Microstructure and Pseudocapacitive Properties of Electrodes Constructed of Oriented NiO-TiO₂ Nanotube Arrays

Abstract

We report on the synthesis and electrochemical properties of oriented NiO-TiO(2) nanotube (NT) arrays as electrodes for supercapacitors. The morphology of the films prepared by electrochemically anodizing Ni-Ti alloy foils was characterized by scanning and transmission electron microscopies, X-ray diffraction, and photoelectron spectroscopies. The morphology, crystal structure, and composition of the NT films were found to depend on the preparation conditions (anodization voltage and postgrowth annealing temperature). Annealing the as-grown NT arrays to a temperature of 600 °C transformed them from an amorphous phase to a mixture of crystalline rock salt NiO and rutile TiO(2). Changes in the morphology and crystal structure strongly influenced the electrochemical properties of the NT electrodes. Electrodes composed of NT films annealed at 600 °C displayed pseudocapacitor (redox-capacitor) behavior, including rapid charge/discharge kinetics and stable long-term cycling performance. At similar film thicknesses and surface areas, the NT-based electrodes showed a higher rate capability than the randomly packed nanoparticle-based electrodes. Even at the highest scan rate (500 mV/s), the capacitance of the NT electrodes was not much smaller (within 12%) than the capacitance measured at the slowest scan rate (5 mV/s). The faster charge/discharge kinetics of NT electrodes at high scan rates is attributed to the more ordered NT film architecture, which is expected to facilitate electron and ion transport during the charge-discharge reactions.

One-Dimensional Titanium Dioxide Nanomaterials: Nanotubes

“…By coating or filling the active materials on/into TiO 2 nanotubes, several groups target the fabrication of electrodes with an enhanced specific capacitance [905][906][907][908][909][910][911] .…”

NiCo2O4@TiN Core-shell Electrodes through Conformal Atomic Layer Deposition for All-solid-state Supercapacitors

“…Due to their known redox activity and natural abundance, binary transition metal oxides (TMOs) such as NiO [27,28], TiO2 [29], MnO2 [30,31], Fe2O3 [32], and Co3O4 [31,33,34] have been extensively studied as electrode materials for pseudocapacitors [35]. More recently, ternary nickel cobaltite (NiCo2O4) has attracted considerable research attention due to its low cost, environmental friendliness, and high theoretical capacitance [36][37][38][39][40].…”

Characterization of Micron-Scale Nanotublar Super Dielectric Materials

“…Although recorded during a completely different experimental protocol, one study by Kim et al [90] clearly demonstrated the typical voltage profile consistent with pseudocapacitive charge and discharge cycles. Presented here as Figure 93, the resulting "humps" on each discharge exhibit a similarity to those that are depicted in Figure 92.…”

“…Anodizing methods for creating nanofeatured films on titanium substrates have been extensively studied under a variety of similar conditions [61], [87][88][89][90][91][92][93][94]. The varying methods differ in substrate thickness, surface preparation, electrolyte composition, electrolyte concentration, anodizing potential, and anodizing duration.…”