Localized crystallization of polyfurfuryl alcohol derived carbon by alkali metals Original Research Article

The interaction of alkali metals with polyfurfuryl alcohol (PFA) derived nanoporous carbon (PFA-NPC) leads to localized regions of crystallization within the carbon. This is interesting because PFA-derived carbon is well known to be non-graphitizing, meaning that it does not tend to crystallize even at very high temperature (>2500 °C). However, it has been demonstrated that after an oxidation with carbon dioxide, the PFA-NPC will crystallize at lower temperatures. Here, we show that localized crystallization of non-crystalline carbon takes place in the presence of each of the alkali metals, except lithium, under apparently mild conditions. At the local level, as adduced by HRTEM and electron diffraction analyses, cesium showed the greatest extent of ordering when compared to other alkali metals. However, when the materials are probed with bulk analyses, (X-ray diffraction, Raman spectroscopy, and NEXAFS), we do not observe evidence of gross crystallization. Therefore, it is our conclusion that local ordering occurs upon exposure of the alkali-containing PFA-NPC samples to air and that it occurs at the edges of the carbon particles. The ordering takes place as the alkali metals combust. We also conclude that carbons do not combust because the rate of oxygen transport into the sample is slowed by resistance in the nanopores as well as the resistance induced by the temperature gradient at the near surface region. Both phenomena prevent the gross combustion of the particle.