MnO2 nanolayers on highly conductive TiO0.54N0.46 nanotubes for supercapacitor electrodes with high power density and cyclic stability

Abstract

Pseudo-capacitive MnO₂ supercapacitors are attracting intense interest because of the theoretically high specific capacitance (1370 F g⁻¹) and low cost of MnO₂. For the practical application, the power density and the cyclic stability of MnO₂-based supercapacitors are expected to be improved. Increasing the efficiency of the current collection is an effective method to improve the power density for a given supercapacitor. Here, the highly conductive and electrochemically stable material, titanium oxynitride (TiO_0.54N_0.46), is used as the current collector. Uniform amorphous MnO₂ nanolayers were deposited on metal-phase TiO_0.54N_0.46 nanotube arrays using a modified electrochemical deposition method. The resulting MnO₂ supercapacitors exhibited a high power density of 620 kW kg⁻¹ at an energy density of 9.8 W h kg⁻¹. This is comparable to high-performance carbon-based electrochemical double layer capacitors in aqueous electrolytes. The high electron transport was enhanced with a highly conductive TiO_0.54N_0.46 scaffold. Ion transport was promoted in the nanotube structures that had porous walls. In addition, the close interfacial connection between MnO₂ and TiO_0.54N_0.46 contributed to the excellent cyclic stability (ca. 92.0% capacitance retention after 100 000 cycles). These results indicated that the highly conductive and electrochemically stable titanium oxynitride is an excellent candidate for use as an electrode material in high performance supercapacitors.