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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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Atomically dispersed Co–Fe dual sites on nitrogen doped microporous carbon are constructed for ORR with superior performance, while XAS, differential PDF dPDF and DFT studies reveal the relationship between the catalytic performance and the local chemical environment.
The de novo design of polar protein–protein interactions is challenging because of the thermodynamic cost of stripping water away from the polar groups. Here, we describe a general approach for designing proteins which complement exposed polar backbone groups at the edge of beta sheets with geometrically matched beta strands. We used this approach to computationally design small proteins that bind to an exposed beta sheet on the human transferrin receptor (hTfR), which shuttles interacting proteins across the blood–brain barrier (BBB), opening up avenues for drug delivery into the brain. We describe a design which binds hTfR with a 20 nM K d , is hyperstable, and crosses an in vitro microfluidic organ-on-a-chip model of the human BBB. Our design approach provides a general strategy for creating binders to protein targets with exposed surface beta edge strands.
Traces of life are nearly ubiquitous on Earth. However, a central unresolved question is whether these traces always indicate an active microbial community or whether, in extreme environments, such as hyperarid deserts, they instead reflect just dormant or dead cells. Although microbial biomass and diversity decrease with increasing aridity in the Atacama Desert, we provide multiple lines of evidence for the presence of an at times metabolically active, microbial community in one of the driest places on Earth. We base this observation on four major lines of evidence: (i) a physico-chemical characterization of the soil habitability after an exceptional rain event, (ii) identified biomolecules indicative of potentially active cells [e.g., presence of ATP, phospholipid fatty acids (PLFAs), metabolites, and enzymatic activity], (iii) measurements of in situ replication rates of genomes of uncultivated bacteria reconstructed from selected samples, and (iv) microbial community patterns specific to soil parameters and depths. We infer that the microbial populations have undergone selection and adaptation in response to their specific soil microenvironment and in particular to the degree of aridity. Collectively, our results highlight that even the hyperarid Atacama Desert can provide a habitable environment for microorganisms that allows them to become metabolically active following an episodic increase in moisture and that once it decreases, so does the activity of the microbiota. These results have implications for the prospect of life on other planets such as Mars, which has transitioned from an earlier wetter environment to today’s extreme hyperaridity.
Abstract The design principles of acceptor 1 –acceptor 2 copolymers featuring alternating diketopyrrolopyrrole (DPP) and thienopyrrolodione (TPD) moieties are investigated. The investigated series of polymers is obtained by varying the aromatic linker between the two acceptor motifs between thiophene, thiazole, pyridine, and benzene. High electron affinities between 3.96 and 4.42 eV, facilitated by the synergy of the acceptor motifs are determined with optical gaps between 1.37 and 2.02 eV. Grazing incidence wide‐angle X‐ray scattering studies reveal a range of film morphologies after thermal annealing, including face‐on, end‐on and superstructure edge‐on‐like crystallites. Conversely, all materials form thin edge‐on layers on the polymer–air interface, as demonstrated by multi‐elemental near‐edge X‐ray absorption fine‐structure spectroscopy. The benefit of the electron‐deficient linkers thiazole and pyridine is evident: In organic field effect transistors, electron mobilities of up to 4.6 × 10 −2 cm 2 V −1 s −1 are obtained with outstanding on/off current ratios of 5 × 10 5 , facilitated by the absence of detectable hole transport in these materials. Viability for all‐polymer solar cells is assessed in active layer blends with the donor polymer PM6, yielding a maximum average power conversion efficiency of 4.8% and an open circuit voltage above 1 V.
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Ni-based hydroxides are promising electrocatalysts for biomass oxidation reactions, supplanting the oxygen evolution reaction (OER) due to lower overpotentials while producing value-added chemicals. The identification and subsequent engineering of their catalytically active sites are essential to facilitate these anodic reactions. Herein, the proportional relationship between catalysts’ deprotonation propensity and Faradic efficiency of 5-hydroxymethylfurfural (5-HMF)-to-2,5 furandicarboxylic acid (FDCA, FEFDCA) is revealed by thorough density functional theory (DFT) simulations and atomic-scale characterizations, including in situ synchrotron diffraction and spectroscopy methods. The deprotonation capability of ultrathin layer-double hydroxides (UT-LDHs) is regulated by tuning the covalency of metal (M)-oxygen (O) motifs through defect site engineering and selection of M 3+ co-chemistry. NiMn UT-LDHs show an ultrahigh FE FDCA of 99% at 1.37 V versus reversible hydrogen electrode (RHE) and retain a high FE FDCA of 92.7% in the OER-operating window at 1.52 V, about 2× that of NiFe UT-LDHs (49.5%) at 1.52 V. Ni–O and Mn–O motifs function as dual active sites for HMF electrooxidation, where the continuous deprotonation of Mn–OH sites plays a dominant role in achieving high selectivity while suppressing OER at high potentials. The results showcase a universal concept of modulating competing anodic reactions in aqueous biomass electrolysis by electronically engineering the deprotonation behavior of metal hydroxides, anticipated to be translatable across various biomass substrates.
