In-depth fine structure of carbon micropores with positron annihilation lifetime spectroscopy

The detailed pore structure analysis of nanoporous carbons is essential for designing high-performance materials for clean-energy technologies. We used activated carbon fibres (ACFs) with average pore sizes of 0.8 and 1.3 nm. Using an ACF-polytetrafluoroethylene sample, the carbon-specific positron annihilation lifetime (CS-PAL) of the ACF was determined based on the lifetime versus ACF content relationship. Pore sizes determined by CS-PAL spectroscopy were smaller than those reported by Ar adsorption: ACFs of 0.8 and 1.3 nm were 0.4 and 0.2 nm, respectively, suggesting that the 0.8 nm-ACF exhibited single-layered graphitic islands within the pore and the 1.3 nm-ACF had plain pore walls. • Nanoporous carbon is vital to clean energy materials. • Pore structure analysis with argon adsorption is difficult to measure small ultramicropores. • Carbon-specific positron annihilation lifetime spectroscopy for carbon ultramicropores. • PALS data revealed fine structures within pores inaccessible to other methods. • Carbon-specific positron annihilation lifetime spectroscopy can permit rational design of nanoporous materials.