Enhanced Supercapacitive Properties of Mixed Oxide Nanotubes Grown by Anodization of Ti-Fe Alloys

Like titanium metal, nanotube array films can be grown on Ti alloys by anodization in fluoride-containing electrolytes. Further, the anodization of Ti alloys provide a unique pathway to dope TiO2 nanotubes with the alloying element. However, the details of anodization behaviors of Ti alloys and the obtained nanotubes for application in supercapacitors remain poorly understood. Herein, three Ti-Fe alloys containing different amounts of Fe element (10, 15, and 20 wt%) are fabricated by using a vacuum arc melting furnace. Their anodization behaviors are systematically investigated. The nanotube array films can be achieved on these alloys, which are composed of TiO2, Fe2O3, and Fe-doped TiO2. Their electrochemical behaviors are completely different from both the pure TiO2 and the pure Fe2O3. The mixed oxide nanotubes on Ti-15 wt%Fe have the maximum capacitance among the three Ti-Fe alloys, which is 3.75 times higher than that of pure TiO2. Moreover, the mixed oxide electrode exhibits high rate capability and excellent cycling stability with only 5.7% loss in capacitance over 10 000 cycles. The presented results suggest that the alloy anodization is an efficient strategy for enhancing the performance of TiO2 electrode materials for supercapacitors.