Ultrahigh-temperature conversion of biomass to highly conductive graphitic carbon

Graphitic carbon has attracted tremendous research interest in recent years owing to its exceptional thermal and electrical properties that arise from the ordered sp2 hybridized carbon structure. Due to its high activation energy, graphitization is often energy- and chemical-intensive. In addition, the electrical conductivity of graphitized materials has always been limited by the presence of intrinsic defects. In this paper, we propose a new method to convert lignin-based biomass into highly crystalline graphitic carbon by a Joule heating process. The Joule heating utilizes the internal resistance of a reduced graphene oxide/lignin (rGO-lignin) carbon film to heat the sample to up to 2500 K within 1 h. The annealing of lignin at this high temperature is found to remove impurities and intrinsic defects, as well as to initiate the graphitization process. Amorphous lignin carbon can be converted into short-range ordered and graphitic carbon with an ultrahigh electrical conductivity of 4500 S/cm, significantly higher than the original 6.4 S/cm. The microstructure change underlying this high electrical conductivity was further probed through electron microscopy and chemical analysis. This highly crystalline, electrically conductive graphitized lignin-carbon is expected to be useful for numerous applications where high conductivity and corrosion resistance are desired.