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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,279 records · Page 71
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Capacitive deionization charge transfer from one capacitor simultaneously to multiple capacitors

An energy transfer system is disclosed which has a controller, a first capacitor acting as a first electrode, a second capacitor acting as a second electrode, a first inductor for storing energy received from the first capacitor, and transferring the stored energy to the second capacitor, and a first plurality of electronic switches. The first plurality of electronic switches may be controlled by the controller to control a transfer of energy from the first capacitor to the first inductor, and from the first inductor to the first capacitor. An additional energy transfer subsystem may be included which has a second inductor for receiving energy from the first capacitor while the first inductor is transferring the stored energy to the second capacitor.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

On Performance Prediction of Big Data Transfer in High-performance Networks

Big data generated by large-scale scientific and industrial applications need to be transferred between different geographical locations for remote storage, processing, and analysis. High-speed dedicated connections provisioned in High-performance Networks (HPNs) are increasingly utilized to carry out such big data transfer. HPN management highly relies on an important capability of performance (mainly throughput) prediction to reserve sufficient bandwidth and meanwhile avoid over-provisioning that may result in unnecessary resource waste. This capability is critical to improving the resource (mainly bandwidth) utilization of dedicated connections and meeting various user requests for data transfer. Conventional methods conduct performance prediction by fitting prior observed transfer history with predefined loss functions, without considering unobservable latent factors such as competing loads on end hosts. Such latent factors also have a significant impact on the application-level data transfer performance, which may result in an inaccurate prediction model. In this paper, we first investigate the impact of latent factors and propose a clustering-based method to eliminate their negative impact on performance prediction. We then develop a robust machine learning-based performance predictor by: i) incorporating the proposed latent factor elimination method into data preprocessing, and ii) adopting a customized domain guided loss function. Extensive experimental results show that our predictor achieves significantly higher prediction accuracy than several other state-of-the-art methods.

Liu, Wuji↗
DOE OSTI2020

Heat transfer unit for prefabricated vessel

Vessel assemblies, heat transfer units for prefabricated vessels, and methods for heat transfer prefabricated vessel are provided. A heat transfer unit includes a central rod, and a plurality of peripheral rods surrounding the central rod and connected to the central rod. The plurality of peripheral rods are movable between a first collapsed position and a second bowed position, wherein in the second bowed position a midpoint of each of the plurality of peripheral rods is spaced from the central rod relative to in the first position. The heat transfer unit further includes a heat transfer element connected to one of the plurality of peripheral rods.

Tamburello, David A.↗
DOE OSTI2021

Capacitive wireless power transfer circuit and related techniques

Capacitive wireless power transfer systems are provided. In one embodiment, for example, the system comprises two pair of coupled conducting plates; a first matching network coupled to the first pair of conducting plates; and a second matching network coupled to the second pair of conducting plates. At least one of the first and second matching networks comprises an inductor having inductance value selected based on at least one parasitic capacitance value of the capacitive wireless power transfer system. In another embodiment, a method of designing a capacitive wireless power transfer system is provided comprising determining a parasitic capacitance value of a capacitive wireless power transfer system and determining an inductance value of an inductor of at least one of the first and second matching network having a value selected based on at least one parasitic capacitance value of the capacitive wireless power transfer system.

Afridi, Khurram K.↗
DOE OSTI2022

Impact of Variable Gas Mixtures on Bubble Size Distribution and Mass Transfer in Gas Fermentation Reactors

Gas fermentation has emerged as a promising new technology for the generation of fuels and chemicals from mixtures of greenhouse and energy rich gas streams (CO2/CH4/H2/CO) via microbial bioreaction. Example pathways include biomethanation (CO2/H2 to CH4), biogas upgrading, CO fermentation and wet-waste conversion. Effective Gas-liquid mass-transfer is an important physical phenomenon that determines the design and scale-up of these systems. There is currently a knowledge-gap regarding bubble-size distributions when using a mixture of gases with vastly different properties, which can have a significant impact on overall mass-transfer. For example, hydrogen bubbles are more buoyant compared to other relatively heavier gases (CO2/CH4/CO), resulting in a large distribution of residence times and bubble sizes. This work therefore develops a deeper understanding of bubble dynamics and interphase mass transfer in such heterogenous gas mixtures through well-resolved computational models. We use a detailed multiphase computational-fluid-dynamics (CFD) model to study the impact of gas-mixtures on overall mass-transfer in bubble column and air-lift reactors. The CFD tool previously developed by the authors (1) for simulating aerobic fermentation reactors at scale is used in this study. The Reynolds-averaged mass, momentum, energy, and species transport equations are solved for interpenetrating gas and liquid phase in this model. We use a population balance-based bubble-size-distribution model that is validated against small-scale experiments in our solver. Results pertaining to multiple simulations of gas-fermentation reactors are presented where gas mixtures with varying compositions of CO2/CH4/CO/H2 are imposed at the sparger boundaries. The spatio-temporal variations in bubble-size distribution and mass transfer coefficient is analyzed for varying superficial velocities and gas-compositions for varying sizes of bubble-column and airlift reactors.

