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Microstructure and pseudocapacitive properties of electrodes constructed of oriented NiO-TiO_2 nanotube arrays

机译：取向NiO-TiO_2纳米管阵列电极的微观结构和拟电容特性

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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.
机译：我们报告了定向NiO-TiO_2纳米管（NT）阵列作为超级电容器电极的合成和电化学性能。通过扫描和透射电子显微镜，X射线衍射和光电子能谱表征了通过对Ni-Ti合金箔进行电化学阳极氧化制备的薄膜的形貌。发现NT膜的形态，晶体结构和组成取决于制备条件（阳极氧化电压和后生长退火温度）。将刚生长的NT阵列退火至600°C的温度，将它们从非晶相转变为结晶岩盐NiO和金红石TiO_2的混合物。形态和晶体结构的变化强烈影响NT电极的电化学性能。由在600°C退火的NT膜组成的电极显示出伪电容器（氧化还原电容器）行为，包括快速的充电/放电动力学和稳定的长期循环性能。在相似的膜厚度和表面积下，基于NT的电极显示出比随机堆积的基于纳米颗粒的电极更高的倍率能力。即使在最高扫描速率（500 mV / s）下，NT电极的电容也不会比在最低扫描速率（5 mV / s）下测量的电容小很多（在12％以内）。 NT电极在高扫描速率下更快的充电/放电动力学归因于更有序的NT膜结构，这有望在充电-放电反应过程中促进电子和离子的传输。

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