教師著作
Permanent URI for this collectionhttp://rportal.lib.ntnu.edu.tw/handle/20.500.12235/37076
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Item Vitalizing fuel cells with vitamins: pyrolyzed vitamin B12 as a non-precious catalyst for enhanced oxygen reduction reaction of polymer electrolyte fuel cells(Royal Society of Chemistry, 2012-01-01) S.-T. Chang; C.-H. Wang; H.-Y. Du; H.-C.Hsu; C.-M. Kang; Chia-Chun Chen; J.C.-S. Wu; S.-C. Yen; W.-F. Huang; L.-C. Chen; M.-C. Lin; K.-H. ChenThe limited natural abundance and high cost of Pt has been a major barrier in its applications for hydrogen or methanol fuel cells. In this work, based on the pyrolyzed corrin structure of vitamin B12 (py-B12/C), it is reported to produce superior catalytic activity in the oxygen reduction reaction (ORR) with an electron transfer number of 3.90, which is very close to the ideal case of 4. The H2–O2fuel cell using py-B12/C provides a maximum power density of 370 mW cm−2 and a current density of 0.720 A cm−2 at 0.5 V at 70 °C. Calculations based on density functional theory suggests that the corrin complex with a low-symmetric structure offers a much preferable path for the ORR, which is not applicable to the porphyrin with a high-symmetric structure. The long-term stability and high ORR activity of py-B12/C make it a viable candidate as a Pt-substitute in the ORR.Item Efficient Light Harvesting by Photon Downconversion and Light Trapping in Hybrid ZnS Nanoparticles/Si Nanotips Solar Cells(American Chemical Society, 2010-10-26) C.-Y. Huang; D.-Y. Wang; C.-H. Wang; Y.-T. Chen; Y.-T. Wang; Y.-T. Jiang; Y.-J. Yang; Chia-Chun Chen; Y.-F. ChenA hybrid colloidal ZnS nanoparticles/Si nanotips p−n active layer has been demonstrated to have promising potential for efficient solar spectrum utilization in crystalline silicon-based solar cells. The hybrid solar cell shows an enhancement of 20% in the short-circuit current and approximately 10% in power conversion efficiency compared to its counterpart without integrating ZnS nanoparticles. The enhancement has been investigated by external quantum efficiency, photoluminescence excitation spectrum, photoluminescence, and reflectance to distinct the role of ZnS quantum dots for light harvesting. It is concluded that ZnS nanoparticles not only act as frequency downconversion centers in the ultraviolet region but also serve as antireflection coating for light trapping in the measured spectral regime. Our approach is ready to be extended to many other material systems for the creation of highly efficient photovoltaic devices.Item Efficient light harvesting and carrier transport in PbS quantum dots/silicon nanotips heterojunctions(IOP Publishing, 2011-03-02) C.-Y. Huang; D.-Y. Wang; C.-H. Wang; Y.-T. Wang; Y.-T. Jiang; Y.-J. Yang; Chia-Chun Chen; Y.-F. ChenLight harvesting from nanocomposites consisting of silicon (Si) nanotips and PbS quantum dots (QDs) has been investigated. We show that Si nanotips provide direct carrier transport paths, additional interfacial area and light trapping. We observe that there is a dramatic enhancement in short-circuit current (from 9.34 to 14.17 mA cm−2) with nanotips structure than that of the bulk Si wafer. In addition, with an additional electron blocking layer, the photovoltaic performance can be further increased. The nanocomposites consisting of QDs and Si nanotips therefore open a promising route for efficient light harvesting from visible to infrared with improved power conversion efficiency.Item Direct evidence of type II band alignment in nanoscale P3HT/CdSe heterostructures(IOP Publishing, 2011-02-11) C.-H. Wang; C.-W. Chen; Y.-T. Chen; C.-T. Chen; Y.-F.Chen; S.-W. Chou; Chia-Chun ChenDue to inherent advantages of both constituent materials, organic/inorganic hybrid composites have attracted increasing attention. One of the fundamental issues needed to be resolved is their band alignment, which governs most of the electrical and optical properties. Here, we report the investigation of optical transition in poly(3-hexylthiophene) (P3HT)/CdSe nano-composites (NCs). It is found that the relaxation dynamics of photo-carriers in NCs is dominated by charge separation effects. Based on the band bending effect and the quantum confinement energy of electrons in the conduction band of CdSe quantum dots, we provide direct evidence of type II band alignment in P3HT/CdSe NCs. The establishment of a type II transition in NCs is very useful for the future design of efficient optoelectronic devices based on conjugated polymer/semiconductor hybrid systems.Item Low methanol-permeable polyaniline/Nafion composite membrane for direct methanol fuel cells(Elsevier, 2009-05-15) C.-H. Wang; Chia-Chun Chen; H.-C. Hsu; H.-Y. Du; C.-R. Chen; J.-Y. Hwang; L.-C. Chen; H.-C. Shih; J. Stejskal; K.-H. ChenProtonated polyaniline (PANI) is directly polymerized on Nafion 117 (N117), forming a composite membrane, to act as a methanol-blocking layer to reduce the methanol crossover in the direct methanol fuel cell (DMFC), which is beneficial for the DMFC operating at high methanol concentration. The PANI layer grown on the N117 with a thickness of 100 nm has an electrical conductivity of 13.2 S cm−1. The methanol permeability of the PANI/N117 membrane is reduced to 59% of that of the N117 alone, suggesting that the PANI/N117 can effectively reduce the methanol crossover in the DMFC. Comparison of membrane-electrode-assemblies (MEA) using the conventional N117 and the newly developed PANI/N117 composite shows that the PANI/N117-based MEA outputs higher power at high methanol concentration, while the output power of the N117-based MEA is reduced at high methanol concentration due to the methanol crossover. The maximum power density of the PANI/N117-based MEA at 60 °C is 70 mW cm−2 at 6 M methanol solution, which is double the N117-based MEA at the same methanol concentration. The resistance of PANI/N117 composite membrane is reduced at elevated methanol concentration, due to the hydrogen bonding between methanol and PANI pushes the polymer chains apart. It is concluded that the PANI/N117-based MEA performs well at elevated methanol concentration, which is suitable for the long-term operation of the DMFC.