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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Dynamic Promotion of the Oxygen Evolution Reaction via Programmable Metal Oxides

Hydrogen gas is a promising renewable energy storage medium when produced via water electrolysis, but this process is limited by the sluggish kinetics of the anodic oxygen evolution reaction (OER). Herein, we used a microkinetic model to investigate promoting the OER using programmable oxide catalysts (i.e., forced catalyst dynamics). We found that programmable catalysts could increase current density at a fixed overpotential (100–600× over static rates) or reduce the overpotential required to reach a fixed current density of 10 mA cm –2 (45–140% reduction vs static). In our kinetic parametrization, the key parameters controlling the quality of the catalytic ratchet were the O*-to-OOH* and O*-to-OH* activation barriers. Furthermore, our findings indicate that programmable catalysts may be a viable strategy for accelerating the OER or enabling lower-overpotential operation, but a more accurate kinetic parametrization is required for precise predictions of performance, ratchet quality, and resulting energy efficiency.

Catalysts↗
DOE OSTI2024

Solution-Phase Synthesis of Platinum-Decorated Hydrogen Tungsten Bronzes for Hydrogen Atom Transfer from Oxides to Molecules

Hydrogen bronzes can be used as hydrogen donors for the broad class of reactions involving proton-coupled electron transfer (PCET). Here, in this work, we describe a method to prepare platinum-decorated hydrogen tungsten bronzes, Pt@H x WO 3 · n H 2 O with n = 0, 1, and 2, by reacting the pristine oxides at modest temperatures with a mild reducing agent, H 3 PO 2 , and H 2 PtCl 6 in an aqueous solution. We explored the tunability and kinetics of this reaction and compared it with that of archetypal gas–solid hydrogen spillover. We demonstrate that the identity of the noble metal affects the extent of bronze reduction. This suggests that the mechanism proceeds via the adsorption of a hydrogen-atom species on the noble metal. Finally, we explored the ability of the Pt-decorated hydrogen tungsten bronzes to hydrogenate a model H + /e – acceptor, 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO). The bronze phases return to their fully oxidized states along with the subsequent reduction of TEMPO to TEMPOH. Overall, this work demonstrates a solution-phase method to obtain hydrogen bronzes, which can then be used to perform hydrogen transfer reactions, providing a pathway for the use of extended transition metal oxides as stoichiometric reagents for broad classes of hydrogenation reactions.

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

Breaking the passivation barrier via d-p orbital optimization for stable hydrogen production and sulfion upgrading

The development of energy-efficient hydrogen production technologies represents a critical pathway toward achieving global carbon neutrality objectives. This work provides fundamental insights into overcoming catalyst passivation challenges in sulfide oxidation reaction (SOR)-coupled hydrogen evolution reaction (HER) systems through precise orbital hybridization engineering. Our theoretical simulations reveal that sulfur-passivated ruthenium surfaces can effectively modulate d-p orbital hybridization, significantly reduce d-electron activity while stabilizing long-chain S 8 species and decreasing intermediate adsorption energies. Furthermore, metal carbides/ruthenium heterostructure (MC/Ru, M = V, Mo, W) was designed to achieve simultaneous optimization of both HER (∆G H* = −0.11 eV) and SOR (∆G RDS = 1.51 eV) via work-function-mediated interfacial electron transfer, which effectively tailors surface electronic states. Guided by theoretical predictions, we successfully synthesized a series of metal carbides/ruthenium/nitrogen-doped carbon catalysts based on a solid-phase reaction and designated as MC/Ru@NC (M = V, Mo, W). The optimized VC/Ru@NC catalyst exhibits exceptional performance in a membrane-free two-electrode system, achieving an ultralow cell voltage of 0.76 V at 200 mA cm −2 with outstanding stability over 1600 h, while maintaining 97.5 % Faradaic efficiency for hydrogen production and 73.8 % sulfur recovery efficiency.

