Study of the pore size effect on the charge storage of hydrous RuO2 nanoparticles supported within the pores of activated carbon

Abstract

Hydrous ruthenium oxide (RuO2) nanoparticles are hybridized inside the pores of activated carbon (AC) for preparing electrochemical capacitor electrodes. The hybridization consists of the adsorption of an organoruthenium complex and subsequent heat treatment to reduce the complex into Ru nanoparticles within the AC pores, followed by the electrochemical oxidation of the resulting Ru nanoparticles into hydrous RuO2 nanoparticles. Two kinds of AC with only micropores and both micropores and mesopores of ~4 nm are examined to study the effects of pore sizes on the charge/discharge characteristics of the AC/RuO2 hybrids. Since the introduction of hydrous RuO2 nanoparticles is not accompanied by the volumetric expansion of the AC particles, the volumetric capacity is enhanced in comparison with the pristine AC. However, the capacitance retention at high charge/discharge rates is decreased by micropores or an excessive amount of the hydrous RuO2 nanoparticles. This method is free from the use of any organic solvent, concomitant solvent removal and drying process, or reducing and oxidizing reagents, and therefore, can be used to synthesize porous carbon/metal oxide nanoparticle hybrids for versatile applications.