Electrical and Physical Properties of Carbonized Charcoals

Because coal does not conduct electricity and graphite is costly and inert, little attention has been given to the development of a carbon fuel cell (i.e., a battery that utilizes a consumable carbon anode to generate electrical power). In this work we show that a packed bed of carbonized charcoal particles subject to a compressive pressure (ca. 8 MPa) can be a good electrical conductor (σ < 0.2 Ω·cm). Low electrical resistivities σ are manifest by many different charcoals after carbonization at a heat treatment temperature (HTT) of 950 °C. The 5 orders of magnitude decrease in the electrical resistivity of charcoal with increasing HTT from 650 to 1050 °C is not associated with any dramatic change in the carbons' X-ray diffraction spectrum, its Fourier transform infrared spectrum, or its elemental analysis. Our findings cause us to visualize carbonized charcoal to be a macromolecular, cross-linked, three-dimensional, aromatic structure replete with conjugation and π bonds that facilitate the movement of electrons, as well as nanopores, and micromolecular cracks. Because charcoal powder is competitive in price with fossil fuels and because carbonized charcoal is extremely reactive with a volumetric energy density (in a compacted packed bed) comparable to conventional liquid fuels, compact packed beds of carbonized charcoal hold promise for use as electrodes and consumable anodes in fuel cells. The packed-bed apparatus we describe is a prototype anode for use in a biocarbon fuel cell.