(134j) Synthesis of Nanoporous Palladium Powder With Controlled Pore and Particle Size for Hydrogen Storage Applications

Synthesis
of Nanoporous Palladium Powder with Controlled Pore and Particle Size for
Hydrogen Storage Applications

by Patrick
J. Cappillino, Christopher G. Jones, Khalid M. Hattar, Blythe G. Clark,
Michelle A. Hekmaty, Benjamin W. Jacobs, and David B. Robinson

Materials
capable of rapidly storing and delivering hydrogen are currently in demand for numerous
energy applications.  The high surface area exhibited by nanoporous palladium
has the potential to greatly improve its kinetics of hydrogen charge and discharge
versus nonporous metal while retaining favorable operating temperatures,
pressures, and volumetric capacity.  In addition, the void space imparted by
porosity should accommodate the volumetric expansion of palladium upon
hydriding, mitigating plastic deformation and improving cycle life.

By chemically
reducing palladium salts in the presence of various surfactants, we are able to
synthesize palladium having size-tunable mesopores from a few to tens of nm, in
a scalable fashion.  Our results suggest that Pd nanoparticles form and sinter
around micelles present in the aqueous media.  Changing the chemical
composition of the surfactant affects the size of these micelles and ultimately
determines the pore dimensions.  We demonstrate that pore size affects not only
surface area, but also pore thermal stability under vacuum, and in the presence
of hydrogen gas.

In addition
to pore geometry, particle size and shape are important factors in determining
gas flow characteristics. Using nonporous copper particles as sacrificial
reductants for palladium salts, in the presence of surfactants, we are able to synthesize
micron-sized particles of uniform size and shape.  This is in contrast to continuous
aggregates and films that are obtained using soluble chemical reductants or
planar electrodes.

We will
present details of the synthesis of nanoporous palladium, demonstrating control
of both pore and particle size.  Bulk measurements of hydrogen storage
properties and pore characteristics, as well as microscopic measurements,
including in situ heated-stage TEM under vacuum and in the presence of
hydrogen, will be included, as well as details on the kinetics of
hydriding/dehydriding.

Sandia
National Laboratories is a multi-program laboratory managed and operated by Sandia
Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the
U.S. Department of Energy's National Nuclear Security Administration under
contract DE-AC04-94AL85000.