Textural and Capacitive Characteristics of Hydrothermally Derived RuO2·xH2O Nanocrystallites: Independent Control of Crystal Size and Water Content

RuO2·xH2O nanoparticulates in different crystal sizes with various water contents were prepared via a hydrothermal synthesis route, successfully demonstrating the independent control of crystal size and water content of RuO2·xH2O. The crystalline and hydrous nature of hydrothermally derived RuO2·xH2O particulates not only reduces the proton diffusion resistance but also enhances the electronic conductivity for the redox transitions of active species. Novel and unique properties of hydrothermally derived RuO2·xH2O, i.e., effective inhibition of crystallite coalescence upon annealing, relatively high thermal stability, and maintenance of the original nanostructure, are attributable to the coalescence barrier of RuO2·xH2O crystallites due to the lattice energy. Maintaining/fine-tuning the original nanostructure of annealed RuO2·xH2O crystallites with high mesoporosity favors the penetration of electrolytes into the whole oxide matrix. This effect of not only reducing the proton diffusion resistance but also improving the electron pathways promotes the utilization of RuO2·xH2O in supercapacitor applications.