Controlled Synthesis And Supercapacitive Performance Of Heterostructured MnO₂/H_TiO₂ Nanotube Arrays

Supercapacitors ?SCs? are a new type of efficient energy storage devices. Electrode materials are the most critical component determining the performance and the cost of the SCs. In this work, highly ordered and well-separated TiO₂ nanotube arrays ?TiO₂ NTAs? with large specific surface area were fabricated by electrochemical anodization of Ti foils. Further, a novel-structured MnO₂/H-TiO₂ NTAs electrode with superior supercapacitive performance was developed by galvanostatic electrodepositing MnO₂ nanoflakes onto both the outer and inner walls of electrochemically hydrogenated TiO₂ NTAs ?H-TiO₂ NTAs?. This work would not only expand the application of TiO₂ NTAs,but also offer theoretical and technical guideline for nanoarray-based electrodes applied for high-performance supercapacitors as well as other energy storage devices. The main research results are as follows:?1? Highly ordered and well-separated TiO₂ NTAs with large specific surface area were fabricated by electrochemical anodization of Ti foils. After annealing crystallization,the electrical properties and electrochemical performance of TiO₂ NTAs were remarkably improved by a facile and cost-effective technique of electrochemical hydrogenation. The influence of hydrogenation parameters on the conductivity and electrochemical properties of H-TiO₂ NTAs as well as the capacitance improvement mechanism were further proposed. The result shows that: the specific capacitance of H-TiO₂ NTAs fabricated at 4 V for 20 min in a 0.1 mol-L-1 Na2SO4 solution could achieve 7.5 mF cm-2 at 0.2 mA cm-2, which is almost 75 times the capacitance of TiO₂ NTAs ?0.1 mF-cm-2?.?2? A novel-structured MnO₂/H-TiO₂ NTAs electrode with superior supercapacitive performance was successfully fabricated via sequential chemical bath deposition technique. MnO₂ nanoflakes were uniformly deposited onto both the outer and inner walls of H-TiO₂ NTAs. The influence of immersion cycles on the microstructure and supercapacitance of MnO₂/H-TiO₂ NTAs were analyzed, and the result shows that the specific capacitance of MnO₂/H-TiO₂ NTAs-2 ?two cycles? could achieve 523.90 F·g-1 at a current density of 1 A g'1 as well as outstanding long-term cycling stability with only 11% reduction of initial specific capacitance at a current density of 5 A-g-1 after 1000 cycles.?3? Another type of MnO₂/H-TiO₂ NTAs electrode with superior supercapacitive performance was developed by galvanostatic electrodepositing MnO₂ nanoflakes onto both the outer and inner walls of H-TiO₂ NT As. The influence of depositing time on the microstructure and supercapacitance of MnO₂/H-TiO₂ NTAs were analyzed in detail.The result shows that the mass and size of MnO₂ increased by prolonging the deposition time. MnO₂/H-TiO₂ NTAs fabricated with 4 min as the depositin time could achieve 650.0 F-g-1 at a current density of 1 A-g-1 as well as outstanding long-term cycling stability with only 9% reduction of initial specific capacitance at a current density of 5 A·g-1 after 1000 cycles.