Enhanced performance of layered titanate nanowire-based supercapacitor electrodes by nickel ion exchange

Titania nanostructured materials have been used extensively for the fabrication of electrochemical capacitors. However, the devices typically exhibit relatively low capacitance and poor cycling stability. Herein, we report the synthesis of a core-shell heterostructure based on layered titanate nanowires coated with nickel hydroxide nanosheets on a titanium mesh, referred to as K2Ti4O9@Ni(OH)2/Ti, by a simple nickel ion exchange reaction. The incorporation of nickel into the titanate nanowires is confirmed by X-ray photoelectron spectroscopic measurements and elemental mapping. Scanning electron microscopic and transmission electron microscopic measurements show the formation of a highly porous network of the hybrid nanowires. Electrochemical studies show that the K2Ti4O9@Ni(OH)2/Ti electrodes possess a high specific capacitance of 340 mF/cm(2) at 50 mV/s in an aqueous electrolyte of 3 M KOH and 3 mF/cm(2) at 0.04 mA/cm(2) in the KOH/PVA solid-state electrolyte, with an excellent retention rate of 92.5% after 2000 cycles and 92.7% after 10 000 cycles, respectively. Such a performance is a few tens of times better than that of the unmodified K2Ti4O9/Ti electrode. The enhanced capability of the chemically modified titanate electrodes may open up new opportunities in the development of low-cost, high-performance, and flexible supercapacitors.