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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Nanoscale Measurements of Charge Transfer at Cocatalyst/Semiconductor Interfaces in BiVO 4 Particle Photocatalysts

Semiconductor photocatalyst particles convert solar energy to fuels like H 2 . The particles are often assumed to provide crystalline-facet-dependent electron-hole separation. A common strategy is to deposit HER electrocatalyst on electron-selective facets and OER electrocatalyst on hole-selective facets. A precise understanding of how charge-carrier-selective contacts emerges and how they rationally designed, however, is missing. Using a combination of ex-situ and in-situ conducting-AFM experiments and new ionomer/catalyst-semiconductor test structures, we show how heterogeneity in charge-carrier selectivity can be measured at the nanoscale. We discover that the presence of interface water/electrolyte is critical to induce hole selectivity between the CoO x water-oxidation catalyst and the BiVO 4 light absorber. pH-dependent measurements suggest that negative surface charge on the semiconductor is central to inducing hole selectivity. Furthermore, the work also demonstrates a new approach to control local pH and introduce water using thin-film ionomers compatible with conductive-AFM measurements.

14 SOLAR ENERGY↗
DOE OSTI2018

Controlled Generation of TiO x –Au Interface Using Titanium Molecular Complex Bearing Pyridyl Anchors: Synthesis, Characterization and Catalysis

Interfacial perimeter sites between metal and support are often important for catalysis. A mononuclear titanium siloxy complex III, Ti(acac) 2 [OSiC 6 H 5 N(OCH 3 ) 2 ] 2 was synthesized to generate TiOx units of different degrees of clustering to decorate Au nanoparticles. Two different methods of preparation were examined; one was to deposit III onto Au/SiO 2 and the other was to form III-covered Au nanoparticle first before deposition onto SiO 2 . The former method generated more highly dispersed TiO x units, while larger domains of TiO 2 were formed with the latter method, as deduced by UV–vis and XAS characterization. A model was proposed to explain how TiO x dispersity could be related to the preparative procedures. These samples were further tested as catalysts in selective oxidation of propane in a stream of O 2 and H 2 . They exhibited different product selectivities. The sample with more dispersed TiO x units were more selective for acetone formation versus propene formation. The results confirmed the important role of both the Au–TiO x interface at the perimeter and the extent of Ti isolation in the TiO x phase in the reaction.

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

Designing Nanoplatelet Alloy/Nafion Catalytic Interface for Optimization of PEMFCs: Performance, Durability, and CO Resistance

We have adapted the two phase Brust method to synthesize large quantities of AuPd alloy nanoparticles with diameter of 1.86 ± 0.40 nm. When the particles were spread at the air water interface of a Langmuir Blodgett (LB) trough, they exhibited a distinct pressure area isotherm curve. The X-ray reflectivity (XRR) shows the formation of an incompressible monolayer with uniform thickness of 1.16 ± 0.02 nm at low pressures which collapses to form a second layer with 2.13 nm thick at higher pressures. High resolution transmission electron microscopy (HRTEM) imaging of the monolayer indicates that the particles are highly crystalline, with well-defined atomic planes and self-assembly into a hexagonal structure. Extended X-ray absorption fine structure (EXAFS) analysis of the LB lift-off films only shows Au-Au and Au-Pd configurations, consistent with the formation of random alloy rather than core shell structure. When the particle monolayer was lifted onto the Nafion membrane of a proton exchange membrane fuel cell (PEMFC), a maximum power output of 0.54 W/cm 2 was obtained with a Pt loading of only 0.15 mg/cm 2 and 0.05 mg/cm 2 at the cathode and anode, respectively. This represents a 15% enhancement, which persists even after 30k cycles, relative to a membrane electrode assembly (MEA) using a non-coated membrane. Density function theory (DFT) modeling of the hexagonally packed platelet nanoparticle alloy structure deposited on Nafion predicted that the SO 3 functionality serves a similar function to metal oxide supports in reducing the activation barrier for the CO oxidation reaction. This was confirmed by measuring the power output of a PEMFC when 0.1% CO was mixed either into the input H 2 stream at the anode or with O 2 at the cathode. In the uncoated MEAs, a significant decrease of 72% and 61% was measured when CO was introduced at the anode and cathode, respectively, while MEAs with coated particle membranes only experienced a decrease of 21% and 17%, respectively. These results indicate that a synergy can be established between the nanoparticle platelets and the surface of the Nafion membrane which can produce CO resistant PEMFC that could operate at ambient temperatures on impure, but abundant hydrogen gas such as those produced by reformate or electrolysis processes. Furthermore the availability of inexpensive H 2 opens opportunities for gas distribution and greatly facilitates the commercialization of PEMFCs, which will conform to the ambitious goals set by the Department of Energy (DOE) for 2020.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

Nature of the Interfaces Between Stoichiometric and Under-Stoichiometric MoO 3 and 4,4'- N , N '-dicarbazole-biphenyl: A Combined Theoretical and Experimental Study

A combination of density functional theory and experimental measurements via ultraviolet and X-ray photoelectron spectroscopies is used to explore the nature of the interface between the stoichiometric molybdenum trioxide (MoO3) or its under-stoichiometric counterpart with oxygen vacancies, and an organic hole-transport layer represented by 4,4'-N,N'-dicarbazole-biphenyl (CBP). Upon adsorption of CBP, special attention is paid to i) the appearance of gap states and the reduction of the molybdenum oxide surface, and ii) the evolution of the work function. Very good agreement is found between theory and experiment. The near alignment of the CBP highest occupied molecular orbital with the Fermi level and the conduction band edge of molybdenum oxide points to facile hole collection or injection.