BIOMASS FUELS,MATHEMATICS AND COMPUTING↗
DOE OSTI2012

Demonstration of Mixing and Transferring Settling Cohesive Slurry Simulants in the AY-102 Tank - 12323

In support of Hanford's feed delivery of high level waste (HLW) to the Waste Treatment and Immobilization Plant (WTP), pilot-scale testing and demonstrations with simulants containing cohesive particles were performed as a joint collaboration between Savannah River National Laboratory (SRNL) and the Pacific Northwest National Laboratory (PNNL) staff. The objective of the demonstrations was to determine the impact that cohesive particle interactions in the simulants, and the resulting non- Newtonian rheology, have on tank mixing and batch transfer of large and dense seed particles. The work addressed the impacts cohesive simulants have on mixing and batch transfer performance in a pilot-scale system. Kaolin slurries with a range of wt% concentrations to vary the Bingham yield stress were used in all the non-Newtonian simulants. To study the effects of just increasing the liquid viscosity (no yield stress) on mixing and batch transfers, a glycerol/water mixture was used. Stainless steel 100 micron particles were used as seed particles due to their density and their contrasting color to the kaolin and glycerol. Testing results show that water always transfers less seed particles, and is conservative when compared to fluids with a higher yield stress and/or higher viscosity at the same mixing/transfer parameters. The impact of non-Newtonian fluid properties depends on the magnitude of the yield stress. A higher yield stress in the carrier fluid resulted in more seed particles being transferred to the RTs. A dimensional analysis highlighting the role of a yield stress (due to cohesive particle interactions) defined four regions of behavior and indicates how the results obtained in this study can be applied to the full-scale mixing behavior of a high level waste tank. The analysis indicates that the regions of behavior for full-scale mixing have been adequately represented by the current small-scale tests. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

Setting an optimal procedure for transferring intermediate radioactive effluents: contribution of laboratory experiments - 15234

The INB35 nuclear facility at the CEA Saclay center is in charge of collecting and treating radioactive effluents generated from site's research activities. The first step of the process consists of an evaporation. The concentrate is an IL radioactive suspension with high salt concentration and suspended matter content. Until the 1990's, the resulting effluents were bitumen coated and since 2012 they have been cemented. During the 1990's, concentrates were stored in 7 tanks, named MA50X with X from 1 to 7. With today's changes to safety regulations, the effluents must now be transferred before tank dismantling. According to the site records, the compositions of the liquid wastes MA501, MA502, MA503, MA504, MA506 and MA507 are similar. From 2013 to 2014, effluents contained in MA502, MA503, MA504 tanks have been transferred. Several difficulties have been encountered: - The tanks were historically different, especially manhole tank access - Since the 1990's, effluent composition has changed due to water evaporation. The salt concentration has increased and insoluble elements have formed a deposit in the bottom of the tanks resulting in high composition heterogeneity - In some tanks, a wall breeze-blade exists dividing the tank into two zones, which complicates the interventions. Major challenges have been met and will be described in the presentation. - To obtain an effluent which is as homogeneous as possible, the duration of mixing has been optimized. - To pump the liquid, it has been necessary to treat the effluent with nitric acid. This step has been optimized thanks to experiments in laboratory and hydrodynamic modelling. - A mobile workshop has been designed in order to perform the effluent transfer. It is set up directly above the tanks and can be moved from one tank to another on rails. Laboratory experiments have been carried out to characterize the suspension and sludge in order to understand its chemical behavior. - The treatment of the effluent has been studied in the laboratory and is now mastered. - The analytical strategy has been optimized. The close collaboration between the analytical laboratory and the dismantling project was a real advantage. Thanks to this, the duration of the last transfer on MA 504 was reduced by half, compared to the first operations. Transfer operations will be described and the differences and similarities between laboratory and in-situ observations will be pointed out. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Determination of Erosion/Corrosion Rates in Hanford Tank Farms Radioactive Waste Transfer System Pipelines - 16395

