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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 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Three-dimensional MoO3 nanoflowers assembled with nanosheets for rhodamine B degradation under visible light

Highlights: • The orthorhombic three-dimensional MoO{sub 3} nanoflowers were synthesized by the modified hydrothermal method. • Using different amount of HCl to transfer from the h-MoO{sub 3} to the α-MoO{sub 3} was well discussed. • Better pore sizes and surface areas of the three-dimensional MoO{sub 3} nanoflowers accelerate the photodegradation process of RhB. • The three-dimensional MoO{sub 3} nanoflowers showed the photocatalytic activity (91.57%). • This methodology should be useful for preparing other nanostructured catalysts. - Abstract: Three-dimensional hierarchical nanoflowers self-assembled with the orthorhombic molybdenum oxide (α-MoO{sub 3}) nanoflowers were synthesized by the modified hydrothermal method. The structure characterizations of the three-dimensional α-MoO{sub 3} nanoflowers were carried out by scanning electron microscope (SEM), Energy Disperse Spectroscopy (EDS), X-ray diffraction (XRD) and nitrogen adsorption-desorption measurement. Moreover, the three-dimensional α-MoO{sub 3} nanoflowers as photocatalyst exhibited enhanced photocatalytic activity towards photodegradation of Rhodamine B (RhB) under xenon (Xe) lamp irradiation. The results of SEM, EDS, XRD and nitrogen adsorption-desorption measurement showed the three-dimensional α-MoO{sub 3} nanoflowers have a better morphology, pore size (7.99 nm) and surface areas (50.788 m{sup 2} g{sup −1}) than hexagonal MoO{sub 3} (h-MoO{sub 3}) nanosheets, photocatalytic activity studies confirmed that the three-dimensional α-MoO{sub 3} nanoflowers photocatalyst exhibits a high visible-light-driven activity for photodegradation of RhB solution of 91.57% within 160 min under Xe lamp irradiation. A mechanism was also proposed for the degradation of RhB by three-dimensional α-MoO{sub 3} nanoflowers.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

UV–Visible reflectance of common light reflectors and their degradation after an ionization dose up to 100 Mrad

We report light reflectors are widely used to enhance scintillation light collection. Their enhancement level depends on the reflector’s reflectance at the scintillator’s emission wavelength. We report UV–Visible reflectance spectra, relative to BaSO 4 , for several common reflectors. Also reported is their radiation hardness against an ionization dose up to 100 Mrad. The results of this investigation provide a reference for applications of these reflectors in a severe radiation environment.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Pu(IV) quantification via visible–near-infrared absorption spectroscopy: tackling interferences using D-optimal design and partial least squares

Here, this study presents a novel analytical approach for quantifying Pu(IV) in glove box environments using fiber-optic-based visible–near-infrared absorption spectroscopy in combination with partial least squares regression (PLSR) and design of experiments. The method addresses significant challenges posed by overlapping spectral features arising from Nd(III), which is a common fission product impurity, and the speciation variability of Pu(IV) nitrato complexes in HNO 3 concentrations ranging from 2.5 to 11 M. A curated training set consisting of data from 20 samples was developed via D-optimal design to enable robust PLSR model calibration for Pu(IV) using the near-infrared band near 1050 nm. The training set was acquired from samples in cuvettes with a 1-cm path length and was used to build the PLSR model. The robustness of the model was validated with data collected using a dip probe with a 1-cm path length and varying Pu(IV) concentrations. The strong performance of the model indicates good model transfer from cuvette to dip probe and highlights the potential for in situ measurements and online monitoring of reactions in a crystallization reactor vessel. The results demonstrate that this combined spectroscopic and chemometric approach can accurately and simultaneously quantify Pu(IV) and HNO 3 , thereby offering a promising tool for real-time monitoring in process environments.

