Engineering topics
Atwater, Harry A.
Publications and source records attributed to Atwater, Harry A..
Measurement of ion transport properties in ion exchange membranes for photoelectrochemical water splitting
Photoelectrochemical (PEC) water-splitting systems have the unique ability to produce renewable hydrogen directly from sunlight, independent of the electrical grid. These systems are therefore appealing technological options for resilient long-term energy storage. Ion selective membranes, such as monopolar and bipolar membranes, are a vital component of PEC water-splitting systems. These membranes allow for ionic conduction between the cathode and anode chambers, separation of products, and improved catalyst environments for reactions. In order to measure key properties and to study the performance of these ion exchange membranes, it is imperative to develop a robust testing protocol that can be used across the field. This paper introduces two standard electrochemical cells designed to directly measure ion transport properties in monopolar and bipolar membranes. The first electrochemical cell uses commercially available Pt disk electrodes to preform electrochemical impedance spectroscopy (EIS) and reliably measure through-plane conductivity of monopolar membranes. The second electrochemical cell uses four-point measurements with Luggin capillaries and a series of membrane configurations to perform current density-voltage and Faradaic efficiency (FE) measurements for water dissociation (WD) reactions on bipolar membranes. The cell designs and techniques laid out below allow for accurate measurement of ion transport parameters in ion exchange membranes, direct comparison of membranes being developed across the field, and in turn, greater advancements in ion exchange membranes and PEC water-splitting systems.
Integrated Solar-Driven Device with a Front Surface Semitransparent Catalysts for Unassisted CO 2 Reduction
Monolithic integrated photovoltaic-driven electrochemical (PV-EC) artificial photosynthesis is reported for unassisted CO 2 reduction. The PV-EC structures employ triple junction photoelectrodes with a front mounted semitransparent catalyst layer as a photocathode. The catalyst layer is comprised of an array of microscale triangular metallic prisms that redirect incoming light toward open areas of the photoelectrode to reduce shadow losses. Full wave electromagnetic simulations of the prism array (PA) structure guide optimization of geometries and length scales. An integrated device is constructed with Ag catalyst prisms covering 35% of the surface area. The experimental device has close to 80% of the transmittance with a catalytic surface area equivalent 144% of the glass substrate area. Experimentally this photocathode demonstrates a direct solar-to-CO conversion efficiency of 5.9% with 50 h stability. Selective electrodeposition of Cu catalysts onto the surface of the Ag triangular prisms allows CO2 conversion to higher value products enabling demonstration of a solar-to-C 2+ product efficiency of 3.1%. This design featuring structures that have a semitransparent catalyst layer on a PV-EC cell is a general solution to light loss by shadowing for front surface mounted metal catalysts, and opens a route for the development of artificial photosynthesis based on this scalable design approach.
Role of Atomic Structure on Exciton Dynamics and Photoluminescence in NIR Emissive InAs/InP/ZnSe Quantum Dots
Not Available
Luminescent solar concentrators and related methods of manufacturing
Luminescent solar concentrators in accordance with various embodiments of the invention can be designed to minimize photon thermalization losses and incomplete light trapping using various components and techniques. Cadmium selenide core, cadmium sulfide shell (CdSe/CdS) quantum dot (“QD”) technology can be implemented in such devices to allow for near-unity QDs and sufficiently large Stokes shifts. Many embodiments of the invention include a luminescent solar concentrator that incorporates CdSe/CdS quantum dot luminophores. In further embodiments, anisotropic luminophore emission can be implemented through metasurface/plasmonic antenna coupling. In several embodiments, red-shifted luminophores are implemented. Additionally, top and bottom spectrally-selective filters, such as but not limited to selectively-reflective metasurface mirrors and polymeric stack filters, can be implemented to enhance the photon collection efficiency. In some embodiments, luminescent solar concentrator component is optically connected in tandem with a planar Si subcell, forming a micro-optical tandem luminescent solar concentrator.
A hybrid coupler for directing quantum light emission with high radiative Purcell enhancement to a dielectric metasurface lens
Quantum photonic technologies such as quantum sensing, metrology, and simulation could be transformatively enabled by the availability of integrated single photon sources with high radiative rates and photon collection efficiencies. We address these challenges for quantum emitters formed from color center defect sites such as those in hexagonal boron nitride, which are promising candidates as single photon sources due to their bright, stable, polarized, and room temperature emission. We report design of a nanophotonic coupler from color center quantum emitters to a dielectric metasurface lens. The coupler is comprised of a hybrid plasmonic–dielectric resonator that achieves a large radiative Purcell enhancement and partial control of far-field radiation. We report radiative Purcell factors up to 285 and photon collection efficiencies up to 89% for a lossless metasurface, applying a continuous hyperboloidal phase-front. Our hybrid plasmonic–dielectric coupler interfacing two nanophotonic elements is a compound optical element, analogous to those found in microscope objective lenses, which combine multiple optical functions into a single component for improved performance.
Broadband electro-optic polarization conversion with atomically thin black phosphorus
Metasurfaces tune polarization In photonic systems, the polarization state of light is typically manipulated with bulky components based on dielectrics and liquid crystals. Active metasurfaces now provide the possibility of shrinking the size of these components to the nanoscale. Biswas et al . demonstrate an active nanophotonic structure capable of versatile electro-optic polarization conversion. Using trilayer black phosphorus sandwiched between electrical gates forming a cavity, they show that the polarization state of light across telecommunication wavelengths can be electrically switched. Such control can be useful for a number of applications in communications, imaging, and beam steering where the wavefront of the propagating light can be actively manipulated. —ISO
Hydrogen from Sunlight and Water: A Side-by-Side Comparison between Photoelectrochemical and Solar Thermochemical Water-Splitting
Photoelectrochemical (PEC) and solar thermochemical (STCH) water-splitting represent two promising pathways for direct solar hydrogen generation. PEC water-splitting integrates multiple functional materials and utilizes energetic electrons and holes generated from sunlight to produce hydrogen and oxygen in two half-reactions, while STCH water-splitting couples a series of consecutive chemical reactions and uses absorbed heat from sunlight to generate hydrogen and oxygen in two full reactions. In this Focus Review, the basic operating principles, sunlight utilization, device architecture, reactor design, instantaneous and annually averaged solar-to-hydrogen (STH) conversion efficiency, and the operating conditions and constraints of both pathways are compared. A side-by-side comparison addresses some common sources of confusion and misinterpretation, especially in the evaluation of STH conversion efficiencies, and reveals distinct features and challenges in both PEC and STCH technologies. Furthermore, this Focus Review also addresses materials and device challenges in PEC and STCH for cost-competitive hydrogen generation.