The twenty-eight double-shell underground radioactive waste storage tanks at the U.S. Department of Energy's Hanford Site near Richland, WA are interconnected by the Waste Transfer System network of buried steel encased pipelines and pipe jumpers in below-grade pits. The pipeline material is stainless steel or carbon steel in 51 mm to 152 mm (2 in. to 6 in.) sizes. The pipelines carry slurries ranging up to 20 volume percent solids and supernatants with less than one volume percent solids at velocities necessary to prevent settling. The pipelines, installed between 1976 and 2011, were originally intended to last until the 2028 completion of the double-shell tank storage mission. The mission has been subsequently extended. In 2010 the Tank Operating Contractor began a systematic evaluation of the Waste Transfer System pipeline conditions applying guidelines from API 579-1/ASME FFS-1 (2007), Fitness-For- Service. Between 2010 and 2014 Fitness-for-Service examinations of the Waste Transfer System pipeline materials, sizes, and components were completed. In parallel, waste throughput histories were prepared allowing side-by-side pipeline wall thinning rate comparisons between carbon and stainless steel, slurries and supernatants and throughput volumes. The work showed that for transfer volumes up to 6.1 E+05 m{sup 3} (161 million gallons), the highest throughput of any pipeline segment examined, there has been no detectable wall thinning in either stainless or carbon steel pipeline material regardless of waste fluid characteristics or throughput. The paper describes the field and laboratory evaluation methods used for the Fitness-for-Service examinations, the results of the examinations, and the data reduction methodologies used to support Hanford Waste Transfer System pipeline wall thinning conclusions. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2018

Extensive Aging and Evaluation of Nonmetallic Components in the Waste Transfer System at Hanford - 18371

Nonmetallic materials are used in the United States Department of Energy's Hanford Site Tank Farm waste transfer system. These materials include the inner primary hoses in the hose-in-hose transfer lines (HIHTLs), Garlock{sup R} gaskets, ethylene propylene diene monomer (EPDM) O-rings, and other nonmetallic materials. These nonmetallic materials are exposed to β and γ radiation, caustic solutions as well as high temperature and pressure stressors. How the nonmetallic components react to each of these stressors individually has been well established. However, simultaneous exposure of these stressors has not been evaluated and is of great concern to Hanford Site engineers. FIU-ARC engineers worked closely with key Hanford HLW personnel to develop an experimental test plan that determines how these nonmetallic components react to various simultaneous stressor exposures. In this paper, data obtained from experimental testing of the hose-in-hose transfer lines, Garlock{sup R} gaskets and EPDM O-rings used in the Hanford tank farm waste transfer system under simultaneous stressor exposures is presented. The stressor exposure experiments consisted of combinations of simultaneous stressor exposure of caustic solution and elevated temperature stressors. Evaluation of materials that have been conditioned with the various stressors for duration of 6-months was conducted and compared with baseline unexposed materials. Evaluations included burst pressure tests of the EPDM hose-in-hose transfer lines, leak pressure tests of the EPDM O-rings and Garlock{sup R} gaskets, material tensile strength test of EPDM and Garlock{sup R} coupons. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) was conducted on aged and un-aged baseline coupons to determine if there was any change in the surface microstructure and to see how far the NaOH penetrated analysis is continuing. Conclusions from the 6-month testing indicates that the specimens did not see a significant in the pressure tests, but the material properties of both the EPDM and Garlock{sup R} coupons did see changes. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Preparing the FUSRAP Colonie Interim Storage Site for Transfer Back to the US Department of Energy Office of Legacy Management - 19215

