Paper SS+NS-WeM11
Phase/Catalytic Activity Correlations of TiO₂ ALD Functionalized Nanoporous Gold

Wednesday, October 30, 2013, 11:20 am, Room 201 A

Nanoporous metals have many promising technological applications, such as catalysts, photo-catalysts, and electrodes in batteries, but their practical use is often limited by their tendency to coarsen at elevated temperatures. Here we demonstrate that atomic layer deposition (ALD) of nanometer-thick TiO₂ films can drastically improve the thermal stability and mechanical properties of nanoporous gold (np-Au) while further adding functionality—such as dramatically improved catalytic activity. Aerobic CO oxidation was used to test the effects of annealing on the catalytic activity of the TiO₂/npAu hybrid materials, and the observed changes in catalytic activity will be discussed in terms of annealing induced morphology and phase changes. We characterized these annealing-induced changes of morphology and phase composition by cross-sectional scanning electron microscopy (xSEM), x-ray photoemission spectroscopy (XPS), and near-edge x-ray absorption fine structure (NEXAFS). The Ti L_2,3-edge in NEXAFS is well known to exhibit exceptional sensitivity to Ti coordination and structure. Amorphous, anatase and rutile polymorphs of TiO₂ can be clearly distinguished and reveal a smooth and strong variation in the predominant TiO₂ phase as a function of annealing. Our results provide new insights into the thermal stability of functionalized electrodes for energy storage and harvesting applications.

This work was performed under the auspices of the US DOE by LLNL under Contract DE-AC52-07NA27344