Abstract All‐perovskite tandem solar cells show great potential to enable the highest performance at reasonable costs for a viable market entry in the near future. In particular, wide‐bandgap (WBG) perovskites with higher open‐circuit voltage ( V OC ) are essential to further improve the tandem solar cells’ performance. Here, a new 1.8 eV bandgap triple‐halide perovskite composition in conjunction with a piperazinium iodide (PI) surface treatment is developed. With structural analysis, it is found that the PI modifies the surface through a reduction of excess lead iodide in the perovskite and additionally penetrates the bulk. Constant light‐induced magneto‐transport measurements are applied to separately resolve charge carrier properties of electrons and holes. These measurements reveal a reduced deep trap state density, and improved steady‐state carrier lifetime (factor 2.6) and diffusion lengths (factor 1.6). As a result, WBG PSCs achieve 1.36 V V OC , reaching 90% of the radiative limit. Combined with a 1.26 eV narrow bandgap (NBG) perovskite with a rubidium iodide additive, this enables a tandem cell with a certified scan efficiency of 27.5%.
Abstract Optically addressable light valves (OALVs) are specialized optical components utilized for spatial beam shaping in various laser‐based applications, including optics damage mitigation, and enhanced functionality in diode‐based additive manufacturing requiring high intensities. Current state‐of‐the‐art OALVs employ photoconductors such as Bismuth Silicon Oxide (BSO) or Bismuth Germanium Oxide (BGO), which suffer from limited laser‐induced damage thresholds (LiDT) and inadequate thermal conductivities, thus restricting their use in high peak and average power applications. Aluminum nitride (AlN), an emerging ultra‐wide band gap (UWBG) III–V semiconductor, offers promising optoelectronic properties and superior thermal conductivity (>300 Wm −1 K −1 at 298° K, compared to BSO's 3.29 Wm −1 K −1 ). In this study, the first AlN‐based OALVs are designed, fabricated, and experimentally demonstrated using commercially available single‐crystal AlN substrates. These AlN‐based OALVs have shown clear superiority over BSO and BGO‐based devices. Design considerations for OALVs incorporating UWBG photoconductors are discussed, and the photoresponsivity from defect‐mediated sub‐bandgap absorption in AlN crystals is verified as sufficient for OALVs operating under high light fluences. The optimum driving voltage for the AlN‐based OALV is determined to be ≈ 45 V pp at 100 Hz, achieving a transmittance of 91.3%, an extinction ratio (ER) of more than 100, and a 51:1 image contrast.
Abstract Previous efforts to understand structure‐function relationships in high ionic conductivity materials for solid state batteries have predominantly relied on density functional theory (DFT‐) based ab initio molecular dynamics (MD). Such simulations, however, are computationally demanding and cannot be reasonably applied to large systems containing more than a hundred atoms. Here, an artificial neural network (ANN) is trained to accelerate the calculation of high accuracy atomic forces and energies used during such MD simulations. After carefully training a robust ANN for four and five element systems, nearly identical lithium ion diffusivities are obtained for Li 10 GeP 2 S 12 (LGPS) when benchmarking the ANN‐MD results with DFT‐MD. Applying the ANN‐MD approach, the effect of chlorine doping on the lithium diffusivity is calculated in an LGPS‐like structure and it is found that a dopant concentration of 1.3% maximizes ionic conductivity. The optimal concentration balances the competing consequences of effective atomic radii and dielectric constants on lithium diffusion and agrees with the experimental composition. Performing simulations at the resolution necessary to model experimentally relevant and optimal concentrations would be infeasible with traditional DFT‐MD. Systems that require a large number of simulated atoms can be studied more efficiently while maintaining high accuracy with the proposed ANN‐MD framework.