Actinide↗
DOE OSTI2025

Chemometrics and visible diffuse reflectance spectroscopy to classify plutonium dioxide

Diffuse reflectance (DR) spectra in the Vis-NIR (∼380–1050 nm) region were acquired for a series of PuO 2 samples with a spot size of about 10 × 10 μm. Two batches of six PuO 2 samples, synthesized approximately 7.5 months apart, were prepared using both Pu(III) and Pu(IV) oxalate precursors at three distinct calcination temperatures (450, 650, and 950 °C). This yielded a total of 12 PuO 2 samples and 433 DR spectra. The DR spectrum of PuO 2 contained numerous peaks in the visible region, and characteristic features were identified with respect to calcination temperature and chemistry. A distinct peak multiplet near 615 nm was observed for samples prepared at low calcination temperatures, and a peak near 660 nm was observed for higher calcination temperatures. A multivariate classification strategy based on principal component analysis (PCA) was developed to distinguish PuO 2 calcination temperatures of 450, 650, and 950 °C with 100 % accuracy. Classification results also indicate the potential to distinguish chemical processing history (i.e., Pu(III) or Pu(IV)) based on the spectra with 72 % accuracy based on k-nearest neighbors applied to the PCA scores. Partial least squares discriminant analysis was used to identify variation among batches with 88 % accuracy and found that peaks near 669, 681, 811, and 970 nm were the most useful for predicting the batch identity. Here, this work demonstrates how micro-diffuse reflectance spectroscopy and chemometrics can be used to classify PuO 2 processing history based on Vis-NIR spectral features. Combining the chemometric approach with mapping sequences could provide a rapid, nondestructive approach to classify Pu oxide materials for environmental, forensics, and nonproliferation applications.

Actinide↗
DOE OSTI2022

Revealing aggregation of non-fullerene acceptors in intermixed phase by ultraviolet-visible absorption spectroscopy

Non-fullerene acceptor (NFA) aggregation is crucial in determining bulk-heterojunction (BHJ) organic photovoltaic (OPV) performance. However, it is still a big challenge to characterize the nanostructure of NFAs in the disordered donor-acceptor intermixed phase. Here, we demonstrate a method to characterize NFA aggregation and composition in the intermixed phase by measuring NFA concentration-dependent ultraviolet-visible (UV-vis) absorption spectroscopy of BHJ films. In various polymer:NFA films, an absorption shift as a function of increasing molecular concentration (ASIMC) phenomenon is observed, and different NFA aggregation behaviors can be distinguished. The ASIMC method was then applied to study the influence of processing conditions on the NFA concentration in the intermixed phase of devices to establish a correlation with device efficiency. The current work provides a feasible tool to study the nanostructure of NFAs in the complex polymer matrix and to understand the variations in the NFA concentration in the intermixed phase under non-equilibrium conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Optimising the processing and storage of visibilities using lossy compression

The next-generation radio astronomy instruments are providing a massive increase in sensitivity and coverage, largely through increasing the number of stations in the array and the frequency span sampled. The two primary problems encountered when processing the resultant avalanche of data are the need for abundant storage and the constraints imposed by I/O, as I/O bandwidths drop significantly on cold storage. An example of this is the data deluge expected from the SKA Telescopes of more than 60 PB per day, all to be stored on the buffer filesystem. While compressing the data is an obvious solution, the impacts on the final data products are hard to predict. In this paper, we chose an error-controlled compressor – MGARD – and applied it to simulated SKA-Mid and real pathfinder visibility data, in noise-free and noise-dominated regimes. As the data have an implicit error level in the system temperature, using an error bound in compression provides a natural metric for compression. MGARD ensures the compression incurred errors adhere to the user-prescribed tolerance. To measure the degradation of images reconstructed using the lossy compressed data, we proposed a list of diagnostic measures, exploring the trade-off between these error bounds and the corresponding compression ratios, as well as the impact on science quality derived from the lossy compressed data products through a series of experiments. We studied the global and local impacts on the output images for continuum and spectral line examples. We found relative error bounds of as much as 10%, which provide compression ratios of about 20, have a limited impact on the continuum imaging as the increased noise is less than the image RMS, whereas a 1% error bound (compression ratio of 8) introduces an increase in noise of about an order of magnitude less than the image RMS. For extremely sensitive observations and for very precious data, we would recommend a 0.1% error bound with compression ratios of about 4. These have noise impacts two orders of magnitude less than the image RMS levels. At these levels, the limits are due to instabilities in the deconvolution methods. We compared the results to the alternative compression tool DYSCO, in both the impacts on the images and in the relative flexibility. MGARD provides better compression for similar error bounds and has a host of potentially powerful additional features.

Techniques: interferometric↗
DOE OSTI2015

When will low-contrast features be visible in a STEM X-ray spectrum image?

