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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Effects of Superparamagnetic Iron Nanoparticles on Electrocatalysts for the Reduction of Oxygen

It is of great research interest to understand the nanostructures contributing to the activity observed in the reduction of oxygen by non-platinum group metal (PGM) electrocatalysts in acidic media. Iron- and nitrogen-containing carbon networks are often the most studied structures, among which single-atom iron-coordinated nitrogen (FeNx) moieties have often been proposed to be the structures leading to the high activity in these non-PGM electrocatalysts. Iron nanoparticles embedded within a carbon support are also formed under certain conditions as a result of the synthetic processes in making non-PGM electrocatalysts. In this study, we present a study to understand the oxygen reduction reaction (ORR) activity of prepared iron- and nitrogen-containing non-PGM electrocatalysts obtained through the pyrolysis of metal–organic framework (MOF) precursors. We studied the structure–property relationship among nanostructures made from the MOF precursor ZIF-8 under different pyrolysis conditions. Density functional theory calculations were used to explain the effect of structural moieties on the ORR activity. Our results suggest that iron-coordinated C–N structures and iron nanoparticles act synergistically to catalyze the ORR.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Carbon flowers as electrocatalysts for the reduction of oxygen to hydrogen peroxide

Small-scale and decentralized production of H 2 O 2 via electrochemical reduction of oxygen is of great benefit, especially for sanitization, air and water purification, as well as for a variety of chemical processes. The development of low-cost and high-performance catalysts for this reaction remains a key challenge. Carbon-based materials have drawn substantial research efforts in recent years due to their advantageous properties, such as high chemical stability and high tunability in active sites and morphology. Deeper understanding of structure–activity relationships can guide the design of improved catalysts. We hypothesize that mass transport to active sites is of great importance, and herein we use carbon materials with unique flower-like superstructures to achieve high activity and selectivity for O 2 reduction to H 2 O 2 . The abundance of nitrogen active sites controlled by pyrolysis temperature resulted in high catalytic activity and selectivity for oxygen reduction reaction (ORR). The flower superstructure showed higher performance than the spherical nanoparticles due to greater accessibility to the active sites. Chemical activation improves the catalysts’ performances further, driving the production of H 2 O 2 to a record-setting rate of 816 mmol·g cat -1 ·h -1 using a bulk electrolysis setup. In conclusion, this work demonstrates the development of a highly active catalyst for the sustainable production of H 2 O 2 through rational design and synthetic control. The understanding from this work provides further insight into the design of future carbon-based electrocatalysts.

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

Characterization of Virgin, Re-used, and Oxygen-reduced Copper Powders processed by the Plasma Spheroidization Process

We report that fabrication of parts with high mechanical properties heavily depend on the quality of powder deployed in the fabrication process. Copper powder in three different powder types were spheroidized using radio-frequency inductively coupled plasma (ICP) spheroidization process (TekSphero-15 system). The characterized powders include virgin powder as purchased from the powder manufacturer, powder used in electron beam powder bed fusion (EB-PBF) process, and reconditioned powder, which was used powder that underwent an oxygen-reduction treatment. The goal of spheroidizing these powder types was to evaluate the change in powder morphology, the possibility of enhancing the powder properties back to their as-received conditions, and assess oxygen reduction of the powder lots given their initial oxygen contents. Also, to investigate the impact of re-spheroidization on powder properties, the second round of spheroidization was performed on the already used-spheroidized powder. The impact of powder type on powder sphericity and particle size distribution was evaluated using the image analysis of scanning electron microscope (SEM) micrographs and laser diffraction, respectively. The spheroidized powder showed higher sphericity and more uniform particle size distribution overall. Depending on the powder collection bin, second round of spheroidization affected the powder sphericity differently. The possibility of deploying the plasma spheroidization process as an alternative oxygen-reduction technique was also investigated through tracking the powders’ oxygen content using inert gas fusion method before and after the spheroidization. The plasma spheroidized powder showed less oxygen content than the hydrogen-treated powder. The second round of spheroidization caused no change in oxygen content. The correlation between oxygen-reduction and created cracks was discussed and compared between plasma spheroidization and hydrogen-treatment. The plasma spheroidization process created a powder with higher sphericity, uniform particle size, and less oxygen content.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

