A lightweight 200‐W direct methanol fuel cell (DMFC) stack was developed to power a small‐scale unmanned aerial vehicle (UAV). To reduce the weight and volume of the DMFC stack, carbon‐composite bipolar plates were fabricated using natural graphite, phenolic resin, and carbon black. In addition, lightweight end plates, bolts, and nuts were fabricated using polyetheretherketone (PEEK) materials. The lightweight DMFC stack, which was designed for small UAV operating under cruising conditions, consisted of 33 cells, in which membrane‐electrode assemblies (MEAs) with active area of 88 cm2 were stacked with the composite bipolar plates. The DMFC stack was first evaluated under various methanol feed concentrations. It produced a maximum power of 251 W at 13.4 V and 71.3 °C under methanol feed concentration of 2 M. Thereafter, the DMFC stack was integrated with a Li‐polymer battery as an auxiliary power source, and the load‐sharing characteristics of the UAV propulsion system were tested under actual flight mode comprising takeoff, cruising, and landing. The flight test results showed that the lightweight DMFC stack successfully delivered full power for cruise flight, whereas the battery provided the additional power required during takeoff. This work successfully demonstrated that the DMFC technology can be applied to small‐scale UAVs.
Crack-free large area photonic crystals have been fabricated
using
colloidal silica spheres modified the surface with vinyltriethoxysilane
(VTES) and an in situ photo-cross-linking (ISPL) process during the
self-assembly of the surface modified spheres (SMS). The VTES has
been covalently attached on the surface of the silica spheres by hydrolysis
and condensation reactions. The weight ratios of the VTES and the
spheres are 1:7 (VTES-A), 2:7 (VTES-B), and 3:7 (VTES-C). The Fourier
transform infrared (FTIR) absorption peak attributed to the −OH
bond stretching vibration shifts from 3230 to 3480 cm–1 with increasing the amount of VTES. The characteristic absorption
peaks of −CH and −CH2 appeared at 2853, 2956,
and 3023 cm–1 for VTES-C. The absorption peat at
1409 cm–1 representing the −CH deformation
vibration increased with the increase of the amount
of VTES. The stop bands are shown at 655, 693, and 708 nm for VTES-A,
VTES-B, and VTES-C, respectively. The stop
band shift toward longer wavelength is mainly due to the increase
of the effective refractive index. The characteristic absorption peak
−CH2–CH3 increased drastically
after the ISPL
process and the
washing process due to the stronger absorption intensity of the −CH2–CH3 compared with the absorption intensity
of −CHCH2. Although the photonic crystal
constructed with pure
silica spheres has cracks between the clusters, the photonic crystal
fabricated with SMS with VTES and the ISPL process during the self-assembly
of the silica spheres shows no crack in large area. This result provides
the fabrication method of a large area and stable photonic crystal
without cracks.
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