When will a small or low-contrast feature, such as an embedded second-phase particle, be visible in a scanning transmission electron microscopy (STEM) X-ray map? This work illustrates a computationally inexpensive method to simulate X-ray maps and spectrum images (SIs), based upon the equations of X-ray generation and detection. To particularize the general procedure, an example of nanostructured ferritic alloy (NFA) containing nm-sized Y 2 Ti 2 O 7 embedded precipitates in ferritic stainless steel matrix is chosen. The proposed model produces physically appearing simulated SI data sets, which can either be reduced to X-ray dot maps or analyzed via multivariate statistical analysis. Comparison to NFA X-ray maps acquired using three different STEM instruments match the generated simulations quite well, despite the large number of simplifying assumptions used. A figure of merit of electron dose multiplied by X-ray collection solid angle is proposed to compare feature detectability from one data set (simulated or experimental) to another. The proposed method can scope experiments that are feasible under specific analysis conditions on a given microscope. As a result, future applications, such as spallation proton–neutron irradiations, core-shell nanoparticles, or dopants in polycrystalline photovoltaic solar cells, are proposed.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Stabilization of Photocatalytically Active Uranyl Species in a Uranyl–Organic Framework for Heterogeneous Alkane Fluorination Driven by Visible Light

When photoactivated, the uranyl ion is a robust oxidant capable of abstracting hydrogen atoms from nonactivated C–H bonds. Yet, the highly reactive singly reduced [U V O 2 ] + intermediate is unstable with respect to disproportionation to the uranyl dication and insoluble tetravalent uranium phases, which limits the usage of uranyl ions as robust photocatalysts. Herein, we demonstrate that photoactivated uranyl ions can be stabilized by immobilizing and separating them spatially in a uranyl–organic framework heterogeneous catalyst, NU-1301. The visible-light-photoactivated uranyl ions in NU-1301 demonstrated longer-lived U(V) and radicals than those in homogeneous counterparts, as evidenced by X-ray photoelectron spectroscopy and time-dependent electron paramagnetic resonance, leading to higher turnovers and enhanced stability for the fluorination of nonactivated alkanes.

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

Direct Evidence of Visible Light-Induced Homolysis in Chlorobis(2,9-dimethyl-1,10-phenanthroline)copper(II)

Developments in the field of photoredox catalysis that leveraged the long-lived excited states of Ir(III) and Ru(II) photosensitizers to enable radical coupling processes paved the way for explorations of synthetic transformations that would otherwise remain unrealized. While first row transition metal photocatalysts have not been as extensively investigated, valuable synthetic transformations covering broad scopes of olefin functionalization have been recently reported featuring photoactivated chlorobis(phenanthroline) Cu(II) complexes. In this study, the photochemical processes underpinning the catalytic activity of [Cu(dmp) 2 Cl]Cl (dmp = 2,9-dimethyl-1,10-phenanthroline) were studied. The combined results from static spectroscopic measurements and conventional photochemistry, ultrafast transient absorption, and electron paramagnetic resonance spin trapping experiments strongly support blue light (λ ex = 427 or 470 nm)-induced Cu–Cl homolytic bond cleavage in [Cu(dmp) 2 Cl] + occurring in <100 fs. On the basis of electronic structure calculations, this bond-breaking photochemistry corresponds to the Cl → Cu(II) ligand-to-metal charge transfer transition, unmasking a Cu(I) species [Cu(dmp) 2 ] + and a Cl atom, thereby serving as a departure point for both Cu(I)- or Cu(II)-based photoredox transformations. No net photochemistry was observed through direct excitation of the ligand-field transitions in the red (λ ex = 785 or 800 nm), and all combined experiments indicated no evidence of Cu–Cl bond cleavage under these conditions. As a result, the underlying visible light-induced homolysis of a metal–ligand bond yielding a one-electron-reduced photosensitizer and a radical species may form the basis for novel transformations initiated by photoinduced homolysis featuring in situ-formed metal–substrate adducts utilizing first row transition metal complexes.