The Formerly Utilized Sites Remedial Action Program (FUSRAP) Colonie Interim Storage Site was transferred from the US Department of Energy (US DOE) to the US Army Corps of Engineers (USACE) in 1997. The USACE initiated remediation efforts at the Site under FUSRAP. The Site was separated into three distinct operable units (OU) to more efficiently manage the remedial process: 1) Groundwater OU, 2) Main Site Soils OU, and 3) Vicinity Property OU. The USACE has completed remedial actions at each of these three OUs and has advanced the OU remedies at the Site to the long-term stewardship stage to be executed by the US DOE Office of Legacy Management (LM). The US DOE LM is the current real property owner of record of the Colonie Main Site. A summary of each OU and the activities needed to prepare for site transfer follows: OU 1 - USACE issued the Colonie Groundwater OU Record of Decision (ROD) (USACE 2010a) on April 9, 2010. The Groundwater ROD remedy is monitored natural attenuation (MNA) and long-term monitoring (LTM) of groundwater after source removal completion. Results of groundwater monitoring indicate reductions in concentrations of contaminants of concern (COC). Based on the marked progress to date, USACE has optimized the groundwater LTM program (USACE, 2014) by reducing the well network, sampling frequency, and analytical parameters, and by abandoning wells that are no longer needed. A Groundwater ROD Five-Year Review report was submitted to the New York State Department of Environmental Conservation (NYSDEC) for review in 2018. NYSDEC agreed that MNA is still an appropriate remedial method although it is progressing at a slower rate than predicted. OU 2 - From 1999 to 2007, USACE completed the large-scale removal of soil at the Main Site, which included the adjacent Town of Colonie Vicinity Property. Radioactively contaminated soil along with accessible metals-contaminated soil and soil containing volatile organic compounds (VOC) were removed during this effort. A total of 103,402 cubic meters (m{sup 3}) of soil was excavated and disposed offsite. On March 26, 2015, USACE signed the Main Site Soils OU ROD (USACE, 2015a). The ROD remedy included provisions for Land Use Controls (LUC) consisting of institutional controls (IC) through an Environmental Easement for management of three small and discrete inaccessible locations within three of the 27 Final Status Survey units of the Main Site. The Environmental Easement provides a means of protection based on both current and future land use by placing restrictions on soil excavation and reuse. The easement and a supporting Site Management Plan (SMP) will be finalized by LM in coordination with NYSDEC. OU 3 - the Vicinity Property OU ROD was signed on 20 September 2017. This ROD declared No Action (NA) for dust and No Further Action (NFA) for soil and other media for the Vicinity Properties. Prior to the ROD, USACE performed dust sampling and other characterization activities at representative commercial and residential Vicinity Property locations. These efforts were reported in the Colonie FUSRAP Site Vicinity Property Operable Unit Remedial Investigation Summary Report (USACE, 2016). A Site Closeout Report (SCOR) was issued to NYSDEC and approved in 2018. The approval of this report starts the transfer process back to the LM. Ongoing and future transfer activities include records retention and management, preparation and filing of real estate records, physical site management (fencing, landscape maintenance, well abandonment) and coordination with state regulators and LM staff. This presentation is intended to make all stakeholders aware of the necessary steps for site transfer from the USACE back to the LM. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

A fully integrated 3D CFD model of the flow and heat transfer in a packed bed reactor - 18578

The physical phenomena associated with the modes of heat transfer within a packed pebble bed can be modelled by explicitly solving the associated partial differential equations using a finite volume method approach. Convection from the spheres to coolant, conduction inside and between spheres as well as radiation between various components of a packed bed reactor are the main modes of heat transfer, with several lesser, albeit contributing, phenomena also present. Advances both in software and computing power allow for a larger portion of a packed bed to be modeled with greater accuracy by integrating all applicable physics models in one simulation. A representative unstructured packed bed of uniform spheres was generated with a discrete element method (DEM) and the flow domain modelled using the CFD software package Star-CCM+, taking into account all primary modes of heat transfer as well as a user-specified approach to take secondary effects into account. Effects in the bulk, near-wall and wall-contact regions were investigated. By using such a fully integrated explicit model, a deeper understanding can be can be gained into the role of the underlying phenomena and their respective contributions to the overall heat transfer process. Fuel spheres were modeled explicitly with the conduction between spheres, bed and reflectors being prescribed by contact heat transfer theory as a function of temperature and compressive forces within the bed. The effective thermal conductivity (k{sub eff}), flow pressure drop, as well as temperature distributions in the spheres and coolant were calculated and compared with experimental results from published literature. Good agreement was found with experimental results and the significant contribution of radiation as well as inter-pebble conduction to the effective thermal conductivity could be observed from the results. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2019

Challenges of future high power wireless power transfer for light-duty electric vehicles----technology and risk management

Wireless power transfer is a state-of-the-art technology with the advantage of convenience and flexibility, as well as the capability of enabling fully automated charging. With power transfer levels increasing beyond 100 kW, many technical and risk management challenges emerge. Here, instead of focusing on the progress review of wireless power transfer technology, this paper discusses the future challenges and risks for high power wireless charging for light-duty electric vehicles. Aiming at 200 kW or higher wireless power transfer, we discuss technology and risk management challenges in the area of electromagnetic safety, resonant frequency determination, and cybersecurity risks in detail. As potential solutions to overcome these challenges, the latest technologies with an emphasis on advanced shielding solutions and recent progress on SiC converters from both industrial and academic institutions are reviewed, and some perspectives and propositions are provided.

