Tracking micropore evolution during the carbonization of macroporous resorcinol–formaldehyde gels

Resorcinol-Formaldehyde (RF) gels exhibit a dynamic variation of micropore properties upon carbonization, which is correlated with the structural reorganization from a crosslinked polymer network to amorphous carbon matrix. Understanding the micropore evolution during the carbonization of RF gels in association with the underlying mechanism is conducive to the control of pore properties for RF-derived carbon materials utilized for various applications, such as Na-ion battery anodes. In this study, the thermogravimetric technique combined with evolved gas analysis and the gas sorption measurements using N2 and CO2 have been employed to investigate the pyrolysis and carbonization behavior of the macroporous RF monolith prepared by the sol–gel process accompanied by phase separation. It is proposed that the micropore evolution commences at ~400 °C in the second pyrolytic step and continues up to ~900 °C at the end of the third pyrolytic stage. Micropores in the RF-derived carbon gradually decrease at elevated temperatures up to ~1400 °C. The drastic reduction of micropores takes place between 1400 °C and 1600 °C probably due to the narrowing of micropore windows, rendering the micropores “closed” to N2 and CO2 molecules.