“Anode-free” solid-state batteries (SSBs), which have no anode active material, can exhibit extremely high energy density (≈1500 Wh L -1 ). However, there is a lack of understanding of the lithium plating/stripping mechanisms at initially lithium-free solid-state electrolyte (SSE) interfaces because excess lithium metal is often used. Here, it is demonstrated that commercially relevant quantities of lithium (>5 mAh cm -2 ) can be reliably plated at moderate current densities (1 mA cm -2 ) using the sulfide SSE Li 6 PS 5 Cl. Investigations of lithium plating/stripping mechanisms, in conjunction with cryo-ocused ion beam (FIB) imaging, synchrotron tomography, and phase-field modeling, reveal that the cycling stability of these cells is fundamentally limited by the nonuniform presence of lithium during stripping. Local lithium depletion causes isolated lithium regions toward the end of stripping, decreasing electrochemically active area and resulting in high local current densities and void formation. This accelerates subsequent filament growth and short circuiting compared to lithium-excess cells. Despite this degradation mode, here it is shown that anode-free cells exhibit comparable Coulombic efficiency to lithium-excess cells, and improved resistance to short circuiting is achieved by avoiding local lithium depletion through retention of thicker lithium at the interface. These new insights provide a foundation for engineering future high-energy anode-free SSBs.
Abstract Electrochemical biomass oxidation coupled with hydrogen evolution offers a promising route to generate value‐added chemicals and clean energy. The complex adsorption behavior of 5‐hydroxymethyl furfural (HMF) and hydroxyl ions (OH − ) on the electrocatalyst surface during HMF electrooxidation reaction (HMFOR) necessitates an in‐depth understanding of active sites available for adsorption. Herein, oxygen vacancy (V O ) defects are introduced in NiFe layered double hydroxide (LDH) using Ce dopants to manipulate electronic structure. Synchrotron‐based HE‐XRD and XAS indicate negligible V O in La‐doped NiFe while Ce doping leads to V O defects due to flexible Ce redox (Ce 3+ ↔ Ce 4+ ). The V O ‐rich Ce‐NiFe exhibits higher Faradic efficiency of ≈90% to produce 2,5‐furan dicarboxylic acid (FDCA), far greater than ≈60% for NiFe V O in Ce‐NiFe act as alternative active sites for OH − adsorption, hence reducing adsorption competition for the same metal sites. DFT calculation results corroborate experimental findings by showcasing that the presence of V O in Ce‐NiFe manipulates the adsorption energies and facilitates the chemical adsorption OH − in V O to improve HMFOR. In situ HE‐XRD derived pair distribution function coupled to RMC simulations confirm OH − trapping in V O and HMF adsorption on metal centers as evident by interlayer distance evolution. Taken together, this work showcases routes for dual‐site electrocatalyst design for improved biomass electrooxidation.
Abstract Achieving both high redox activity and rapid ion transport is a critical and pervasive challenge in electrochemical energy storage applications. This challenge is significantly magnified when using large‐sized charge carriers, such as the sustainable ammonium ion (NH 4 + ). A self‐assembled MXene/n‐type conjugated polyelectrolyte (CPE) superlattice‐like heterostructure that enables redox‐active, fast, and reversible ammonium storage is reported. The superlattice‐like structure persists as the CPE:MXene ratio increases, accompanied by a linear increase in the interlayer spacing of MXene flakes and a greater overlap of CPEs. Concurrently, the redox activity per unit of CPE unexpectedly intensifies, a phenomenon that can be explained by the enhanced de‐solvation of ammonium due to the increased volume of 3 Å‐sized pores, as indicated by molecular dynamic simulations. At the maximum CPE mass loading (MXene:CPE ratio = 2:1), the heterostructure demonstrates the strongest polymeric redox activity with a high ammonium storage capacity of 126.1 C g −1 and a superior rate capability at 10 A g −1 . This work unveils an effective strategy for designing tunable superlattice‐like heterostructures to enhance redox activity and achieve rapid charge transfer for ions beyond lithium.
