No abstract

A general template-assisted electrochemical approach was used to synthesize three-dimensional ordered Ni core-NiO shell inverse opals (IOs) as electrodes for supercapacitors. The Ni-NiO IO electrodes displayed pseudo-capacitor behavior, good rate capability and cycling performance.

Three-dimensional, ordered macroporous materials such as inverse opal structures are attractive materials for various applications in electrochemical devices because of the benefits derived from their periodic structures: relatively large surface areas, large voidage, low tortuosity and interconnected macropores. However, a direct application of an inverse opal structure in membrane electrode assemblies has been considered impractical because of the limitations in fabrication routes including an unsuitable substrate. Here we report the demonstration of a single cell that maintains an inverse opal structure entirely within a membrane electrode assembly. Compared with the conventional catalyst slurry, an ink-based assembly, this modified assembly has a robust and integrated configuration of catalyst layers; therefore, the loss of catalyst particles can be minimized. Furthermore, the inverse-opalstructure electrode maintains an effective porosity, an enhanced performance, as well as an improved mass transfer and more effective water management, owing to its morphological advantages.

Straight-stranded anatase TiO2 nanotubes were produced by anodic oxidation on a pure titanium substrate in an aqueous solution containing a 0.45 wt % NaF electrolyte (pH 4.3 fixed). The average length of the TiO2 nanotubes was approximately 3 μm, which had an effect on the level of dye adsorption in the dye-sensitized solar cells. The anodic TiO2 nanotubes were applied as a working electrode in a solid-state dye-sensitized solar cell. An approximately 1 nm ZnO shell was coated on the TiO2 nanotube to improve the open-circuit voltage (V oc) and conversion efficiency of the solar cell, and to retard any back reaction. Although the V oc and short-circuit current (J sc) of the cell were improved, there was a low fill factor as a result of the formation of a thick TiO2 barrier layer in the anodic TiO2/Ti substrate. A parameter on the degradation of fill factor (37%) is related to the formation of a thick TiO2 barrier layer in the anodic TiO2/Ti substrate interface. A hydrogen peroxide treatment was performed in an attempt to narrow the TiO2 barrier layer. This treatment was found to influence not only fill factor (37−49%) but also the conversion efficiency (0.704−0.906%) of the cell by eliminating the remnant after anodic reaction and barrier narrowing through an etching effect. This result was confirmed by X-ray photoelectron spectroscopy (XPS) and photocurrent-voltage measurements. The longer electron lifetime on the ZnO coated TiO2 film was measured by the open-circuit voltage decay. The improvement in the electron lifetime from the thin ZnO coating affects the number of electrons collected on the Ti substrate and the retardation of charge recombination. Therefore, the ZnO coating on the TiO2 nanotube film improves the efficiency of dye-sensitized TiO2 solar cells from the extended V oc from ZnO coating confirmed by the Mott−Schottky plots and the increased J sc through the inhibition of charge recombination confirmed by IPCE measurements.