Transport properties of H 2 confined in carbide-derived carbons with different pore shapes and sizes Riinu H € armas a , Rasmus Palm a, * , Margarita Russina b, ** , Heisi Kurig a , Veronika Grzimek b , Eneli H € ark b , Miriam Koppel a , Indrek Tallo a , Maarja Paalo a , Ove Oll a , Jan Embs c , Enn Lust a a Institute of Chemistry, University of Tartu, Ravila 14a, 50411, Tartu, Estonia b Helmholtz Zentrum Berlin, Hahn-Meitner-Platz 1,14109, Berlin, Germany c Paul Scherrer Institute, Forschungsstrasse 111, 5232, Villigen, Switzerland article info Article history: Received 18 June 2019 Received in revised form 7 August 2019 Accepted 11 August 2019 Available online 19 August 2019 abstract Hydrogen adsorption in highly porous carbon with well-defined pores, with three different shapes, and different sizes ranging from sub-to nanometers is investigated. Using a combined approach of volumetric gas adsorption method and in-situ quasi-elastic neutron scattering method the relationship between final macroscopic intake properties, details of the local adsorbent structure and the molecular behaviour of confined hydrogen are established. It is shown that sub-nanometer pores of spherical and cylindrical shape strongly limit the diffusion of H 2 , and thus, enhance the H 2 storage capability of carbons with well- tailored pore structure. In mesoporous carbide-derived carbon, the formation of a hydrogen layer with reduced mobility close to the pore walls is observed. With the increase in the amount of confined hydrogen and the occupation of the centre pore area, the mobility of confined hydrogen increases in a jumpelike fashion. Surprisingly, the increase of hydrogen diffusion is also observed at higher hydrogen loadings, indicating that cooperative H 2 eH 2 interactions might play a role. © 2019 Elsevier Ltd. All rights reserved. 1. Introduction The structural variety, high specific surface area, large pore volume and relatively low cost make microporous carbons a promising candidate as adsorbents for hydrogen storage [1] or hydrogen adsorptive applications such as isotope separation [2] or catalysis [3,4]. The strong influence of the specific surface area and micropore volume in combination with subnanometer pores to- wards the adsorption of high quantities of hydrogen at lower pressures and higher temperatures has been reported [1 ,5e9]. However, since these materials are often strongly disordered and with a broad distribution of pore sizes and geometries, they are tedious to model, which creates difficulties in understanding the connection between the local structure and the final intake parameters. In this study four carbide-derived carbons (CDCs); CeTiC 950, CeSiC 1000, CeMo 2 C 900, and CeMo 2 C 1000 have been chosen based on the well-defined pore size distributions and their high capability to adsorb hydrogen. The pore size distributions from sub- nanometer to nanometer size have been determined by simulta- neous modelling of N 2 and CO 2 adsorption data with two- dimensional non-local density functional theory for carbons with heterogeneous surfaces (2D-NLDFT-HS) model [10]. Furthermore, the most prevalent pore shape has been determined by Kurig et al. for CeTiC 950, CeSiC 1000 and CeMo 2 C 1000 using D 2 O contrast matching small-angle neutron scattering [11] at V16 station at Helmholtz Zentrum Berlin [12]. As the prevalent pore shape differs between materials, e.g. spherical (CeSiC 1000), cylindrical (CeTiC 950), and slit-like (CeMo 2 C 1000), these materials present an excellent opportunity to investigate the confinement of H 2 inside different shaped pores and yield a better understanding of the in- teractions between H 2 and differently structured adsorbents. Since sorption processes are diffusion-based phenomena we have used a combination of the gas adsorption isotherm mea- surements, to establish the macroscopic intake behaviour, and in- situ quasi-elastic neutron scattering (QENS) techniques. QENS, in * Corresponding author. ** Corresponding author. E-mail addresses: rasmus.palm@ut.ee (R. Palm), margarita.russina@helmholtz- berlin.de (M. Russina). Contents lists available at ScienceDirect Carbon journal homepage: www.elsevier.com/locate/carbon https://doi.org/10.1016/j.carbon.2019.08.041 0008-6223/© 2019 Elsevier Ltd. All rights reserved. Carbon 155 (2019) 122e128