The origin of metallic conductivity in Pt 3 O 4 : a first principles study

The platinum oxide Pt 3 O 4 exhibits metallic conductivity even though it contains square-planar PtO4 units, which in related oxides such as PtO are usually associated with insulating behavior. To identify the electronic origin of this anomalous metallicity, we performed a comprehensive first-principles study using the PBE and r 2 SCAN functionals together with Hubbard U corrections and spin-orbit coupling (SOC). Structural benchmarks show that r 2 SCAN with SOC and a moderate U value (<4 eV) reproduces the experimental lattice constants and formation enthalpy, whereas larger U values (~8 eV) destabilize the cubic structure. Across all functionals and U values considered in this work, Pt 3 O 4 remains metallic. Analyses of the projected density of states, band structures, charge-density isosurfaces, and bonding characteristics demonstrate that the dominant contribution to the metallic character originates from delocalized Pt–O–Pt hybridized antibonding states at the Fermi level. Direct Pt–Pt interactions are present but contribute less strongly to the conductivity. Bader charge analysis reveals only weak Pt charge disproportionation, consistent with mixed Pt II /Pt III character, and a small charge-transfer energy that prevents localization of the Pt 5d electrons even at elevated U. In contrast, PtO develops a Mott or charge-transfer gap under modest U despite having the same PtO 4 coordination environment. These findings demonstrate that persistent Pt–O–Pt covalency is the primary driver of metallicity in Pt 3 O 4 and support the view that this phase can remain conductive under oxygen reduction and oxygen evolution reaction conditions in fuel cell and electrolyzer environments.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Baselining Activity and Stability of ORR Catalysts and Electrodes for Proton Exchange Membrane Fuel Cells for Heavy-Duty Applications

Activity and stability of electrodes with Pt and PtCo alloy catalysts supported on high surface area carbon, hereafter to as a-Pt/C and d-PtCo/C, were evaluated for heavy-duty applications. Both catalysts had nearly identical Pt loading (50-wt% Pt on carbon and 0.25 mg Pt cm −2 ) and had undergone thermal treatment to stabilize them by growing the average particle size to 4–5 nm. Both were subjected to 90,000 (90 k) standard accelerated stress tests (AST) cycles consisting of 0.6–0.95 V square wave potentials, 3-s hold at upper and lower potential limits in H 2 /N 2 at 1.5 atm, 80 °C and 100% RH. Test protocols were developed to monitor the performance losses and characterize them in terms of activity for the oxygen reduction reaction (ORR), oxygen transport in the electrode and proton transport in the membrane and cathode catalyst layer. Despite the nearly double initial ORR activity, the PtCo/C electrode degraded faster due to the leaching of Co from the catalyst that had started even before the imposition of the AST potential cycles. Commensurate with Co leaching, Co poisoning of ionomer is responsible for the inferior performance of d-PtCo/C electrode at high current densities both before and after AST.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2024

Corrosion-Resistant Non-Carbon Electrocatalyst Supports for PEFCS

Insufficient durability of commercial catalysts is a persistent issue for PEFC applications.1 Herein, Pt on Nb-doped-TiO 2 is reported as a highly durable electrocatalyst on which the direct 4-electron reduction of oxygen to water is more facile compared to Pt/C. All performance metrics are reported comparing Pt/Nb-TiO2 with a 15% Pt loading, against a commercial Pt/C catalyst (46.5% Pt loading, Tanaka, K. K.). Nb-doped-TiO 2 with high surface area and high electronic conductivity was synthesized using the supercritical fluid method. Initially, the durability of the catalyst was characterized using accelerated stability tests (ASTs) involving 10,000 high potential cycles (DOE/FCCJ protocol) and the Pt/Nb-TiO 2 was found to retain 78% of its initial electrochemically active surface area (ECSA) compared to the 57.6 % retained by Pt/C. These observations were in excellent agreement with previous reports that the Pt particle size of Pt/C grew from 2nm to 8nm during the AST protocol along with severe corrosion and amorphization of the carbon surface.2, 3 TEM and XPS studies of the Pt-Nb-doped-TiO 2 catalyst showed that the Pt particle size grew from 3nm to 6nm and the Nb(IV) and Ti(III) in the support were oxidized to Nb(V) and Ti(IV) after the durability test. Thus, the improvement in Pt/Nb-TiO 2 ECSA retention was attributed to the lower extent of particle growth and lack of oxidative support loss upon oxidation as compared to Pt/C. The oxygen reduction reaction (ORR) performance was characterized by linear polarization using a rotating disk electrode (RDE). The electrochemical surface areas of Pt/Nb-TiO 2 and Pt/C were found to be 48m2·g -1 and 83m2·g -1 respectively, and the mass activity for the ORR at 0.9V vs. RHE were found to be 150 mA·mg-1Pt and 124 mA·mg-1Pt respectively. The improved mass activity on Pt/Nb-TiO 2 was attributed to strong metal support interaction (SMSI) between the Nb-TiO 2 support and the Pt catalyst based on the 625 meV decrease in the binding energy of the Pt4f x-ray photo-electron spectroscopy (XPS) peaks of Pt/Nb-TiO 2 compared to Pt/C. To quantify the impact of the SMSI, a kinetic model was applied to calculate the elementary reaction rate constants for the various steps of the ORR on both catalysts. The reaction rate constant (k1) for the direct 4-electron transfer pathway to produce H 2 O was significantly larger in Pt/Nb-TiO 2 as compared to Pt/C. Thus, the reduction in the electron binding energy as observed in the XPS was found to aid the facile filling of the higher energy 2p orbitals of O 2 thereby leading to improved 4-electron transfer kinetics and improved overall activity.

