Positron annihilation lifetime spectroscopy for ultramicroporosimetry of porous carbons

Positron annihilation lifetime spectroscopy (PALS) has been used to analyse ultramicropore structures in silica-based porous materials. Energy-related applications increasingly demand improved characterisation of ultramicropore structures in carbon materials. However, PALS porosimetry has not been well established for porous carbons. Therefore, this study aimed to apply the PALS-aided ultramicroporosimetry to carbon materials. We employed single-walled carbon nanotube (SWCNT) bundles with tube diameters of 1.5 and 2.0 nm to determine the key parameter δ which reflects the collision between positronium and the carbon electron clouds and is an essential factor for analysing PALS data related to carbon materials. The SWCNT bundles featured two types of pores—internal tube spaces and interstitial subnanoscale spaces—which were characterised using X-ray diffraction. PALS measurements of these SWCNT samples yielded the parameter δ for carbon materials. The obtained δ was 0.23 nm. Using this value, we performed PALS analysis of reduced graphene oxide, which revealed the presence of pores approximately 0.13 nm wide. These pores are attributed to the staggered structure of GO prior to thermal reduction.