37,200 research outputs found
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Department of Energy Engineering (Energy Engineering)Solid oxide fuel cells (SOFCs) are recognized as next generation environmentally friendly energy conversion devices due to their high energy conversion efficiency, fuel flexibility, efficient reclamation of waste heat, and low pollutant emissions. Nevertheless, the commercialization of SOFCs has been impeded by reason of some issues associated with the high operating temperatures (800-1000oC) such as undesired reactions between cell components, high cost, and material compatibility challenges. Thus, reducing the operating temperatures toward an intermediate
temperature range (600-800oC) is essential to overcome the aforementioned problems. In intermediate temperature SOFCs (IT-SOFCs), however, electrocatalytic activity toward oxygen reduction reaction at the cathode is significantly decreased, which in turn causes insufficient fuel cell performance. Current researches, therefore, have been focused on enhancing the performance of cathode for effective IT-SOFC operation.
In this regard, the infiltration method could be an excellent cathode fabrication method, considering its outstanding advantages toward intermediate temperature operation. First, each optimized sintering temperature of cathode and electrolyte can be applied, ensuring the favorable characteristics for IT-SOFC operation. Second, due to relatively low sintering temperature, nano structured cathodes can be formed, resulting in enlarged surface area and enhancement of electrochemical performance. Finally, long term stability is improved because the thermal expansion coefficient between cathode and electrolyte is minimized.
This thesis mainly focuses on the fabrication of SOFC cathode by the infiltration method to achieve high fuel cell performance in the intermediate temperature range. Herein, my research paper studying infiltrated cathode materials for IT-SOFC is presented as follows.
- A Nano-structured SOFC Composite Cathode Prepared via Infiltration of La0.5Ba0.25Sr0.25Co0.8Fe0.2O3-?? into La0.9Sr0.1Ga0.8Mg0.2O3-?? for Extended Triple Phase Boundary Areaclos
Spatially controlled electrostatic doping in graphene p-i-n junction for hybrid silicon photodiode
Sufficiently large depletion region for photocarrier generation and
separation is a key factor for two-dimensional material optoelectronic devices,
but few device configurations has been explored for a deterministic control of
a space charge region area in graphene with convincing scalability. Here we
investigate a graphene-silicon p-i-n photodiode defined in a foundry processed
planar photonic crystal waveguide structure, achieving visible - near-infrared,
zero-bias and ultrafast photodetection. Graphene is electrically contacting to
the wide intrinsic region of silicon and extended to the p an n doped region,
functioning as the primary photocarrier conducting channel for electronic gain.
Graphene significantly improves the device speed through ultrafast out-of-plane
interfacial carrier transfer and the following in-plane built-in electric field
assisted carrier collection. More than 50 dB converted signal-to-noise ratio at
40 GHz has been demonstrated under zero bias voltage, with quantum efficiency
could be further amplified by hot carrier gain on graphene-i Si interface and
avalanche process on graphene-doped Si interface. With the device architecture
fully defined by nanomanufactured substrate, this study is the first
demonstration of post-fabrication-free two-dimensional material active silicon
photonic devices.Comment: NPJ 2D materials and applications (2018
In situ interface engineering for probing the limit of quantum dot photovoltaic devices.
Quantum dot (QD) photovoltaic devices are attractive for their low-cost synthesis, tunable band gap and potentially high power conversion efficiency (PCE). However, the experimentally achieved efficiency to date remains far from ideal. Here, we report an in-situ fabrication and investigation of single TiO2-nanowire/CdSe-QD heterojunction solar cell (QDHSC) using a custom-designed photoelectric transmission electron microscope (TEM) holder. A mobile counter electrode is used to precisely tune the interface area for in situ photoelectrical measurements, which reveals a strong interface area dependent PCE. Theoretical simulations show that the simplified single nanowire solar cell structure can minimize the interface area and associated charge scattering to enable an efficient charge collection. Additionally, the optical antenna effect of nanowire-based QDHSCs can further enhance the absorption and boost the PCE. This study establishes a robust 'nanolab' platform in a TEM for in situ photoelectrical studies and provides valuable insight into the interfacial effects in nanoscale solar cells
Van der Waals Materials for Atomically-Thin Photovoltaics: Promise and Outlook
Two-dimensional (2D) semiconductors provide a unique opportunity for
optoelectronics due to their layered atomic structure, electronic and optical
properties. To date, a majority of the application-oriented research in this
field has been focused on field-effect electronics as well as photodetectors
and light emitting diodes. Here we present a perspective on the use of 2D
semiconductors for photovoltaic applications. We discuss photonic device
designs that enable light trapping in nanometer-thickness absorber layers, and
we also outline schemes for efficient carrier transport and collection. We
further provide theoretical estimates of efficiency indicating that 2D
semiconductors can indeed be competitive with and complementary to conventional
photovoltaics, based on favorable energy bandgap, absorption, external
radiative efficiency, along with recent experimental demonstrations. Photonic
and electronic design of 2D semiconductor photovoltaics represents a new
direction for realizing ultrathin, efficient solar cells with applications
ranging from conventional power generation to portable and ultralight solar
power.Comment: 4 figure
Nanoantennas for visible and infrared radiation
Nanoantennas for visible and infrared radiation can strongly enhance the
interaction of light with nanoscale matter by their ability to efficiently link
propagating and spatially localized optical fields. This ability unlocks an
enormous potential for applications ranging from nanoscale optical microscopy
and spectroscopy over solar energy conversion, integrated optical
nanocircuitry, opto-electronics and density-ofstates engineering to
ultra-sensing as well as enhancement of optical nonlinearities. Here we review
the current understanding of optical antennas based on the background of both
well-developed radiowave antenna engineering and the emerging field of
plasmonics. In particular, we address the plasmonic behavior that emerges due
to the very high optical frequencies involved and the limitations in the choice
of antenna materials and geometrical parameters imposed by nanofabrication.
Finally, we give a brief account of the current status of the field and the
major established and emerging lines of investigation in this vivid area of
research.Comment: Review article with 76 pages, 21 figure
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