Highly active ruthenium oxide coating via ALD and electrochemical activation in supercapacitor applicationsElectronic supplementary information (ESI) available. See DOI: 10.1039/c5ta03742e

Highly active ruthenium oxide was uniformly coated on vertically aligned carbon nanotube forests for pseudocapacitor electrodes in enhanced energy storage applications. Atomic layer deposition (ALD) was designed to realize the conformal coating process onto porous structures and an electrochemical oxidation process was developed to achieve highly active ruthenium oxide. Results show 100× and 170× higher specific capacitance after the ALD coating and further electrochemical oxidation process, respectively, as compared with that of pure CNT electrodes. Furthermore, the measured capacitance value was close to the theoretical limit of ruthenium oxide at 644 F g −1 with a high power density at 17 kW kg −1 . The electrode performance was tested over 10 000 charge-discharge cycles with gradually improved capacitance of 17% higher than the starting value and at ultra-high scan rates of up to 20 V s −1 . Vertically aligned CNTs exhibit 100× and 170× higher capacitance when coated with ALD RuO x and after further electrochemical oxidation, respectively.