Local structure distortion induced by Ti dopants boosting the pseudocapacitance of RuO2-based supercapacitors

Abstract

Binary oxides with atomic ratios of Ru/Ti = 90/10, 70/30, and 50/50 were fabricated using H₂O₂-oxidative precipitation with the assistance of a cetyltrimethylammonium bromide (CTAB) template, followed by a thermal treatment at 200 °C. The characteristics of electron structure and local structure extracted from X-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM) analyses indicate that incorporation of Ti into the RuO₂ lattice produces not only the local structural distortion of the RuO₆ octahedra in (Ru–Ti)O₂ with an increase in the central Ru–Ru distance but also a local crystallization of RuO₂. Among the three binary oxides studied, (Ru₇₀–Ti₃₀)O₂ exhibits a capacitance improvement of about 1.4-fold relative to the CTAB-modified RuO₂, mainly due to the enhanced crystallinity of the distorted RuO₆ structure rather than the surface area effect. Upon increasing the extent of Ti doping, the deteriorated supercapacitive performance of (Ru₅₀–Ti₅₀)O₂ results from the formation of localized nano-clusters of TiO₂ crystallites. These results provide insight into the important role of Ti doping in RuO₂ that boosts the pseudocapacitive performance for RuO₂-based supercapacitors. The present result is crucial for the design of new binary oxides for supercapacitor applications with extraordinary performance.