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

Supercritical preparation of doped (111) facetted nickel oxide for the oxygen evolution reaction

Green hydrogen is of great interest as a replacement for traditional fossil fuels in a variety of energy applications. However, due to the poor kinetics present in the oxygen evolution reaction (OER) half-reaction, nanostructured catalysts are needed to reduce the reaction overpotential. Nickel oxide has previously been shown to be a promising alternative to expensive Pt-group based catalysts for the OER in alkaline media. Herein, facetted NiO nanosheets have been doped with Fe, Mn, or Co to reduce its catalytic overpotential for the OER. A supercritical synthesis process was used to promote the mass transport of the reactants while preserving catalytic surface area. Microscopy, diffraction, spectroscopy, and adsorption techniques were used to understand the morphological changes resulting from the inclusion of each dopant, as well as characterize the surface chemistry presented by the doped (111) facet. The pH was found to affect the properties of mixing due to difference in hydrolysis rates and catalysis of the hydrolysis/condensation. The dopants exhibited distinct effects on OER activity: Mn increased the overpotential to 742 mV vs. RHE, while Co and Fe reduced it to 502 mV and 457 mV, respectively. In summary, a straightforward and novel synthesis method is presented to prepare doped NiO(111) nanosheets, and their surface characteristics are explored to understand their varied electrochemical performances.

08 HYDROGEN↗
DOE OSTI2021

New Opportunity for Carbon-Supported Ni-based Electrocatalysts: Gas-Phase CO 2 Methanation

The cost-effectiveness and excellent performance of conductive-carbon-supported Ni-based electrocatalysts make them attractive materials for hydrogen oxidation and evolution reactions. However, they were previously unused in gas-phase hydrogenation reactions. In this work, we have expanded the applicability of commercially available advanced Ni/C, NiMo/C and NiRe/C materials from electrocatalysis to heterogeneous catalysis of CO 2 methanation. Our catalytic testing efforts indicate that the monometallic Ni/C material demonstrates the best CO 2 methanation properties, achieving an excellent CO 2 conversion of 83 % at 400 °C with nearly complete selectivity to CH 4 of 99.7 %, plus exhibiting intact performance during 90 h of time-on-stream testing. Such catalytic properties are among the highest reported to date among carbon-supported Ni-based methanation catalysts. Finally, excellent performance of Ni/C stems from the good dispersion of the Ni nanoparticles over N-containing carbon support material.

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

Investigating the non-classical M-H 2 bonding in OsClH 3 (PPh 3 ) 3

Dihydrogen ligation to metal centers results in a wide range of metal-hydrogen interactions. Compounds containing non-classical dihydrogen ligands in which the H-H contacts are significantly longer than the 0.74 A distance found in solid H 2 are classified as Kubas-like compounds, stretched dihydrogen ligands, or compressed dihydrides, depending on the H-H contact length. Compounds containing stretched dihydrogen and compressed dihydride ligands are somewhat rare. Developing a more complete understanding of the metal-hydrogen and hydrogen-hydrogen interactions in these species may provide insights into the mechanisms for the oxidative addition reaction and hydrogen storage. Here, we use diffraction and inelastic neutron scattering (INS) measurements, paired with both molecular and solid-state density functional theory (DFT), to fully characterize the nature of the metal-hydrogen and hydrogen-hydrogen interactions in a previously reported compound, OsClH 3 (PPh 3 ) 3 . In that report, the H-H distance was measured as 1.48(2) A by single-crystal neutron diffraction and was described as a "stretched" dihydrogen. The INS-generated phonon density of states is well described by the DFT calculations, including those normal modes dominated by the vibrational motions of the three Os-ligated hydrogen atoms. Additionally, the resulting calculated electron charge density landscape indicates that there is no remnant bonding character between the Os-ligated hydrogen atoms in the compound. Based on these findings, we update the understanding of the metal-hydrogen bonding in this complex and reclassify it as a compressed dihydride. As such, OsClH 3 (PPh 3 ) 3 represents a rare example of a non-classical compressed dihydride species.

