Publications
Tunable thermodynamics and kinetics for hydrogen storage : nanoparticle synthesis using ordered polymertemplates
Theory and experiment suggest nanoscale hydride particles are destabilized relative to bulk, but the origin of this effect is unclear. Both size and local environment may play a role. The overall project objective is to achieve tunable thermodynamics for hydrogen storage materials by controlling nanoparticle size, composition, and environment. Key Goals for FY09 are: (1) Demonstrate and downselect infiltration methods; (2) Measure desorption kinetics for MgH{sub 2} and NaAlH{sub 4} nanoparticles and LiBH{sub 4} thin films; (3) Benchmark DFT and atomistic nanoparticle models using Quantum Monte Carlo (QMC); and (4) Quantify effect of nanoparticle size on {Delta}H{sub d}{sup o} using MgH{sub 2} as initial example. Summary of the key results are: (1) New highly ordered nanoporous templates enable systematic probing of nanoscale effects - Nanoscale NaAlH{sub 4} particles (as small as 1.5 nm diameter) exhibit improved H{sub 2} desorption kinetics relative to bulk and Preliminary data suggest MgH{sub 2} nanoparticle formation and possibly improved desorption kinetics; (2) Benchmarking DFT against QMC reveals significant errors that are non-systematic (H{sub 2} desorption energies underpredicted by as much as 30 kJ/mol); (3) QMC predicts greatest effect of size is for extremely small particles; e.g. (MgH{sub 2}){sub n}, n {le} 6 which is much smaller than predicted by Wolfe construction approach and observed in experiments and it suggests factors other than electronic structure (e.g. surrounding chemical environment) influence stability; (4) New NanoPEGS code developed and tested for MgH{sub 2} 2particles; and (5) New mass spec tool (STMBMS) reveals key details of hydrogen desorption process.