Abstract
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.
| Original language | English |
|---|---|
| Pages (from-to) | 4953-4964 |
| Number of pages | 12 |
| Journal | Carbon |
| Volume | 50 |
| Issue number | 13 |
| DOIs | |
| State | Published - Nov 2012 |
Funding
Work at NIST was partially supported by the Office of Energy Efficiency and Renewable Energy (EERE) through the Hydrogen Sorption Center of Excellence. Synthesis science on carbon nanostructure growth was funded by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences at DOE. Characterization of SWCNHs was funded by EERE Center of Excellence on Hydrogen Sorption Center of Excellence and independent research at the Center for Nanophase Materials Sciences and SHaRE User Facility, Division of Scientific User Facilities, DOE-BES. Oak Ridge National Laboratory is operated under the management of UT-Battelle, L.L.C. for the US Department of Energy under Contract No. DE-AC05-00OR22725.