Ultrahigh capacitance of TiO2 nanotube arrays/C/MnO2 electrode for supercapacitor

The development of well-ordered TiO2 nanotubes arrays (TNTAs) as a binder-free electrode in supercapacitors was hindered by their poor conductivity and low capacitance. Herein, the hierarchical structure of TNTAs/C/MnO2 (TNTCM) electrode was built via three-step process — typical anodization, carbon deposition and electrodeposition method. TiO2 nanotube arrays obtained from anodization provide a high surface area substrate for binder-free electrode, followed by carbon nanoparticles which could act as an electronic transfer medium penetrated into TNTAs using gas thermal penetration, the TNTAs/C electrode became high conductivity, then the two-dimension birnessite-type MnO2 nanoflakes were in situ growth onto TNTAs/C composites through scalable and easy electrodeposition method could storage energy by faradaic reaction. The resultant TNTCM hybrid composites manifest a remarkable specific areal capacitance of 492 mF/cm2, 207 times than that of TNTAs/C electrode, the value is comparable or much higher than those of previously reported TiO2 nanotubes-based electrode for supercapacitor. The synthesized TNTCM electrode exhibit a high energy density of 465 mWh/m2 at power density of 2.5 W/m2. In addition, the excellent energy storage performance is well maintained with a capacitance retention of 98% during 3000 charge–discharge cycles, indicating its promising application in energy storage and conversion fields.