Nanoporous Pd Alloys with Compositionally Tunable Hydrogen Storage Properties Prepared by Nanoparticle Consolidation

Cappillino, P.J., J.D. Sugar, M.A. Hekmaty, B.W. Jacobs, V. Stavila, P.G. Kotula, D.B. Robinson, et al., 2012

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Abstract

Nanoporous palladium and palladium alloys are expected to have improved mass transport rates and cycle life compared to bulk materials for energy storage and other applications due to high ratios of surface area to metal volume. Preparation of such materials with high thermal stability and well-controlled metal composition, however, remains a challenge. This work describes a scalable, bottom-up technique for preparing nanoporous palladium alloys based on partial consolidation of dendrimer-encapsulated nanoparticles (DEN). Destabilization of a colloidal suspension of DEN and purification yields high surface area material (60–80 m2 g−1) with a broad pore size distribution centered between 20 and 50 nm. This approach allows for precise tuning of product composition through adjustment of the composition of the precursor DEN. Nanoporous Pd0.9Rh0.1 alloys with uniform composition or with Rh enrichment at pore walls and grain boundaries have been prepared and these structures have been confirmed with high-spatial resolution, aberration corrected quantitative STEM-EDS. Compared to bulk alloys of the same nominal composition, the nanoporous bimetallics show much faster hydrogen uptake kinetics, and store hydrogen at much lower pressure. Pore structure remains intact to temperatures above 300 °C, suggesting that these materials will have long lifetimes at the temperatures used for hydrogen storage applications.

Impact Statement

Heated nanoporous Pd/Rh alloy particles synthesized via a two-step method. Initially nanoparticles were formed within dendrimers. The dendrimers were dissolved and the nanoparticles coalesced to form larger nanoporous alloy particles. The pore thermal stability studied the pore stability as a function of temperature. The TEM used was a JEOL 2010F.