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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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46 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Advancing Insights into Electrochemical Pre‐Treatments of Supported Nanoparticle Electrocatalysts by Combining a Design of Experiments Strategy with In Situ Characterization

Activation, break-in, and/or pre-treatment protocols are generally applied to energy conversion devices before regular operation to reach stable performance. There remains much to understand about the relationships among physical properties, performance, and electrochemical pre-treatments. Here, a design-of-experiments (DoE) strategy is employed to address this gap by demonstrating the influence of five pre-treatment parameters for carbon-supported Pt-nanoparticle catalysts on the electrocatalytic oxygen reduction reaction (ORR). A subset of pre-treatments, developed using a central composite design, are tested in a flow cell combined with an inductively-coupled plasma mass spectrometer (on-line ICP-MS). The DoE-based approach facilitates comprehensive insights from two orders of magnitude fewer experiments than a conventional grid search. The coupled on-line ICP-MS setup enables effective catalysis and real-time catalyst dissolution data. Leveraging insights from DoE for on-line ICP-MS and additional characterization, a model is built between the degradation of a multi-dimensional supported Pt surface, its performance, and applied electrochemical parameters. These investigations identify surface modifications, such as oxidation, and subsequent restructuring of Pt during pre-treatment as a primary cause of performance deterioration during ORR. By combining DoE with advanced characterization techniques, a powerful approach is demonstrated to gain a mechanistic understanding of pre-treatment protocols that can be broadly adapted to various reaction chemistries.

Platinum↗
DOE OSTI2023

Room Temperature Electrorefining of Rare Earth Metals from End-of-use Nd-Fe-B Magnets

Recovering rare earth elements (REE) from used permanent magnets, which contains about 30 wt.% of rare earth elements, has been persistent technological challenge. Current recycling methods relies on pyrometallurgical or hydrometallurgical processes which are energy- and chemical- intensive and not economically and environmentally viable for rare earth containing magnets. Enabling efficient and simplistic recovery and refining of REEs contained in End-of-Use (EoU) products, such as Neodymium-Iron-Boron (Nd-Fe-B) based magnets will play an important and complementary role in the total supply of REEs in the future. We designed a new electrochemical method and demonstrated a room temperature one-pot process that concurrently separates and electroplates REE from commercial Nd-Fe-B magnets. By establishing selective oxidation and reductive potential as electrochemical control parameter along with electrochemically compatible non-aqueous electrolyte system, we demonstrated selective electroleaching of lanthanides (Nd and Preseodymium (Pr)) from anode and concurrent plating as alloy at Pt cathode. The morphological and chemical evolution of the Nd-Fe-B magnets during electroleaching reveals the electrochemical stimuli and rate of dissolution depends on microstructural complexities of the Nd-Fe-B magnet. The concomitant electroplating process leads to Nd-Pr based alloy which can be used as raw metallic alloy for manufacturing new permanent magnet and other devices. Our study demonstrates a scalable separation and refining methodology, based on widely available organic electrolyte system and without any consumptive chemical use, for selective lanthanide recovery from waste magnets.

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

Platinum/Tantalum Carbide Core–Shell Nanoparticles with Sub‐Monolayer Shells for Methanol and Oxygen Electrocatalysis

Abstract Core–shell architectures provide great opportunities to improve catalytic activity, but achieving nanoparticle stability under electrochemical cycling remains challenging. Herein, core–shell nanoparticles comprising atomically thin Pt shells over earth‐abundant TaC cores are synthesized and used as highly durable electrocatalysts for the methanol oxidation reaction (MOR) and the oxygen reduction reaction (ORR) needed to drive direct methanol fuel cells (DMFCs). Characterization data show that a thin oxidic passivation layer protects the TaC core from undergoing dissolution in the fuel cell‐relevant potential range, enabling the use of partially covered Pt/TaC core–shell nanoparticles for MOR and ORR with high stability and enhanced catalytic performance. Specifically, at the anode the surface‐oxidized TaC further enhances MOR activity compared to conventional Pt nanoparticles. At the cathode, the Pt/TaC catalyst feature increases tolerance to methanol crossover. These results show unique synergistic advantages of the core–shell particles and open opportunities to tailor catalytic properties for electrocatalytic reactions.

