Manipulation of the crystalline phase diagram of hydrogen through nanoscale confinement effects in porous carbons

Abstract

Confinement of H2 in subnanometre pores of microporous carbon stabilizes the lowest energy crystal confirmation at higher temperatures. Change in H2 phase behaviour shown to be caused by severe loss of rotational freedom and energy upon confinement.

Supported Metal Nanoparticles‐Based Catalysts and their Interactions with H2: Insights from Inelastic Neutron Scattering Spectroscopy

“…The fact that this signal, typical for solid para‐H 2 , is observed at a temperature above the H 2 triple point has been one of the indicators that H 2 can form a solid‐like phase when trapped inside pores of a few nanometers of diameter [6,8a,39a,b,43] . The other two peaks observed at 107 and 132 cm −1 , instead, were attributed to H 2 molecules trapped inside sub‐nanometric slit pores and experiencing a strong anisotropic potential [6,8a,39a,b,43] . Under these conditions the degeneracy between the (J=1, M J =0) and (J=1, M J =±1) rotational energy levels is lost, resulting in a split of the signal.…”

“…The central peak, centered at about 120 cm −1 , is attributed to H 2 weakly adsorbed within the micropores of the carbon. The fact that this signal, typical for solid para‐H 2 , is observed at a temperature above the H 2 triple point has been one of the indicators that H 2 can form a solid‐like phase when trapped inside pores of a few nanometers of diameter [6,8a,39a,b,43] . The other two peaks observed at 107 and 132 cm −1 , instead, were attributed to H 2 molecules trapped inside sub‐nanometric slit pores and experiencing a strong anisotropic potential [6,8a,39a,b,43] .…”

Hydrogen sorption on microporous carbon/sulfur nanocomposite systems

“…In comparison, w-SWCNT-777 falls short of Chahine's rule and only adsorbs 1.67AE 0.02 wt% of H 2 . This may be attributed to the more significant proportion of ultramicropores around the claimed optimum pore size of approximately 0.7 nm in the w-SWCNT-121 and w-TE7 (see Table 2), where increased overlap of electrostatic potentials from opposing walls generates stronger binding sites, 5,25 thus, providing more desirable adsorption sites and allowing for more significant H 2 densification. Following sulfur encapsulation, both S@SWCNT-121 and S@TE7 show a reduction in maximum excess H 2 sorption by 32% and 50%, at 77 K, respectively.…”

“…[19][20][21] Improving the CNT-H 2 interaction strength through modifying the composition of the material may provide a route to overcoming Chahine's Rule whilst maintaining several of the other desirable properties of CNTs. 12,[22][23][24][25] Modifications to the adsorbent surface through doping or functionalisation may alter the adsorbate-adsorbent interactions through modulating the electronic structure of the surface, 26 thus changing the Lennard-Jones interactions between the incoming adsorbate molecules and solid adsorbent. 27 Tailoring these interactions may be achieved by adding heteroatoms into the porous structure, replacing specific units of the chemical structure, or adding functional groups such as amines to the surface.…”

“…19–21 Improving the CNT–H 2 interaction strength through modifying the composition of the material may provide a route to overcoming Chahine's Rule whilst maintaining several of the other desirable properties of CNTs. 12,22–25…”