• Long, Jeffrey W.
• Mansour, Azzam N.
• Donakowski, Martin D.
• Rolison, Debra R.
• Chervin, Christopher N.
• Pala, Irina R.
• Desario, Paul

Abstract

Protocols that express functional materials in a way that amplifies their surface-to-volume ratio offer a means to probe the structural ambiguity and surface-mediated reactivity of technologically important materials. We previously reported that three-dimensional (3D) ultraporous scaffolds, such as silica aerogels, silica fiber paper, and carbon nanofoam paper (CNF), provide a form factor that expresses energy-storing, catalytic ruthenium oxide (RuOx) as essentially all-surface—and a highly disordered one at that. To track the chemical state and solid-state structure of the 3D-expressed RuOx nanoskins as a function of thermal processing, we use X-ray near-edge structure (XANES), extended X-ray fine structure (EXAFS), and differential pair-distribution function (DPDF) analyses. We find that a Ru-centered ∼2.4 A correlation present in the as-deposited oxide, also observed in PDF analysis of RuO₂·nH₂O but previously unassigned, fits the metastable corundum-like Ru₂O₃ structure. This corundum-like feature diminishes in concentration with increasing treatment temperature (25–200 °C), commensurate with an increase in relative rutile RuO₂ content, electrical conductivity, and charge-storing capacitance of the oxide. Yet disorder persists beyond 8 A, and a rutile nanocrystalline structure is not attained until >200 °C. The combination of synthetic amplification and total scattering analyses offers a viable approach to elucidate the structural ambiguity of practical, disordered nanomaterials.

Topics

• impedance spectroscopy
• surface
• Carbon
• electrical conductivity
• Ruthenium
• extended X-ray absorption fine structure spectroscopy