36 MATERIALS SCIENCE↗
DOE OSTI2019

NIR Biosensing of Neurotransmitters in Stem Cell‐Derived Neural Interface Using Advanced Core–Shell Upconversion Nanoparticles

Abstract Nondestructive neurotransmitter detection and real‐time monitoring of stem cell differentiation are both of great significance in the field of neurodegenerative disease and regenerative medicine. Although luminescent biosensing nanoprobes have been developed to address this need, they have intrinsic limitations such as autofluorescence, scattering, and phototoxicity. Upconversion nanoparticles (UCNPs) have gained increasing attention for various biomedical applications due to their high photostability, low auto‐fluorescent background, and deep tissue penetration; however, UCNPs also suffer from low emission intensities due to undesirable energy migration pathways. To address the aforementioned issue, a single‐crystal core–shell–shell “sandwich” structured UCNP is developed that is designed to minimize deleterious energy back‐transfer to yield bright visible emissions using low power density excitations. These UCNPs show a remarkable enhancement of luminescent output relative to conventional β‐NaYF4:Yb,Er codoped UCNPs and β‐NaYF4:Yb,Er@NaYF4:Yb “active shell” alike. Moreover, this advanced core–shell–shell UCNP is subsequently used to develop a highly sensitive biosensor for the ultrasensitive detection of dopamine released from stem cell‐derived dopaminergic‐neurons. Given the challenges of in situ detection of neurotransmitters, the developed NIR‐based biosensing of neurotransmitters in stem cell‐derived neural interfaces present a unique tool for investigating single‐cell mechanisms associated with dopamine, or other neurotransmitters, and their roles in neurological processes.

Rabie, Hudifah↗
DOE OSTI2016

Complex collective dynamics of active torque-driven colloids at interfaces

Modern self-assembly techniques aiming to produce complex structural order or functional diversity often rely on non-equilibrium conditions in the system. Light, electric, or magnetic fields are predominantly used to modify interaction profiles of colloidal particles during self-assembly or induce complex out-of-equilibrium dynamic ordering. The energy injection rate, properties of the environment are important control parameters that influence the outcome of active (dynamic) self-assembly. The current review is focused on a case of collective dynamics and self-assembly of particles with externally driven torques coupled to a liquid or solid interface. The complexity of interactions in such systems is further enriched by strong hydrodynamic coupling between particles. Unconventionally ordered dynamic self-assembled patterns, spontaneous symmetry breaking phenomena, self-propulsion, and collective transport have been reported in torque-driven colloids. Some of the features of the complex collective behavior and dynamic pattern formation in those active systems have been successfully captured in simulations.

Snezhko, Alexey↗
DOE OSTI2021

Friction Stir Dovetailing of AA7099 to Steel with AA6061 Interlayer for Reduced Zn Embrittlement at Dissimilar Interface

Joining of high strength Al alloy (AA7099) to steel (rolled homogeneous armor) with and without AA6061 interlayer was achieved using a friction stir dovetailing (FSD) method. Detailed investigations were conducted to establish correlations between mechanical performance and microstructural evolution of FSD joints. Lap shear tensile testing revealed that incorporation of the AA6061 interlayer combined with tailored processing methodology significantly improved both mechanical interlocking and load transmission across the dovetail interface. Following incorporation of the interlayer, the maximum load carrying capacity and peak extension (of the AA7099/AA6061/steel joint) are 60% and 210% higher, respectively, than results obtained from an AA7099/steel joint without an interlayer. Without an AA6061 interlayer, formation of zinc rich intermetallic compounds led to brittle interfacial failure of the AA7099-steel FSD joint. Incorporation of novel tool and joint configuration eliminated asymmetric joint performance as a function of loading direction, which is generally observed in friction stir lap welding. The efficacy of the use of an AA6061 interlayer in joining AA7099 to steel was demonstrated through mechanical testing as well as high resolution analytical electron microscopy characterization.

Dissimilar metal joining, Friction stir dovetailin↗
DOE OSTI2019

Synergistic Coupling of Proton Conductors BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3–δ and La 2 Ce 2 O 7 to Create Chemical Stable, Interface Active Electrolyte for Steam Electrolysis Cells

For the first time, proton conductors BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3–δ (BZCYYb) and La 2 Ce 2 O 7 (LCO) are combined to create an interface active and steam-tolerant electrolyte for high-performance proton-conducting solid oxide electrolysis cells. LCO shows good chemical compatibility with BZCYYb. The readily fabricated LCO/BZCYYb bilayer electrolyte can be densified at a temperature of as low as 1300 °C versus ~1600 °C for the benchmark steam-stable BaZr 0.8 Y 0.2 O 3–δ electrolyte. With Pr 2 NiO 4+δ as the anode and Ni as the cathode catalyst, this bilayer electrolyte cell yields a current density of 975 and 300 mA/cm 2 under a 1.3 V applied potential at 700 and 600 °C, respectively. This performance is among the best of all H-SOECs equipped with a chemically stable electrolyte so far. A BZCYYb layer in the bilayer electrolyte promotes the hydrogen evolution reaction at the cathode side, resulting in a 108% improvement over the cell without this layer. The LCO layer, on the other hand, effectively protects this functional BZCYYb layer from the high concentration of steam in a practical SOEC operation condition. The cell without the LCO layer shows degradation in terms of an increased electrolyzing potential from 1.07 to 1.29 V during a constant 400 mA/cm 2 operation at 700 °C. In contrast, the bilayer electrolyte cell maintains the same electrolyzing potential of 1.13 V under the same conduction for a 102 h operation. These findings demonstrate that this synergic bilayer electrolyte design is a vital strategy to overcome the dilemma between performance and stability faced by the current benchmark Zr- or Ce-rich Ba(CeZr)O 3–δ electrolysis cells to achieve excellent performance and stability at the same time.

36 MATERIALS SCIENCE↗