Fabrication of TiO2-Nanotube-Array-Based Supercapacitors

In this work, a simple and cost-effective electrochemical anodization technique was adopted to rapidly grow TiO₂ nanotube arrays on a Ti current collector and to utilize the synthesized materials as potential electrodes for supercapacitors. To accelerate the growth of the TiO₂ nanotube arrays, lactic acid was used as an electrolyte additive. The as-prepared TiO₂ nanotube arrays with a high aspect ratio were strongly adhered to the Ti substrate. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results confirmed that the TiO₂ nanotube arrays were crystallized in the anatase phase. TEM images confirmed the nanotublar-like morphology of the TiO₂ nanotubes, which had a tube length and a diameter of ~16 and ~80 nm, respectively. The electrochemical performance of the TiO₂ nanotube array electrodes was evaluated using the cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge (GCD) measurements. Excellent electrochemical response was observed for the electrodes based on the TiO₂ nanotube arrays, as the cells delivered a high specific capacitance of 5.12 mF/cm² at a scan rate of 100 mV/s and a current density of 100 μA/cm². The initial capacity was maintained for more than 250 cycles. Further, a remarkable rate capability response was observed, as the cell retained 88% of the initial areal capacitance when the scan rate was increased from 10 to 500 mV/s. The results suggest the suitability of TiO₂ nanotube arrays as electrode materials for commercial supercapacitor applications

Design of a trigonal halide superionic conductor by regulating cation order-disorder

Lithium-metal-halides have emerged as a class of solid electrolytes that can deliver superionic conductivity comparable to that of state-of-the-art sulfide electrolytes, as well as electrochemical stability that is suitable for high-voltage (>4 volt) operations. We show that the superionic conduction in a trigonal halide, such as Li3MCl6 [where metal (M) is Y or Er], is governed by the in-plane lithium percolation paths and stacking interlayer distance. These two factors are inversely correlated with each other by the partial occupancy of M, serving as both a diffusion inhibitor and pillar for maintaining interlayer distance. These findings suggest that a critical range or ordering of M exists in trigonal halides, and we showcase the achievement of high ionic conductivity by adjusting the simple M ratio (per Cl or Li). We provide general design criteria for superionic trigonal halide electrolytes.11Nsciescopu