The ortho-para transition, confinement and self-diffusion of H₂ in three distinct carbide-derived carbons by quasi- and inelastic neutron scattering

¹ Institute of Chemistry, University of Tartu, Ravila 14a, 50411 Tartu, Estonia
² Department of Applied Physics, KTH Royal Institute of Technology, SE-106 91 Stockholm, Sweden
³ Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin, Germany
⁴ Department of Geology, University of Tartu, Ravila 14a, 50411 Tartu, Estonia
⁵ Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, Forschungsstrasse 111, CH-5232, Villigen PSI, Switzerland

^* Corresponding author: riinu.harmas@ut.ee

Published online: 9 October 2023

Abstract

Microporous carbon materials are promising for hydrogen storage due to their structural variety, high specific surface area, large pore volume and relatively low cost. Carbide-derived carbons are highly valued as model materials because their porous structure is fine-tuned through the choice of the precursor carbide and the synthesis route. This study investigates H₂ adsorption in three carbide derived carbons with well-defined pores and pore size distributions with quasi- and inelastic neutron scattering methods. Concerning previous studies, a wider neutron energy transfer window is investigated, and a detailed quantitative evaluation of the graphitic structure is presented. The graphitic structure of the carbon is shown to influence the speed of the ortho-to-para transition of H₂. Namely, the ortho-para transition was the slowest in carbon derived from TiC, which also had the smallest average stacking size of graphene layers. The possibility to inhibit the ortho-para transition in cryo-adsorption devices is sought after to mitigate the evaporation of H₂ during storage. In addition, the self-diffusion of H₂ in different timescales is detected in carbon derived from Mo₂C, demonstrating the usefulness of obtaining data in a wide energy window.