Chemistry↗
DOE OSTI2024

Small, solubilized platinum nanocrystals consist of an ordered core surrounded by mobile surface atoms

In situ structures of Platinum (Pt) nanoparticles (NPs) can be determined with graphene liquid cell transmission electron microscopy. Atomic-scale three-dimensional structural information about their physiochemical properties in solution is critical for understanding their chemical function. We here analyze eight atomic-resolution maps of small (<3 nm) colloidal Pt NPs. Their structures are composed of an ordered crystalline core surrounded by surface atoms with comparatively high mobility. 3D reconstructions calculated from cumulative doses of 8500 and 17,000 electrons/pixel, respectively, are characterized in terms of loss of atomic densities and atomic displacements. Less than 5% of the total number of atoms are lost due to dissolution or knock-on damage in five of the structures analyzed, whereas 10–16% are lost in the remaining three. Less than 5% of the atomic positions are displaced due to the increased electron irradiation in all structures. The surface dynamics will play a critical role in the diverse catalytic function of Pt NPs and must be considered in efforts to model Pt NP function computationally.

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

Effective Corrosion-Resistant Single-Atom Alloy Catalyst on HfO 2 -Passivated BiVO 4 Photoanode for Durable (≈800 h) Solar Water Oxidation

Green hydrogen (H 2 ) production from solar water splitting necessitates photoelectrodes with superior photoelectrochemical (PEC) activity and durability. However, surface defects and photocorrosion instability—especially at high potentials—limit PEC performance and stability. Herein, the prototypical bismuth vanadate (BiVO 4 ) photoanode is used to demonstrate a holistic approach to improve photocurrent density and long-term stability. In this approach, high surface-area nanostructuring of BiVO 4 is combined with barium (Ba) doping with semi-crystalline hafnium oxide (HfO 2 ) surface passivation and single-atom nickel platinum (NiPt) catalysts. The introduction of Ba 2+ ions into BiVO 4 increases the concentration of conductive V 4+ ions or the ratio of V 4+ ions to oxygen vacancies, avoiding V 5+ dissolution during water oxidation. The semi-crystalline HfO 2 , which serves as a passivation layer, prevents BiVO 4 photocorrosion by suppressing harmful chemical reactions when holes are transferred to the electrolyte. The synergistic use of isolated single-atom and Ni-Pt coordination improves charge transfer at the photoanode/electrolyte interface, leading to enhanced PEC kinetics and stability. As a result, a photoelectrode is demonstrated with ≈6.5 mA cm -2 at 1.23 V versus a reversible hydrogen electrode (RHE) and continuous operation for 800 h with a negligible degradation rate. This work provides a promising approach to improve photoanodes for PEC H 2 production.

08 HYDROGEN↗
DOE OSTI2020

Nitride stabilized core/shell nanoparticles

Nitride stabilized metal (M or Pt(M)) nanoparticles and methods for their manufacture are disclosed. In one embodiment the metal nanoparticles have a nonporous noble metal shell with a nitride-stabilized non-noble metal core. The nitride-stabilized core provides a stabilizing effect under high oxidizing conditions suppressing the noble metal dissolution during potential cycling. Introduction of nitrogen into the core by annealing produces metal nitride(s) that are less susceptible to dissolution during potential cycling under high oxidizing conditions.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Recent developments in catalyst-related PEM fuel cell durability

Cost and durability remain the two major barriers to the widespread commercialization of polymer electrolyte membrane fuel cell (PEMFC)-based power systems, especially for the most impactful but challenging fuel cell electric vehicle (FCEV) application. Commercial FCEVs are now on the road; however, their PEMFC systems do not meet the cost targets established by the U.S. Department of Energy, primarily due to the high platinum loading needed on the cathode to achieve the requisite performance and lifetime. Furthermore, while the activities of a number of commercial Pt-based alloy cathode catalysts exceed the beginning-of-life (BOL) targets, these activities, and the overall cathode performance, degrade via a variety of mechanisms described herein. Degradation is mitigated in current FCEVs by utilizing a cathode catalyst with a lower BOL activity (e.g., much lower transition metal alloy content and larger BOL nanoparticle size), necessitating higher catalyst loadings, and through the utilization of system controls that avoid conditions known to exacerbate degradation processes, such as limiting the fuel cell stack voltage range. The design and development of active and robust materials and eliminating the need for vehicle mitigation strategies would greatly simplify the operating system, allowing for greater transient operation, avoiding large hybridization, and curtailing of fuel cell power. Although system mitigation strategies have provided the near-term pathway for FCEV commercialization, material-specific solutions are required to further reduce costs and improve operability and efficiency. Future material developments should focus on stabilization of the electrode structure and minimization of the catalyst particle susceptibility to dissolution caused by oxide formation and reduction over PEMFC cathode-relevant operating potentials plus minimization of support corrosion. Ex situ accelerated stress tests have provided insight into the processes responsible for material and performance degradation and will continue to provide useful information on the relative stability of materials and benchmarks for robust and stable materials-based solutions not requiring system mitigation strategies to achieve adequate lifetime.