25 ENERGY STORAGE↗
DOE OSTI2020

Single Entity Electrochemistry in Nanopore Electrode Arrays: Ion Transport Meets Electron Transfer in Confined Geometries

Electrochemical measurements conducted in confined volumes provide a powerful and direct means to address scientific questions at the nexus of nanoscience, biotechnology, and chemical analysis. How are electron transfer and ion transport coupled in confined volumes and how does understanding them require moving beyond macroscopic theories? Also, how do these coupled processes impact electrochemical detection and processing? We address these questions by studying a special type of confined-volume architecture, the nanopore electrode array, or NEA, which is designed to be commensurate in size with physical scaling lengths, such as the Debye length, a concordance that offers performance characteristics not available in larger scale structures. The experiments described here depend critically on carefully constructed nanoscale architectures that can usefully control molecular transport and electrochemical reactivity. We begin by considering the experimental constraints that guide the design and fabrication of zero-dimensional nanopore arrays with multiple embedded electrodes. These zero-dimensional structures are nearly ideal for exploring how permselectivity and unscreened ion migration can be combined to amplify signals and improve selectivity by enabling highly efficient redox cycling. Our studies also highlight the benefits of arrays, in that molecules escaping from a single nanopore are efficiently captured by neighboring pores and returned to the population of active redox species being measured, benefits that arise from coupling ion accumulation and migration. These tools for manipulating redox species are well-positioned to explore single molecule and single particle electron transfer events through spectroelectrochemistry, studies which are enabled by the electrochemical zero-mode waveguide (ZMW), a special hybrid nanophotonic/nanoelectronic architecture in which the lower ring electrode of an NEA nanopore functions both as a working electrode to initiate electron transfer reactions and as the optical cladding layer of a ZMW. Furthermore, while the work described here is largely exploratory and fundamental, we believe that the development of NEAs will enable important applications that emerge directly from the unique coupled transport and electron-transfer capabilities of NEAs, including in situ molecular separation and detection with external stimuli, redox-based electrochemical rectification in individually encapsulated nanopores, and coupled sorters and analyzers for nanoparticles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Bridge-Mediated Metal-to-Metal Electron and Hole Transfer in a Supermolecular Dinuclear Complex: A Computational Study Using Quantum Electron–Nuclear Dynamics

Bimetallic electron donor–acceptor complexes can facilitate electron and energy transfer with excellent structural control through synthetic design. In this work, we investigate the photochemical dynamics in a Ru–Cu bimetallic complex after photoexcitation of the Ru-centered charge transfer state. The physical underpinnings of the metal-to-metal directional charge transfer process are unraveled via analyses of the quantum electronic dynamics and electron–nuclear trajectories. Here, the effects of molecular vibrations in the photoexcited state on the charge transfer processes are also analyzed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Chirped Laser Pulse Control of Vibronic Wavepackets and Energy Transfer in Phycocyanin 645

Photosynthetic organisms use light-harvesting complexes to increase the spectrum of light that they absorb from solar photons. Recent ultrafast spectroscopic studies have revealed that efficient (sub-ps) energy transfer is mediated by vibronic coherence in the phycobiliprotein phycocyanin 645 (PC645). Here, we report studies that employ broadband pump–probe spectroscopy with linearly chirped excitation pulses to further investigate the relationship between vibronic state preparation and energy transfer dynamics in PC645. Negatively chirped pulse excitation is found to enhance wavepackets of a high-frequency mode (1580 cm –1 ) and increase the rate of downhill energy transfer, while on the other hand, positively chirped pulses suppress these oscillatory features and decrease this rate. Model calculations incorporating the influence of the chirped pump pulse are used to understand its effect on initial state preparation. Furthermore, these results provide mechanistic insight into how the overall nonequilibrium rate of energy transfer is influenced by initial state preparation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Base-Free Catalytic Transfer Hydrogenation of Alkyl Formates and Organic Esters at Mild Temperature