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

Visible-Light-Driven Triplet Sensitization of Polycyclic Aromatic Hydrocarbons Using Thionated Perinones

Metal-free chromophores that efficiently generate triplet excited states represent enticing alternatives with respect to transition metal-containing photosensitizers, such as those featuring metal-to-ligand charge transfer excited states. Yet, such molecular constructs have remained underexplored due to the unclear relationship(s) between molecular structure and efficient/rapid intersystem crossing. In this regard, we present a series of three thionated perinone chromophores serving as a newly conceived class of heavy metal-free triplet photosensitizers. We demonstrate that thionation of the lone C=O substituent in each highly fluorescent perinone imparts red-shifted absorbance bands that maintain intense extinction coefficients across the visible spectrum, as well as unusually efficient triplet excited state formation as inferred from the measured singlet O 2 quantum yields at 1270 nm (Φ Δ = 0.78–1.0). Electronic structure calculations revealed the emergence of a low energy S 1 (n → π*) excited state in the proximity of a slightly higher energy S 2 (π → π*) excited state. The distinct character in each of the two lowest-lying singlet state manifolds resulted in the energetic inversion of the corresponding triplet excited states due to differences in electron exchange interactions. Rapid S 1 → T 1 intersystem crossing was thereby facilitated in this manner through spin–orbit coupling as predicted by the El Sayed rules. The lifetimes of the resultant triplet excited states persisted into the microsecond time regime, as measured by transient absorbance spectroscopy, enabling effective bimolecular triplet sensitization of some common polycyclic aromatic hydrocarbons. The synthetically facile interchange of a single O atom to an S atom in the investigated perinones resulted in marked changes to their photophysical properties, namely, conversion of dominant singlet state fluorescence in the former to long-lived triplet excited states in the latter. The combined results suggest a general strategy for accessing long-lived triplet excited states in organic chromophores featuring a lone C=O moiety residing within its structure, valuable for the design of metal-free triplet photosensitizers.

14 SOLAR ENERGY↗
DOE OSTI2022

Colloidal Nanoribbons: From Infrared to Visible

Using the cation-exchange method, colloidal PbS nanoribbons are converted completely into CdS nanoribbons. This process expands the emission spectrum of the nanoribbons from infrared to visible. Here, the morphology of nanoribbons remains the same after cation exchange, but the crystal structure changes from rock salt to zincblende. CdS nanoribbons exhibit blue band-edge photoluminescence under ultraviolet-light excitation. Cathodoluminescence spectroscopy of the CdS nanoribbons shows multicolor (blue, green, and red) emissions. Further time-resolved photoluminescence spectroscopy studies show that the lifetime of the midgap states is more than 2 orders of magnitude longer than that of the band-edge states.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Gigahertz acoustic vibrations of elastically anisotropic Indium–tin-oxide nanorod arrays [Gigahertz modulation of the full visible spectrum via acoustic vibrations of elastically anisotropic Indium-tin-oxide nanorod arrays]

Active control of light is important for photonic integrated circuits, optical switches,. and telecommunications. Coupling light with acoustic vibrations in nanoscale optical resonators offers optical modulation capabilities with high bandwidth and Small footprint Instead of using noble metals, here we introduce indium tin-oxide nanorod arrays (ITO-NRAs) as the operating media;and demonstrate optical modulation covering the visible spectral range (from 360 to 700 nm), with similar to 20 GHz bandwidth through the excitation of coherent acoustic vibrations in ITO-NRAs. This broadband modulation results from the collective optical diffraction by the dielectric ITO-NRAs, and a high differential transmission modulation up to 10% is achieved through efficient near-infrared, on-plasmon-resonance pumping. By combining the frequency signatures Of the vibrational modes with finite-element simulations, we,further determine the anisotropic elastic constants for single-crystalline ITO, which are not known-for the bulk phase. Furthermore, this technique to determine elastic constants using Coherent acoustic vibrations of uniform nanostructures can be generalized to the study of other inorganic materials.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Nanocavity-Enhanced Giant Stimulated Raman Scattering in Si Nanowires in the Visible Light Region

