Hydrogen densification in carbon nanopore confinement: Insights from small-angle neutron scattering using a hierarchical contrast model

• Published in: Carbon (New York) 2024-03, Vol.221, p.118911, Article 118911
• Main Authors: Stock, Sebastian, Seyffertitz, Malina, Kostoglou, Nikolaos, Rauscher, Max Valentin, Presser, Volker, Demé, Bruno, Cristiglio, Viviana, Kratzer, Markus, Rols, Stéphane, Mitterer, Christian, Paris, Oskar
• Format: Article
• Language: English
• Subjects: Activated carbon cloth; Hierarchical pore model; Hydrogen physisorption; Nanoporous carbon; Small-angle neutron scattering
• ISSN: 0008-6223; 1873-3891
• DOI: 10.1016/j.carbon.2024.118911

This study reports on the low-pressure hydrogen (H2) and deuterium (D2) physisorption processes in nanoporous activated carbon cloth at supercritical temperatures. In-situ small-angle neutron scattering (SANS) is employed as a hydrogen-sensitive method to determine the pore-size-dependent and isotope-dependent adsorbate densification for different gas pressures up to 1 bar. The changes of the SANS signal resulting from the physisorption of adsorbate molecules in the pore space is described by analytical pore scattering functions resembling slit-like pores. Analysis based on a hierarchical pore model allows quantifying the pore-size-dependent physical density of the confined adsorbate for three pore classes, resembling roughly the IUPAC classes of ultramicropores, supermicropores, and mesopores. While the adsorbate density within the very smallest pores approaches the bulk solid density of H2 for pressures of about 1 bar at 77 K, it remains much lower for larger pores. A high density is also found for D2 within ultramicropores, but these results are hampered by a subtle effect of an exchange of chemically bound hydrogen by deuterium in the sample. These findings contribute to a fundamentally better understanding of confinement effects on hydrogen densification, and affect materials design for efficient hydrogen storage devices working at realistic cryogenic conditions and low pressures. [Display omitted] •Quantification of density evolution of H2 and D2 adsorbed in nanoporous activated carbon cloth at supercritical temperatures.•Hierarchical model of slit-like pores for SANS data reveals pore-size-dependent adsorbate densification.•Adsorbate density in pores smaller than 0,7 nm approaches bulk solid density at 77 K and ambient pressure.