The pincer-ligated ruthenium complex ( iPr PN H P)Ru(CO)H 2 ( iPr PN H P = ( i Pr 2 PC 2 H 4 ) 2 NH) is an active catalyst for the transfer hydrogenation of alkyl formates (HCO 2 R) and organic esters (RCO 2 R′) to the corresponding alcohols under base-free reaction conditions at mild temperatures. Specifically, a range of alkyl formate esters were reduced to MeOH and the corresponding alcohols in high yields using ( iPr PN H P)Ru(CO)H 2 as the catalyst and isopropanol ( i PrOH) as the hydrogen donor at 30 °C. The first step in the process is the metal-catalyzed transesterification of the alkyl formate with i PrOH to generate isopropyl formate, which is then reduced. The use of i PrOH as the hydrogen donor is crucial. ( iPr PN H P)Ru(CO)H 2 can also catalyze the transfer hydrogenation of a broad range of organic esters, including cyclic, acyclic, heteroatom-substituted, and long-chain bio-derived esters, to the corresponding alcohols in good yields using ethanol (EtOH) as the hydrogen donor at 55 °C. Computational studies were used to elucidate the proposed pathway for alkyl formate reduction and the underlying reasons why i PrOH is the most effective hydrogen donor for alkyl formate reduction, while EtOH is optimal for organic ester reduction. Overall, this work describes a highly active catalyst for alkyl formate and organic ester transfer hydrogenation and provides mechanistic insight into the factors responsible for the strong catalytic performance. Finally, these findings will be valuable for designing catalysts for both transfer hydrogenation and related reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Highly Efficient Plasmon Induced Hot-Electron Transfer at Ag/TiO 2 Interface

Plasmon induced hot carrier transfer is a promising novel approach for solar energy conversion, but its practical application is often hindered by its low efficiency. This work demonstrates an unprecedented quantum efficiency of plasmonic hot-electron transfer of up to 53 ± 2% from 1.7 nm silver nanoparticles to anatase nanoporous TiOsub>2 films at 400 nm excitation. This efficient hot-electron transfer consists of contributions of both hot electrons generated by plasmon decay through exciting Ag intraband transitions and Ag-to-TiO 2 interfacial charge-transfer transitions. The efficiencies of both pathways increase at smaller Ag particle sizes from 5.9 to 1.7 nm, suggesting that decreasing particle sizes is a promising way toward efficient plasmonic hot-carrier extraction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Wavelength-Dependent Energy and Charge Transfer in MOF: A Step toward Artificial Porous Light-Harvesting System

Chromophore assemblies within well-defined porous coordination polymers, such as metal–organic frameworks (MOFs), can emulate the functionality of the antenna rings of chlorophylls in light-harvesting complexes (LHCs). The chemical, electronic, and structural diversities define MOFs as a promising platform where photogenerated excitons can be displaced to redox catalysts similar to the reaction center of the LHC. The precise positioning of the pigments and complementary redox units enables us to understand the charge/energy-transfer process within these crystalline solid compositions. In this study, we postsynthetically anchored tetraphenylporphyrinato zinc(II) (TPPZn)-derived complementary pigment within the 1D pores of 1,3,6,8-tetrakis(p-benzoicacid)pyrene (H4TBAPy)-derived NU-1000 MOF to form a high-density donor–acceptor system. The ground- and excited-state redox potentials of the donor and acceptor were chosen to facilitate an energy transfer (EnT) from the excited MOF (i.e., NU-1000*) to TPPZn and a charge transfer (CT) from excited porphyrin (i.e., TPPZn*). Thus, the processes depend on the excitation wavelength. The energy transfer process was spectroscopically probed by excitation–emission mapping: MOF emission was completely quenched at 460 nm, where the pyrene-centered emission was expected. Instead, the excited MOF efficiently transfers the energy to manifest a TPPZn-centered emission at 670 nm (k EnT ≈ 4.7 × 10 11 s–1). The excited TPPZn pigment, with a neighboring TBAPy linker, forms an artificial “special-pair”-like system driving the charge-separation process (k CT = 1.2 × 10 10 s –1 ). The findings demonstrate a synthetic MOF-based artificial LHC system where their well-defined structure will open up new possibilities as the separated charge can hop along the 1D pore channel for further mechanistic understanding and future developments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