Unveiling electrical anisotropy of hierarchical pyrolytic biocarbons from wood cellulose

Hierarchical organization and structuring in multi-scale of natural materials and their derived products tune their mechanical behavior, chemical resistance, transport of fluids, heat and charges, among other characteristics explored for diverse human technological needs. Biocarbons obtained through pyrolysis of woody biomasses have found application in environmental and agricultural technologies, and more recently on electrical and electrochemical devices. By means of an integrated approach of advanced experimental and computational techniques, this work has stepped further on the fundamental knowledge to unveil the influence of wood cellulose hierarchical structuring on the structural, chemical, and electrical properties of the formed pyrolytic carbonaceous materials at multi-scale. It was not solely found that pyrolysis temperatures increase improves biocarbons graphitization degree and their electrical conductivity, but also that formed graphitic carbons have a preferential crystallographic orientation. The latter is induced by the pristine cellulose fibers organization in wood which resulted in electrical conductivity anisotropy up to three times. The formation of nanopores takes part at higher pyrolysis temperatures due to carbonaceous material backbone degradation preventing increase in the electrical conductivity by graphitization and diminishing the electrical conductivity anisotropy as electrons paths lengths get more similar.