Neutron Scattering of Hydrogen Confined in Nanoporous Carbons for Sustainable Aviation

As the aerospace sector seeks an ambitious transition to Net Zero by 2050, liquid hydrogen (LH2) will play a pivotal role in decarbonising aviation. Researchers at the universities of Bath, Bristol and Exeter, in collaboration with neutron scattering experts at ISIS, is exploring how solid-state hydrogen storage, particularly physisorption in nanoporous materials, can unlock the technologies needed to enable truly sustainable flight. By the design or selection of pore size and geometry, it may be possible to optimise adsorbents towards passive and high-density storage under favourable conditions for applications such as sensing and leak prevention or the mopping of fugitive gases. Neutron scattering experiments and high-pressure sorption modelling reveal how confined hydrogen remains stable above the critical temperature (33 K), supporting the next-generation of safe and secure LH₂ infrastructure for aerospace and beyond.
Single-walled carbon nanotubes (SWCNTs), with rigid, monodisperse structures and a lack of heteroatoms, present an ideal model material for studying physical confinement effects. Through a combination of inelastic (TOSCA) and quasi-elastic (IRIS) neutron scattering techniques, the phase and self-diffusional dynamics of hydrogen molecules can be explored in detail. Modelling of high-pressure sorption isotherms at multiple temperatures reveals solid-like hydrogen adsorbates with remarkable densities, greater than that of LH2 (~71 kg m–3). Whilst well established that nanopores, approximately 0.7 nm in diameter, create traps leading to these exceptional densities, this work directly examines how pore structure leads to the persistence of these states at elevated temperatures or lower pressures. Analysis of the neutron spectra indicates that sub-nanometre pores are critical for confinement in these conditions, but that geometry also significantly affects hydrogen dynamics and may lead to steric traps. Accurate characterisation of these phenomena will inform the creation of efficient sensor and leak prevention platforms, important for the safe and effective management of LH2 within aircraft.