Three-Dimensional Nanoarchitecture of BiFeO₃ Anchored TiO₂ Nanotube Arrays for Electrochemical Energy Storage and Solar Energy Conversion

Abstract

Here, we report the synthesis of TiO 2 /BiFeO 3 nano-heterostructure (NH) arrays by anchoring BiFeO 3 (BFO) nanoparticles on TiO 2 nanotube surface and investigate their pseudocapacitive and photo-electrochemical properties considering their applications in green energy fields. The unique TiO 2 /BFO NHs have been demonstrated both as energy conversion and storage material. Capacitive behavior of the NHs has found to be significantly higher than the pristine TiO 2 NTs which is mainly due to the anchoring of redox active BFO nanoparticles.Specific capacitance of about 440 F g -1 has been achieved for this NHs at a current density of 1.1 Ag -1 with ~ 80% capacity retention at a current density of 2.5 A g -1 . The NHs also exhibit high energy and power performance (energy density of 46.5 Wh kg -1 and power density of 1.2 kW kg -1 at a current density of 2.5 Ag -1 ) with moderate cycling stability (92 % capacity retention after 1200 cycles). Photo-electrochemical investigation reveals that the photo current density of the NHs is almost 480% higher than the corresponding dark current and it shows significantly improved photo switching performance as compared to pure TiO 2 nanotubes which has been demonstrated based the interfacial type-II band alignment between TiO 2 and BFO.INTRODUCTION. Intensive research attention has been focused on the energy storage and conversion from the renewable and clean energy sources in order to deal with the ever-increasing energy consumption and environmental issues. 1, 2 Recently, hybrid supercapacitors (SCs) having high energy and high power density, which can bridge the gap between rechargeable battery and ordinary dielectric capacitor, are being considered to be one of the pioneers in the field of alternative energy storage systems in lieu of the conventional rechargeable battery and fuel-cell to quench the energy-thirst of the battery powered electronic gadgets, hybrid vehicles, mechatronic systems and medical instruments. 3, 4 Among SCs, the pseudocapacitors have gained remarkable attention because of their high theoretical specific capacitance, high energy and power density and long life cycle associated with Faradaic redox reactions compared to the electrical double-layer capacitors (EDLCs). 5-8 Being inspired by the high pseudocapacitance of various transition metal oxides such as MnO 2 , Fe 2 O 3 , NiO, Co 3 O 4 , NiCo 2 O 4 and V 2 O 5 , they have been studied extensively as promising candidates for SC electrodes which are also economical, environment friendly, abundant in nature and can be fabricated using easy, cost-effective routes.suitable band gap of BFO to absorb visible light efficiently and also the type II heterojunction formation due to the interface engineering which helps the generation/separation of free charge carriers (electron-hole pairs) allowing unidirectional current flow. This study indicates that the arrays of TiO 2 /BFO nano-heterostructure with enhanced capacitive and photo-electrochemical performance holds potential for applications in both renewable en...

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