08 HYDROGEN↗
DOE OSTI2023

Proton Relay for the Rate Enhancement of Electrochemical Hydrogen Reactions at Heterogeneous Interfaces

Proton transfer is critically important to many electrocatalytic reactions, and directed proton delivery could open new avenues for the design of electrocatalysts. However, although this approach has been successful in molecular electrocatalysis, proton transfer has not received the same attention in heterogeneous electrocatalyst design. Here, in this work, we report that a metal oxide proton relay can be built within heterogeneous electrocatalyst architectures and improves the kinetics of electrochemical hydrogen evolution and oxidation reactions. The volcano-type relationship between activity enhancement and pK a of amine additives confirms this improvement; we observe maximum rate enhancement when the pK a of a proton relay matches the pH of the electrolyte solution. Density-functional-theory-based reactivity studies reveal a decreased proton transfer energy barrier with a metal oxide proton relay. These findings demonstrate the possibility of controlling the proton delivery and enhancing the reaction kinetics by tuning the chemical properties and structures at heterogeneous interfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

PtRu Catalysts on Nitrogen-Doped Carbon Nanotubes with Conformal Hydrogenated TiO 2 Shells for Methanol Oxidation

The methanol oxidation reaction (MOR) is the limiting factor in direct methanol fuel cells (DMFC). There is an urgent need to improve the catalytic activity and stability of MOR catalysts. This study reports a highly active PtRu catalyst for MOR based on a hybrid multifunctional catalyst support consisting of a conformal amorphous hydrogenated TiO 2 shell wrapped around the oxygenated N-doped carbon nanotube core, denoted as PtRu/TiO 2 / ONCNT-400. Both the TiO 2 shell and the subsequent PtRu nanoparticles are deposited by a rapid microwave-assisted synthesis processes. The hydrogenated TiO 2 shell is found to exhibit a strong interaction with the deposited PtRu catalyst nanoparticles and effectively prevent them from agglomeration during the postdeposition thermal annealing to form more active crystalline PtRu alloy catalysts. In addition, the defective hydrogenated TiO 2 shell enhances the PtRu catalyst activity by the synergistic effects of partial charge transfer from TiO 2 to PtRu and high oxophilicity, which improves the kinetics of oxidation of poisonous CO intermediate to CO 2 . The mass activity for MOR and long-cycling stability of the PtRu/TiO 2 /ONCNT-400 catalyst surpass the two benchmark commercial PtRu/C catalysts from Johnson Matthey (JM) and Tanaka KiKinzoku (TKK), respectively. Furthermore, the results demonstrate that PtRu/TiO 2 /ONCNT-400 can serve as an efficient catalyst for MOR in DMFC.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Elucidating Hydrogen Reaction-Induced Water Desorption from Oxide-Passivated Metal Surfaces for Plasma Applications

Elucidating the mechanisms responsible for sub-microsecond desorption of water and other impurities from electrode surfaces at high heating rates is crucial for understanding pulsed power behavior. Ionization of desorbed impurities in the vacuum regions causes power or current loss; devising methods to limit such desorption during the short time scale of pulsed power is needed to improve corresponding applications. Previous molecular modeling studies have strongly suggested that, under high vacuum conditions, the amount of water impurity desorbing from oxide surfaces on metal electrodes is at a sub-monolayer level at room temperature, which appears insufficient to explain observed pulsed power energy losses at high current densities. In this work, we apply Density Functional Theory (DFT) techniques to show that hydrogen trapped inside iron metal can diffuse into hematite (α-Fe 2 O 3 ) on the metal surface, ultimately reacting with the oxide to form Fe(II) and H 2 O. The latter desorbs at elevated temperature and may explain the anomalous amount of desorbed impurity inferred from pulsed-power experiments. We also apply a suite of characterization techniques to demonstrate that when iron metal is heated to 650 °C, the dominant surface oxide component becomes α-Fe 2 O 3 . The oxide facets exposed are found to be a mixture of (0001), (10-10), and others, in agreement with the DFT models used.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

Understanding hydrogen electrocatalysis by probing the hydrogen-bond network of water at the electrified Pt–solution interface

