Metal-assisted hydrogen storage on Pt-decorated single-walled carbon nanohorns

The catalytic dissociation of hydrogen molecules by metal nanoparticles and spillover of atomic hydrogen onto various supports is a well-established phenomenon in catalysis. However, the mechanisms by which metal catalyst nanoparticles can assist in enhanced hydrogen storage on high-surface area supports are still under debate. Experimental measurements of metal-assisted hydrogen storage have been hampered by inaccurate estimation of atomically stored hydrogen deduced from comparative measurements between metal-decorated and undecorated samples. Here we report a temperature cycling technique combined with inelastic neutron scattering (INS) measurements of quantum rotational transitions of molecular H ₂ to more accurately quantify adsorbed hydrogen aided by catalytic particles using single samples. Temperature cycling measurements on single-wall carbon nanohorns (SWCNHs) decorated with 2-3 nm Pt nanoparticles showed 0.17% mass fraction of metal-assisted hydrogen storage (at ≈0.5 MPa) at room temperature. Temperature cycling of Pt-decorated SWCNHs using a Sievert's apparatus also indicated metal-assisted hydrogen adsorption of ≈0.08% mass fraction at 5 MPa at room temperature. No additional metal-assisted hydrogen storage was observed in SWCNH samples without Pt nanoparticles cycled to room temperature. The possible formation of C-H bonds due to spilled-over atomic hydrogen was also investigated using both INS and density functional theory calculations.