Design and Characterization\nof Metal Nanoparticle Infiltrated\nMesoporous Metal–Organic Frameworks

Abstract

The infiltration of palladium and\nplatinum nanoparticles (NPs)\ninto the mesoporous metal–organic framework (MOF) CYCU-3 through\nchemical vapor infiltration (CVI) and incipient wetness infiltration\n(IWI) processes was systematically explored as a means to design novel\nNP@MOF composite materials for potential hydrogen storage applications.\nWe employed a traditional CVI process and a new ″green″\nIWI process using methanol for precursor infiltration and reduction\nunder mild conditions. Transmission electron microscopy-based direct\nimaging techniques combined with synchrotron-based powder diffraction\n(SPD), energy-dispersive X-ray spectroscopy, and physisorption analysis\nreveal that the resulting NP@MOF composites combine key NP and MOF\nproperties. Room temperature hydrogen adsorption capacities of 0.95\nand 0.20 mmol/g at 1 bar and 2.9 and 1.8 mmol/g at 100 bar are found\nfor CVI and IWI samples, respectively. Hydrogen spillover and/or physisorption\nare proposed as the dominating adsorption mechanisms depending on\nthe NP infiltration method. Mechanistic insights were obtained through\nthe crystallographic means using SPD-based difference envelope density\nanalysis, providing previously underexplored details on NP@MOF preparations.\nConsequently, important host–guest correlations influencing\nthe global hydrogen adsorption properties are discussed, and they\ndemonstrate that employing MOFs as platforms for NPs is an alternative\napproach to the development of versatile materials for improving current\nhydrogen storage technologies.