(257m) Nanoporous Metal Films Formed with Aqueous Organic Templates

Nanoporous metals have the highest practical metal surface area per unit volume. They are of potential value for surface-catalyzed chemical reactions; supercapacitors; and chemical separations based on electrical potential-dependent adsorption, such as capacitive deionization. Methods to grow nanoporous metals using soft templates have been published by many groups over the past two decades, but the growth mechanisms, optimal procedures, and properties of the materials are not yet fully clarified. We will present our efforts to make progress on these problems, with emphasis on palladium. The ability of palladium to reversibly store hydrogen is of value for small-scale metal hydride batteries, as well as hydrogen gas or pH sensors. These properties also lead to unique synthetic opportunities and challenges.

We have used liquid-cell transmission electron microscopy to study the mechanisms of metal growth by chemical reduction in the presence of surfactants. Our results suggest that Pd nanoparticles form and sinter around micelles present in the aqueous phase. Changing the size of the surfactant molecules affects the size of these micelles, and ultimately determines the pore dimensions. The stability of nanopores in metals is a strong function of temperature and the chemical state of the surface. Attention to these conditions is necessary when formulating a new material or synthetic method. Reactions that transport hydrogen between nanoporous palladium and the gas or aqueous phase are significantly faster than those involving lower-surface area materials.

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. The work was funded in part by Sandiaâ??s Laboratory-directed Research and Development program. The Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy under contract DE-AC05-76RL01830. SAND2016-4362 A