Silicon photonics has been a very active area of research especially in the past two decades in order to meet the ever-increasing demand for more computational power and faster device speeds and their natural compatibility with complementary metal-oxide semiconductor. In order to develop Si as a useful photonics material, essential photonic components such as light sources, waveguides, wavelength convertors, modulators, and detectors need to be developed and integrated. However, due to the indirect electronic bandgap of Si, conventional light emission devices such as light-emitting diodes and lasers cannot be built. Therefore, there has been considerable interest in developing Si-based Raman lasers, which are nonlinear devices and require large stimulated Raman scattering (SRS) in an optical cavity. However, due to the low quantum yield of SRS in Si, Raman lasers have very large device footprints and high lasing threshold, making them unsuitable for faster, smaller, and energy-efficient devices. Here in this paper, we report strong SRS and extremely high Raman gain in Si nanowire optical cavities in the visible region with measured SRS threshold as low as 30 kW/cm 2 . At cavity mode resonance, light is confined into a low mode volume and high intensity electromagnetic mode inside the Si nanowire due to its high refractive index, which leads to strong SRS at low pump intensities. Electromagnetic calculations reveal greater than 6 orders of magnitude increase in Raman gain coefficient at 532 nm pump wavelength, compared to the gain value at 1.55 μm wavelength reported in literature, despite the 10 8 higher losses at 532 nm. Because of the high gain in such small structures, we believe that this is a significant first step in realizing a monolithically integrable nanoscale low-powered Si Raman laser.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Tuning the Quantum Dot (QD)/Mediator Interface for Optimal Efficiency of QD-Sensitized Near-Infrared-to-Visible Photon Upconversion Systems

Lead sulfide (PbS) quantum dots (QDs) have shown promising performance as a sensitizer in infrared-to-visible photon upconversion systems. To investigate the key design rules, we compare three PbS-sensitized upconversion systems using three mediator molecules with the same tetracene triplet acceptor at different distances from the QD. Using transient absorption spectroscopy, we directly measure the triplet energy-transfer rates and efficiencies from the QD to the mediator and from the mediator to the emitter. With increasing distance between the mediator and PbS QD, the efficiency of the first triplet energy transfer from the QD to the mediator decreases because of a decrease in the rate of this triplet energy-transfer step, while the efficiency of the second triplet energy transfer from the mediator to the emitter increases because of a reduction in the QD-induced mediator triplet state decay. The latter effect is a result of the slow rate constant of the second triplet energy-transfer process, which is 3 orders of magnitude slower than the diffusion-limited value. The combined results lead to a net decrease of the steady-state upconversion quantum yield with distance, which could be predicted by our kinetic model. Our result shows that the QD/mediator interface affects both the first and second triplet energy transfer processes in the photon upconversion system, and the QD/mediator distance has an opposite effect on the efficiencies of the first and second triplet energy transfer. Lastly, these findings provide important insight for the further rational improvement of the overall efficiency of QD-based upconversion systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Mechanistic Insights into Visible-Light-Induced ATRA Reactions Powered by the Symbiotic Relationship between Cu(II)/Cu(I) Phenanthroline Complexes

As photoredox catalysis continues to yield promising chemical transformations, there is an increased need to understand how specific photocatalysts function to improve reaction efficiencies while expanding their scope. Copper-phenanthroline-based photocatalysts such as Cu II (dap)Cl 2 (dap = 2,9-di(p-anisyl)-1,10-phenanthroline) and [Cu I (dap) 2 ]Cl were both found to be equally capable of olefin activation through electrophilic atom transfer radical addition (ATRA) reactions. Although these molecular catalysts have proven successful, many intermediates suggested in the proposed catalytic cycles have never been detected. One undetermined aspect in this chemistry is related to how one equivalent of Cu II (dap)Cl 2 generates half of an equivalent of [Cu I (dap) 2 ] + during the photocatalytic sequence. To this end, we initially used more synthetically accessible model systems, namely, [Cu I (dpp) 2 ]Cl and Cu II (dpp)Cl 2 (dpp = 2,9-diphenyl-1,10-phenanthroline), to glean detailed mechanistic insights into this unusual symbiotic relationship. We directly detected several intermediates involved in the ATRA photocatalytic cycle using these model chromophores in conjunction with electronic spectroscopy, infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) mass spectrometry, electronic structure calculations, EPR spin-trap experiments, and 1 H NMR spectroscopy. We found that the unique ligand lability and coordinating properties of acetonitrile enable both the in situ oxidation of [Cu I (dpp) 2 ] + by tosyl chloride into Cu II (dpp)Cl 2 and the visible-light-induced homolysis of the Cu II –Cl bond, which initiates the conversion to the Cu I species [Cu I (dpp) 2 ][Cu I Cl 2 ]. Here, the combined findings from the present study of the catalytic cycle demonstrate that the symbiotic relationship between Cu II (dpp)Cl 2 and [Cu I (dpp) 2 ] + , as well as between Cu II (dap)Cl 2 and [Cu I (dap) 2 ] + , is the critical factor enabling the ATRA photoreaction by departing from either photocatalyst.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Anatomy of a Visible Light Activated Photocatalyst for Water Splitting