Abstract Perovskite solar cells (PSCs) are promising for high‐efficiency tandem applications, but their long‐term stability, particularly due to ion migration, remains a challenge. Despite progress in stabilizing PSCs, they still fall short compared to mature technologies like silicon. This study explores how different piperazinium salt treatments using iodide, chloride, tosylate, and bistriflimide anions affect the energetics, carrier dynamics, and stability of 1.68 eV bandgap PSCs. Chloride‐based treatments achieved the highest power conversion efficiency (21.5%) and open‐circuit voltage (1.28 V), correlating with stronger band bending and n‐type character at the surface. At the same time, they showed reduced long‐term stability due to increased ionic losses. Tosylate‐treated devices offered the best balance, retaining 96.4% efficiency after 1000 h (ISOS‐LC‐1I). These findings suggest that targeted surface treatments can enhance both efficiency and stability in PSCs.
Abstract INTRODUCTION Tau‐positron emission tomography (PET) outcome data of patients with Alzheimer's disease (AD) cannot currently be meaningfully compared or combined when different tracers are used due to differences in tracer properties, instrumentation, and methods of analysis. METHODS Using head‐to‐head data from five cohorts with tau PET radiotracers designed to target tau deposition in AD, we tested a joint propagation model (JPM) to harmonize quantification (units termed “CenTauR” [CTR]). JPM is a statistical model that simultaneously models the relationships between head‐to‐head and anchor point data. JPM was compared to a linear regression approach analogous to the one used in the amyloid PET Centiloid scale. RESULTS A strong linear relationship was observed between CTR values across brain regions. Using the JPM approach, CTR estimates were similar to, but more accurate than, those derived using the linear regression approach. DISCUSSION Preliminary findings using the JPM support the development and adoption of a universal scale for tau‐PET quantification. Highlights Tested a novel joint propagation model (JPM) to harmonize quantification of tau PET. Units of common scale are termed “CenTauRs”. Tested a Centiloid‐like linear regression approach. Using five cohorts with head‐to‐head tau PET, JPM outperformed linearregressionbased approach. Strong linear relationship was observed between CenTauRs values across brain regions.
Abstract Plasma wakefield accelerators offer accelerating and focusing electric fields three to four orders of magnitude larger than state‐of‐the‐art radiofrequency cavity‐based accelerators. Plasma photocathodes can release ultracold electron populations within such plasma waves and thus open a path toward tunable production of well‐defined, compact electron beams with normalized emittance and brightness many orders of magnitude better than state‐of‐the‐art. Such beams will have far‐reaching impact for applications such as light sources, but also open up new vistas on high energy and high field physics. This paper reviews the innovation of plasma photocathodes, and reports on the experimental progress, challenges, and future prospects of the approach. Details of the proof‐of‐concept demonstration of a plasma photocathode in 90° geometry at SLAC FACET within the E‐210: Trojan Horse program are described. Using this experience, alongside theoretical and simulation‐supported advances, an outlook is given on future realizations of plasma photocathodes such as the upcoming E‐310: Trojan Horse‐II program at FACET‐II with prospects toward excellent witness beam parameter quality, tunability, and stability. Future installations of plasma photocathodes also at compact, hybrid plasma wakefield accelerators, will then boost capacities and open up novel capabilities for experiments at the forefront of interaction of high brightness electron and photon beams.
Abstract Bifunctional catalysis in zeolites possessing both Brønsted and Lewis acid sites offers unique opportunities to tailor shape selectivity and enhance catalyst performance. Here, we examine the impact of framework and extra‐framework gallium species on enriched aromatics production in zeolite ZSM‐5. We compare three distinct methods of preparing Ga‐ZSM‐5 and reveal direct (single step) synthesis leads to optimal catalysts compared to post‐synthesis methods. Using a combination of state‐of‐the‐art characterization, catalyst testing, and density functional theory calculations, we show that Ga Lewis acid sites strongly favor aromatization. Our findings also suggest Ga(framework)–Ga(extra‐framework) pairings, which can only be achieved in materials prepared by direct synthesis, are the most energetically favorable sites for reaction pathways leading to aromatics. Calculated acid site exchange energies between extra‐framework Ga at framework sites comprised of either Al or Ga reveal a site‐specific preference for stabilizing Lewis acids, which is qualitatively consistent with experimental measurements. These findings indicate the possibility of tailoring Lewis acid siting by the placement of Ga heteroatoms at distinct tetrahedral sites in the zeolite framework, which can have a marked impact on catalyst performance relative to conventional H‐ZSM‐5.
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