25 ENERGY STORAGE↗
DOE OSTI2022

The high-pressure lithium-palladium and lithium-palladium-hydrogen systems

The lithium-palladium and lithium-palladium-hydrogen systems are investigated at high pressures at and above room temperature. Two novel lithium-palladium compounds are found below 18.7 GPa. An ambient temperature phase is tentatively assigned as $F\bar{4}3m$ Li 17 Pd 4 , with a = 17.661(1) Å at 8.64 GPa, isostructural with Li 17 Sn 4 . The other phase occurs at high-temperature and is $I\bar{4}3m$ Li 11 Pd 2 , a = 9.218(1) Å at 3.88 GPa and 200 °C, similar to Li 11 Pt 2 , which is also known at high pressure. The presence of hydrogen in the system results in an $I\bar{4}3m$ structure with a = 8.856(1) Å at 9.74 GPa. This persists up to 13.3 GPa, the highest pressure studied. Below 2 GPa an fcc phase with a large unit cell, a = 19.324(1) Å at 0.39 GPa, is also observed in the presence of hydrogen. On heating the hydrogen containing system at 4 GPa the $I\bar{4}3m$ phases persists to the melting point of lithium. In both systems melting the lithium results in the loss of crystalline diffraction from palladium containing phases. This is attributed to dissolution of the palladium in the molten lithium, and on cooling the palladium remains dispersed.

Frost, Mungo↗
DOE OSTI2022

The high-pressure lithium–palladium and lithium–palladium–hydrogen systems

Abstract The lithium–palladium and lithium–palladium–hydrogen systems are investigated at high pressures at and above room temperature. Two novel lithium–palladium compounds are found below $${18.7}\,{\mathrm{GPa}}$$ 18.7 GPa . An ambient temperature phase is tentatively assigned as $$F{\bar{4}}3m\,\hbox {Li}_{17}\hbox {Pd}_{4}$$ F 4 ¯ 3 m Li 17 Pd 4 , with $$a = 17.661(1)$$ a = 17.661 ( 1 ) Å at 8.64 GPa, isostructural with $$\hbox {Li}_{17}\hbox {Sn}_{4}$$ Li 17 Sn 4 . The other phase occurs at high-temperature and is $$I{\bar{4}}3m\, \hbox {Li}_{11}\hbox {Pd}_{2}$$ I 4 ¯ 3 m Li 11 Pd 2 , $$a = 9.218(1)$$ a = 9.218 ( 1 ) Å at 3.88 GPa and 200 $$^\circ {\mathrm{C}}$$ ∘ C , similar to $$\hbox {Li}_{11}\hbox {Pt}_{2}$$ Li 11 Pt 2 , which is also known at high pressure. The presence of hydrogen in the system results in an $$I{\bar{4}}3m$$ I 4 ¯ 3 m structure with $$a = 8.856(1)$$ a = 8.856 ( 1 ) Å at 9.74 GPa. This persists up to $${13.3}\,\mathrm{GPa}$$ 13.3 GPa , the highest pressure studied. Below $${2}\,{\mathrm{GPa}}$$ 2 GPa an fcc phase with a large unit cell, $$a = 19.324(1)$$ a = 19.324 ( 1 ) Å at 0.39 GPa, is also observed in the presence of hydrogen. On heating the hydrogen containing system at 4 GPa the $$I{\bar{4}}3m$$ I 4 ¯ 3 m phases persists to the melting point of lithium. In both systems melting the lithium results in the loss of crystalline diffraction from palladium containing phases. This is attributed to dissolution of the palladium in the molten lithium, and on cooling the palladium remains dispersed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