The enhanced adhesion between overlong TiNxOy/MnO2 nanoarrays and Ti substrate: Towards flexible supercapacitors with high energy density and long service life

Weak adhesion between anodic TiO2 nanotube arrays (TNTAs) and Ti substrate is a nonnegligible obstacle for the preparation of long TNTAs and greatly limits its practical application. The TiNxOy nanoarrays prepared from TNTAs by a high-temperature nitridation process also suffer this defect. In this work, a compact layer (similar to 140 nm in thickness) was introduced into the bottom of TNTAs via an additional anodization, resulting in firm binding between the Ti substrate and TNTAs. Owing to the strong adhesion, overlong TiNxOy nanoarrays up to 29.8 mu m without curling can be obtained. Notably, the TiNxOy nanoarrays with average lengths of similar to 22.8 mu m depict an extraordinary specific capacitance of 550.8 mF cm(-2) at 0.5 mA cm(-2) in 1.0 M H2SO4, which is the highest value of TiNxOy nanoarrays as reported so far. Moreover, TiNxOy/MnO2, TiNxOy/Co-S and TiNxOy/MoS2 nanoarrays were obtained. The loaded thin MnO2 layer presents a superior specific capacitance of 1404.4 F g(-1) at 0.5 A g(-1) (95.5 mF cm(-2) at 0.5 mF cm(-2)). Flexible symmetric supercapacitor constructed by TiNxOy/MnO2 nanoarrays can offer energy and power densities of 1.24 mu Wh cm(-2) and 9.14 mW cm(-2) at 30 mA cm(-2), respectively. Remarkably, the assembled TiNxOy/MnO2 flexible supercapacitor achieves excellent cyclic stability with a retention of 93.88% over 10000 cycles. The obtained TiNxOy/Co-S nanoarrays can offer a specific capacitance of 358 mF cm(-2) at 0.5 mA cm(-2).