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Trapping a Ru₂O₃ Corundum-like Structure at Ultrathin, Disordered RuO₂ Nanoskins Expressed in 3D
- Donakowski, Martin D., Mansour, Azzam N., Pala, Irina R., Chervin, Christopher N., DeSario, Paul A., Long, Jeffrey W., Rolison, Debra R.
- Journal of physical chemistry 2018 v.122 no.50 pp. 28895-28900
- X-radiation, X-ray absorption spectroscopy, aerogels, capacitance, carbon, electrical conductivity, heat treatment, nanocrystals, physical chemistry, ruthenium, silica, temperature
- 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 Å 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 Å, 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.