Experimental and computational investigation of MOF-templated metal hydride nanoparticles

Recent theory and experiments suggest that reducing metal hydrides to the nanoscale enables hydrogen desorption thermodynamics and kinetics to be tuned, allowing bulk hydrides that are irreversible to be used for vehicular hydrogen storage. Metal-organic frameworks (MOFs) are excellent templates for nanoscale materials due to their ordered porosity and tailorable pore environments. We report infiltration of MOFs with metal hydrides and hydride precursors to create nanoclusters. Temperature-programmed desorption demonstrates accelerated H₂ desorption kinetics for NaAlH₄-infiltrated HKUST-1. We also benchmarked desorption energies of (MgH₂)_n nanoclusters predicted by ab-initio density functional theory (DFT) against highly accurate quantum Monte Carlo (QMC) calculations. The error of standard DFT (GGA-PBE) relative to QMC increases with cluster size, from 2-3 kJ/mol for very small clusters (n=3) to >20 kJ/mol for large clusters (n=40). Our results demonstrate the critical need of highly accurate methods, such as QMC, for obtaining quantitatively reliable predictions of metal-hydride reaction energetics.