Proton NMR and Dynamic Studies of Hydrous Ruthenium Oxide

A series of hydrous ruthenium oxide (RuO 2 · x H 2 O) samples annealed at different temperatures have been studied by solid-state 1 H NMR spectroscopy. The proton dynamics of the RuO 2 · x H 2 O samples was characterized for the first time through variable-temperature 1 H spin−lattice relaxation time ( T 1 ) measurements. For the RuO 2 · x H 2 O samples annealed at temperatures lower than 100 °C and higher than 200 °C, a high proton activation energy was obtained, implying that the proton dynamics/diffusive motion is relatively restrained, whereas the samples annealed at temperatures between 100 and 200 °C exhibited relatively low proton activation energies, indicating that the protons can easily diffuse into the bulk of the material. Therefore, the proton activation energy correlates strongly with the hydrogen transfer and storage ability of the proton-conducting materials. In combination with electrochemical measurements, our NMR data also suggest that the coexistence of the Ru 2+, Ru 3+, and Ru 4+ valency states in the local structure of the RuO 2 · x H 2 O is crucial for hydrogen transfer and storage ability.