The supported mixed oxide (Rh 2-y Cr y O 3 )/(Ga 1-x Zn x )(N 1-x O x ) photocatalyst, highly active for splitting of H 2 O, was extensively characterized for its bulk and surface properties with the objective of developing fundamental structure-photoactivity relationships. Raman and UV-vis spectroscopy revealed that the molecular and electronic structures, respectively, of the oxynitride (Ga 1-x Zn x )(N 1-x O x ) support are not perturbed by the deposition of the (Rh 2-y Cr y O 3 ) NPs. Photoluminescence (PL) spectroscopy, however, showed that the oxynitride (Ga 1-x Zn x )(N 1-x O x ) support is the source of excited electrons/holes and the (Rh 2-y Cr y O 3 ) NPs greatly reduce the undesirable recombination of photoexcited electron/holes by acting as efficient electron traps as well as increase the lifetimes of the excitons. High Resolution-XPS and High Sensitivity-LEIS surface analyses reveal that the surfaces of the (Rh 2-y Cr y O 3 ) NPs consist of Rh +3 and Cr +3 mixed oxide species. In Situ AP-XPS help to reveal that the Rh+3 and surface N atoms are involved in water splitting. Dispersed RhOx species on the (Ga 1-x Zn x )(N 1-x O x ) support and on CrO x NPs were found to be the photocatalytic active sites for H 2 generation and N and Zn sites from the (Ga 1-x Zn x )(N 1-x O x ) support are the photocatalytic active site for O 2 generation. In conclusion, the current investigation establishes the fundamental structure-photoactivity relationships of these visible light activated photocatalysts.

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

High-Redox-Potential Chromophores for Visible-Light-Driven Water Oxidation at Low pH

Photochemical water oxidation at low pH requires chromophores with adequate photophysical properties and high redox potentials capable of oxidizing the catalysts. We report here a series of homoleptic Ru(II) polypyridyl complexes and their performances in photochemical water oxidation at pH 1 using persulfate as the sacrificial electron acceptor. These chromophores incorporate CF 3 or PO 3 H 2 groups to increase the RuIII/II standard potentials to 1.3–1.6 V versus NHE, while their homoleptic nature retains photophysical properties (absorption spectra, lifetimes, emission energies, emission quantum yields) comparable to [Ru(bpy) 3 ] 2+ . With [(bda)Ru(isq) 2 ] as the catalyst, the chromophores promote visible-light-driven water oxidation with high activity at low pH. The chromophores with phosphonate groups as substituents showed higher activity than expected based on driving force arguments. In addition, kinetic isotope effects as high as ~3 were measured, suggesting the involvement of concerted proton-coupled transfer pathways between the catalyst and the chromophores with the phosphonate group acting as the proton acceptor. These chromophores therefore carry out the light absorption, charge migration, and proton transfer roles of P 680 , Tyr161, and His190 in Photosystem II on a single molecule and are good candidates for photoelectrochemical water oxidation at low pH in dye-sensitized photoelectrochemical cells.

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

Surface-Attached Molecular Catalysts on Visible-Light-Absorbing Semiconductors: Opportunities and Challenges for a Stable Hybrid Water-Splitting Photoanode

Hybrid photoanodes for water-splitting photoelectrochemical cells (WS-PECs) consist of a visible-light-absorbing semiconductor (VLASC) with a molecular water-oxidation catalyst (mWOC) attached, and show great promise for solar fuel generation. In this perspective, we will focus on the less emphasized but crucial subject of stability in these systems. The stability of each component, including the VLASC, the mWOC, and the connection of the two, must individually be considered, as well as how the system functions as a whole. We offer design strategies for each of these parts, as well as some characterization techniques helpful in the study of degradation. Lastly, we propose some future directions for the development of hybrid WS-PEC photoanodes with long-term stability that could be suitable for practical application.

14 SOLAR ENERGY↗