Electrochemical and textural characterization of binary Ru-Sn oxides synthesized under mild hydrothermal conditions for supercapacitors

Hydrous ruthenium-tin oxides (denoted as (Ru-Sn)O₂·nH₂O) were synthesized under a mild hydrothermal condition. The mean particles size of pristine RuO₂·nH₂O, smaller than 3 nm, was decreased with the introduction of Sn into the precursor solutions while it is not significantly affected by varying the Sn content. The textual characteristics of (Ru-Sn)O₂·nH₂O were analyzed through means of X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), electron diffraction, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analyses (TGA). From the ideal capacitive behavior of pristine oxides with the Ru content ≥40 at.%, hydrothermal synthesis favored the formation of hydrous oxides with a novel structure providing excellent pathways for electron hopping and proton diffusion/exchange during the charge storage/delivery process. The introduction of tin oxide was demonstrated to successfully promote the utilization of oxyruthenium species, reaching a maximum C_S,Ru of ca. 830 F/g for pristine Ru_0.6Sn_0.4O₂·nH₂O (measured at 25 mV/s).