Hydrogen diffusion in potassium intercalated graphite studied by quasielastic neutron scattering

Area of Science:

• Materials Science
• Physical Chemistry
• Condensed Matter Physics

Background:

• Graphite intercalation compounds like KC24 can adsorb hydrogen.
• Hydrogen adsorption in KC24 forms a 2D condensed phase.
• Strong adsorption potentials and steric barriers are predicted to limit hydrogen diffusion in KC24.

Purpose of the Study:

• To experimentally measure and simulate hydrogen self-diffusion in KC24.
• To compare experimental diffusion data with molecular dynamics simulations.
• To understand hydrogen mobility within the KC24 host structure.

Main Methods:

• Quasielastic neutron scattering (QENS) was used to measure H2 self-diffusion.
• Molecular dynamics (MD) simulations were performed for comparison.
• Experimental spectra were fitted to a honeycomb net diffusion model.

Main Results:

• Experimental H2 diffusion coefficients in KC24 were determined.
• Values ranged from 3.6 x 10^-9 m^2/s at 80 K to 8.5 x 10^-9 m^2/s at 110 K.
• Experimental and simulated diffusion coefficients showed good agreement.

Conclusions:

• Hydrogen diffusion in KC24 is significantly slower than in carbon adsorbents.
• The measured diffusion rates are comparable to those in molecular sieve zeolites.
• The honeycomb net diffusion model accurately describes H2 mobility in KC24.