectroscopy, nitrogen sorption, scanning electron microscopy, and pycnometry were used.