Rational construction of the electrode–solution interface where electrochemical processes occur is of paramount importance in electrochemistry. Efforts to gain better control and understanding of the interface have been hindered by lack of probing methods. Here, in this study, we show that the hydrogen evolution and oxidation reactions (HER/HOR) catalysed by platinum in base can be promoted by introduction of N-methylimidazoles at the platinum–water interface. In situ spectroscopic characterization together with simulations indicate that the N-methylimidazoles facilitate diffusion of hydroxides across the interface by holding the second layer of water close to platinum surfaces, thereby promoting the HER/HOR. We thus propose that the HER/HOR kinetics of platinum in acid and base is governed by diffusion of protons and hydroxides, respectively, through the hydrogen-bond network of interfacial water by the Grotthuss mechanism. Moreover, we demonstrate a 40% performance improvement of an anion exchange membrane electrolyser by adding 1,2-dimethylimidazole into the alkali fed into its platinum cathode.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Targeted synthesis, characterization, and electrochemical analysis of transition-metal-oxide catalysts for the oxygen evolution reaction

Hydrogen fuel can be produced through the electrochemical splitting of water, an energy-intensive process that requires the use of electrocatalysts to be more efficient. Whereas current precious-metal-based electrocatalysts might be costly on a larger scale, transition-metal-oxide catalysts are more earth abundant and have shown promising activity. Here, the development and improvement of highly active transition-metal-oxide electrocatalysts is thus an important area of study where different catalyst enhancement strategies are used to drive the field forward. Additionally, transition-metal-oxide catalysts come in various different structures with their own advantages; thus, this review is focused on investigating the continuing field of transition-metal-oxide electrocatalysts of different structures and innovative methods of improving activity. By the end, new and promising paths forward in this field will be highlighted, particularly in the development of rock-salt oxides for the water-splitting system.

08 HYDROGEN↗
DOE OSTI2024

Revealing the role of redox reaction selectivity and mass transfer in current–voltage predictions for ensembles of photocatalysts

Photocatalysts are conceptually simple reaction units where nanoscale semiconductors integrated with catalysts drive a pair of redox reactions on illumination. However, the proximity of reaction sites performing cathodic and anodic reactions poses dire challenges to realize large light-to-fuel conversion efficiencies. In this study, a powerful, yet straightforward, equivalent-circuit detail-balance modeling framework is developed and applied to evaluate the performance of photocatalytic systems featuring multiple light absorbers. Specifically, low bandgap iridium-doped strontium titanate is modeled as a Z-scheme photocatalyst to achieve desirable hydrogen evolution and iron-based redox shuttle oxidation reactions. Our model has unique capabilities to simulate competing redox reactions and address mass-transfer limitations. In a significant departure from state-of-the-art circuit models, our study develops tools to perform load-line analyses by incorporating a net electrochemical load curve that includes both desired and competing redox reactions. Consequently, reaction selectivity is predicted from equivalent circuit models for photocatalytic and photoelectrochemical systems. Our investigation into ensembles comprised of multiple, semi-transparent light absorbers reveals their potential to outperform a single, optically thick light absorber, particularly when operated under mass-transfer-limited conditions. However, this outcome hinges on minimizing mass-transfer rates of select redox species to prevent undesired reactions of hydrogen oxidation and/or redox shuttle reduction. Our findings demonstrate that reaction selectivity can be achieved by tuning asymmetry in redox species mass-transfer even with perfectly symmetric electrocatalytic charge-transfer coefficients. The influences of various kinetic, mass-transfer, and thermodynamic parameters are explored to offer crucial insights for synthesis of the next-generation of photocatalysts and selective coatings, and reactor designs.

