Proton NMR and dynamic studies of hydrous ruthenium oxide

A series of hydrous ruthenium oxide (RuO2.xH(2)O) samples annealed at different temperatures have been studied by solid-state H-1 NMR spectroscopy. The proton dynamics of the RuO2.xH(2)O samples was characterized for the first time through variable-temperature H-1 spin-lattice relaxation time (T-1) measurements. For the RuO2.xH(2)O samples annealed at temperatures lower than 100 degreesC and higher than 200 degreesC, 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 degreesC 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 Ru2+, Ru-3+,Ru- and Ru4+ valency states in the local structure of the RuO2.xH(2)O is crucial for hydrogen transfer and storage ability.