67 research outputs found
Monolithic Photoelectrochemical Device for Direct Water Splitting with 19% Efficiency
Recent rapid progress in efficiencies for solar water splitting by
photoelectrochemical devices has enhanced its prospects to enable storable
renewable energy. Efficient solar fuel generators all use tandem photoelectrode
structures, and advanced integrated devices incorporate corrosion protection
layers as well as heterogeneous catalysts. Realization of near thermodynamic
limiting performance requires tailoring the energy band structure of the
photoelectrode and also the optical and electronic properties of the surface
layers exposed to the electrolyte. Here, we report a monolithic device
architecture that exhibits reduced surface reflectivity in conjunction with
metallic Rh nanoparticle catalyst layers that minimize parasitic light
absorption. Additionally, the anatase TiO2 protection layer on the photocathode
creates a favorable internal band alignment for hydrogen evolution. An initial
solar-to-hydrogen efficiency of 19.3 % is obtained in acidic electrolyte and an
efficiency of 18.5 % is achieved at neutral pH condition (under simulated
sunlight)
Photon Management in Two-Dimensional Disordered Media
Elaborating reliable and versatile strategies for efficient light coupling
between free space and thin films is of crucial importance for new technologies
in energy efficiency. Nanostructured materials have opened unprecedented
opportunities for light management, notably in thin-film solar cells. Efficient
coherent light trapping has been accomplished through the careful design of
plasmonic nanoparticles and gratings, resonant dielectric particles and
photonic crystals. Alternative approaches have used randomly-textured surfaces
as strong light diffusers to benefit from their broadband and wide-angle
properties. Here, we propose a new strategy for photon management in thin films
that combines both advantages of an efficient trapping due to coherent optical
effects and broadband/wide-angle properties due to disorder. Our approach
consists in the excitation of electromagnetic modes formed by multiple light
scattering and wave interference in two-dimensional random media. We show, by
numerical calculations, that the spectral and angular responses of thin films
containing disordered photonic patterns are intimately related to the in-plane
light transport process and can be tuned through structural correlations. Our
findings, which are applicable to all waves, are particularly suited for
improving the absorption efficiency of thin-film solar cells and can provide a
novel approach for high-extraction efficiency light-emitting diodes
Assessment of Application Technology of Natural User Interfaces in the Creation of a Virtual Chemical Laboratory
Geomorphic and stratigraphic evidence for an unusual tsunami or storm a few centuries ago at Anegada, British Virgin Islands
© The Author(s), 2010. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Natural Hazards 63 (2012): 51-84, doi:10.1007/s11069-010-9622-6.Waters from the Atlantic Ocean washed southward across parts of Anegada, east-northeast of Puerto Rico, during a singular event a few centuries ago. The overwash, after crossing a fringing coral reef and 1.5 km of shallow subtidal flats, cut dozens of breaches through sandy beach ridges, deposited a sheet of sand and shell capped with lime mud, and created inland fields of cobbles and boulders. Most of the breaches extend tens to hundreds of meters perpendicular to a 2-km stretch of Anegada’s windward shore. Remnants of the breached ridges stand 3 m above modern sea level, and ridges seaward of the breaches rise 2.2–3.0 m high. The overwash probably exceeded those heights when cutting the breaches by overtopping and incision of the beach ridges. Much of the sand-and-shell sheet contains pink bioclastic sand that resembles, in grain size and composition, the sand of the breached ridges. This sand extends as much as 1.5 km to the south of the breached ridges. It tapers southward from a maximum thickness of 40 cm, decreases in estimated mean grain size from medium sand to very fine sand, and contains mud laminae in the south. The sand-and-shell sheet also contains mollusks—cerithid gastropods and the bivalve Anomalocardia—and angular limestone granules and pebbles. The mollusk shells and the lime-mud cap were probably derived from a marine pond that occupied much of Anegada’s interior at the time of overwash. The boulders and cobbles, nearly all composed of limestone, form fields that extend many tens of meters generally southward from limestone outcrops as much as 0.8 km from the nearest shore. Soon after the inferred overwash, the marine pond was replaced by hypersaline ponds that produce microbial mats and evaporite crusts. This environmental change, which has yet to be reversed, required restriction of a former inlet or inlets, the location of which was probably on the island’s south (lee) side. The inferred overwash may have caused restriction directly by washing sand into former inlets, or indirectly by reducing the tidal prism or supplying sand to post-overwash currents and waves. The overwash happened after A.D. 1650 if coeval with radiocarbon-dated leaves in the mud cap, and it probably happened before human settlement in the last decades of the 1700s. A prior overwash event is implied by an inland set of breaches. Hypothetically, the overwash in 1650–1800 resulted from the Antilles tsunami of 1690, the transatlantic Lisbon tsunami of 1755, a local tsunami not previously documented, or a storm whose effects exceeded those of Hurricane Donna, which was probably at category 3 as its eye passed 15 km to Anegada’s south in 1960.The work was supported in part by the Nuclear Regulatory Commission under its project N6480, a
tsunami-hazard assessment for the eastern United States
CMR-determined scar volume: predictive for ventricular tachycardias?
The interesting data reported by Bernhardt et al. strengthen the diagnostic benefit of CMR in patients with ischemic cardiomyopathy. Consequently, the presence, location and size of the CMR-determined scar tissue may be used for better risk stratification in patients with ischemic cardiomyopathy eligible for ICD therapy
Life Cycle Assessment of tandem LSC-Si devices
Given the increasing interest in tandem silicon-based solar cells and the recent advances in luminescent solar concentrators, the luminescent solar concentrators/silicon tandem structure has been proposed as an option for a four-terminal tandem structure. As part of the evaluation of a new type of solar cell, it is important to conduct a Life Cycle Assessment to effectively guide research efforts towards cell designs with minimum environmental impacts. Here, we carry out a process-based Life Cycle Assessment to assess global warming, human toxicity (carcinogenic and non-carcinogenic), freshwater eutrophication and ecotoxicity and abiotic depletion potential impacts associated with three luminescent solar concentrators/silicon tandem cell structures, considering a bottom layer as being a passivated emitter rear contact silicon solar cell. The results are based on experimental parameters and show that the increase in the performance of the cells and modules using the studied tandem structure can produce lower environmental effects than the passivated emitter rear contact technology (single-junction) for the impact categories studied. These results encourage the studies on cell and module performance improvements using such tandem luminescent solar concentrators/silicon structures
Impact of scheduling free goods on the throughput performance of a manufacturing operation
THE EFFECTS OF INTERRATER AND SELF-OTHER AGREEMENT ON PERFORMANCE IMPROVEMENT FOLLOWING UPWARD FEEDBACK
SELF- VERSUS OTHERS' RATINGS AS PREDICTORS OF ASSESSMENT CENTER RATINGS: VALIDATION EVIDENCE FOR 360-DEGREE FEEDBACK PROGRAMS
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