Pore structure of hard carbon made from phenolic resin studied by ¹²⁹XeNMR

The pore structure of hard carbon samples made from two kinds of phenolic resins by heating between 1073 and 1473 K was investigated by ¹²⁹XeNMR. The difference of porous structure of hard carbon samples by heat treatment temperature, which was difficult to analyze precisely by general gas adsorption methods, could be evaluated by XeNMR at an equilibrium state of xenon gas adsorption. Carbon samples produced by heating precursors under a 0.1 MPa xenon atmosphere showed stronger NMR signals than carbon heated at reduced pressure, despite theiralmost identical powder X-ray diffraction (XRD) patterns. Applying this method, the dependence of NMR spectra on heating temperature between 1073 and 1473 K was examined. A carbon sample consisting of smaller particles showed almost constant shiftvalues at about 102 ppm, while the peak of another samplewith larger particles shifted between 118 and 82 ppm depending on the heating temperature. Then, almost all entrances of each sampleclosed above 1273 K. Using NMR with the improved heat- treatment by xenon gas, we evaluated pores in hard carbon that were hard to access from the outer surface of the hard carbon.