25 ENERGY STORAGE↗
DOE OSTI2026

Unveiling the mechanism of lithium-mediated nitrogen reduction via operando X-ray scattering in a flow cell with hydrogen oxidation

The lithium-mediated nitrogen reduction reaction (Li-NRR) is currently the most promising strategy for electrochemical ammonia synthesis. In this study, we present an operando grazing incidence wide angle X-ray scattering (GI WAXS) investigation using an improved electrochemical flow cell that enables hydrogen oxidation at the anode and thereby eliminates the need of a sacrificial proton donor. The improved cell design also increases nitrogen availability and mass transport, achieving ammonia faradaic efficiencies (FEs) up to 36%. This setup allows direct analysis of reaction intermediates and the solid electrolyte interphase (SEI) using state-of-the-art diglyme-based electrolytes. We identify lithium amide (LiNH2) as the only stable, crystalline intermediate, providing direct insight into the Li-NRR mechanism. Notably, in diglyme-based electrolytes, the SEI composition differs significantly from that in tetrahydrofuran-based systems, with reduced LiF content and the formation of previously unreported crystalline diglyme–lithium salt complexes. These species likely influence ammonia selectivity and long-term stability. Our findings highlight how the electrolyte composition and cell architecture govern Li-NRR selectivity and efficiency, offering a foundation for the rational design of next-generation SEI layers and solid electrolytes to enable scalable electrochemical ammonia synthesis.

Deissler, Niklas H. [Technical Univ. of Denmark, L↗
DOE OSTI2024

Oxide-Encapsulated Ruthenium Oxide Catalysts for Selective Oxygen Evolution in Unbuffered pH-Neutral Seawater

Direct seawater electrolysis is a promising approach to producing green hydrogen in water-scarce environments using renewable energy. However, the undesirable chlorine evolution reaction and hypochlorite evolution reaction compete with the desired oxygen evolution reaction (OER) at the anode electrocatalyst. This issue is most pronounced in unbuffered pH-neutral solutions due to local acidification resulting from the OER. To overcome this challenge, this study provides a comprehensive evaluation of the use of silicon oxide (SiO x ) and titanium oxide (TiO x ) nanoscale overlayers coated on metallic ruthenium (Ru) and ruthenium oxide (RuO x ) thin film electrodes and their ability to block chloride ions from reaching active sites during operation in an unbuffered 0.6 M NaCl electrolyte. Using a combination of (electro)analytical techniques, encapsulated RuO x anodes are shown to effectively suppress Cl - transport to buried catalyst active sites while allowing for the desired OER to occur, leading to increases in OER faradaic efficiency at moderate overpotentials. Evidence for the ability of SiO x overlayers to block Cl - ions from reaching the active buried interface was obtained by monitoring the ν(O-H) stretching mode of OH adsorbates using in situ Raman spectroscopy. Here, this study also reports trade-offs between the activity, selectivity, and stability of bare and encapsulated Ru and RuO x electrocatalysts, finding that the magnitude of these trade-offs strongly depends on the complex interplay between electrode architecture, material properties, and catalytic performance, especially in unbuffered pH-neutral seawater.

58 GEOSCIENCES↗
DOE OSTI2025

Development of Polycrystalline Photoelectrodes with Optimum Compositions and Morphologies for Solar Fuel Production via Electrochemical Synthesis (Final Technical Report)

Photoelectrochemical cells (PECs) can utilize solar energy for water splitting to produce H 2 as a clean fuel. The most critical components of a water-splitting PEC are semiconductor electrodes (photoelectrodes) that absorb solar energy to generate photoexcited charge carriers and transport them to the electrode/electrolyte interface for water reduction and oxidation reactions. While efficient PEC hydrogen production has been successfully demonstrated on the laboratory scale, the commercial viability of PECs depends critically on the cost of H 2 produced by the PECs, which is affected by the cost of PEC construction. Therefore, identifying promising inexpensive semiconductor electrodes is important. The goal of this project was to bring an advancement in the synthesis and understanding of inexpensive polycrystalline photoelectrodes based on oxides. Oxide-based semiconductors are inexpensive, easy to fabricate, and relatively more stable in aqueous media compared to other types of semiconductors. This project developed new electrodeposition methods to produce a variety of oxide-based semiconductor electrodes with precisely controlled compositions and morphologies to enhance photon absorption, electron-hole separation, and the use of electrons and holes for desired chemical reactions. The resulting high-quality photoelectrodes were investigated to establish the structure-composition-morphology-photoelectrochemical property relationships to identify the advantages and limitations of each oxide semiconductor system.

14 SOLAR ENERGY↗