08 HYDROGEN↗
DOE OSTI2020

Surface Charge and Electrostatic Spin Crossover Effects in CoN 4 Electrocatalysts

Carbon materials doped with nitrogen and 3d transition metals have attracted a great deal of interest for catalyzing electrochemical reactions such as water splitting, oxygen reduction, and carbon dioxide reduction. Here, we employed density functional theory to study Co–N-doped carbon as electrocatalysts for the oxygen reduction and oxygen evolution reactions. Specifically, we investigated the interplay among adsorption energies, the spin state of the CoN 4 active center, and the applied potential. We found that adsorption energies strongly depend on both the applied potential and the spin state of the Co center. Furthermore, spin state transitions induced by the applied potential also play an important role in determining the adsorption energies. Here, this effect originates from a different potential of zero charge and capacitance of each spin state.

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

Porous FeCo Glassy Alloy as Bifunctional Support for High-Performance Zn-Air Battery

Zn-air battery (ZAB) is attracting increasing attention due to its high safety and performance. However, the practical application of ZAB relies heavily on developing durable support materials to replace conventional carbon supports which have unrecoverable corrosion issues, severely jeopardizing ZAB performance. Herein, a novel porous FeCo glassy alloy was developed as bifunctional catalytic support for ZAB. Specifically, the conducting skeleton of the porous glassy alloy was used to stabilize oxygen reduction cocatalysts, and more importantly, the FeCo served as the primary phase for oxygen evolution. To prove the concept of catalytic glassy alloy support, ultra-small Pd nanoparticles were anchored, as oxygen reduction active sites, on the porous FeCo (noted as Pd/FeCo) for ZAB. The Pd/FeCo exhibited a significantly improved electrocatalytic activity for oxygen reduction (a half-wave potential of 0.85 V) and oxygen evolution (a potential of 1.55 V to reach 10 mA cm –2 ) in the alkaline media. When used in the ZAB, the Pd/FeCo delivered an output power density of 117 mW cm –2 and outstanding cycling stability for over 200 h (400 cycles), surpassing the conventional carbon-supported Pt/C+IrO 2 catalysts. Such an integrated design of combining highly active components with porous architecture provides a new strategy to develop novel nanostructured electrocatalysts.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Toward Superb Perovskite Oxide Electrocatalysts: Engineering of Coupled Nanocomposites

Abstract A significant issue that bedeviled the commercialization of renewable energy technologies, ranging from low‐temperature water electrolyzers to high‐temperature solid oxide cells, is the lack of high‐performance catalysts. Among various candidates that could tackle such a challenge, perovskite oxides are rising‐star materials because of their unique structural and compositional flexibility. However, single‐phase perovskite oxides are challenging to satisfy all the requirements of electrocatalysts concurrently for practical applications, such as high catalytic activity, excellent stability, good ionic and electronic conductivities, and superior chemical/thermo‐mechanical robustness. Impressively, perovskite oxides with coupled nanocomposites are emerging as a novel form offering multifunctionality due to their intrinsic features, including infinite interfaces with solid interaction, tunable compositions, flexible configurations, and maximum synergistic effects between assorted components. Considering this new configuration has attracted great attention owing to its promising performances in various energy‐related applications, this review timely summarizes the leading‐edge development of perovskite oxide‐based coupled nanocomposites. Their state‐of‐art synthetic strategies are surveyed and highlighted, their unique structural advantages are highlighted and illustrated through the typical oxygen reduction reaction and oxygen evolution reactions in both high and low‐temperature applications. Opinions on the current critical scientific issues and opportunities in this burgeoning research field are all provided.

08 HYDROGEN↗
DOE OSTI2024

Graphene-supported single atom catalysts for high performance lithium-oxygen batteries

The optimal choice of d-block metals in single atom catalysts (SACs) is crucial for designing efficient electrocatalysts for activating the Oxygen reduction reaction (ORR)/ Oxygen evolution reaction (OER) in lithiumoxygen batteries (LOBs). Herein, we used the Quantum Mechanics methods to understand the origin of reactivity for a series of 16 d-block metals supported on nitrogen-doped graphene as SACs for ORR and OER in LOBs. Based on the Gibbs free energy calculations, we found that among the 16 SACs investigated, Zn-SAC exhibits the highest electrochemical activity with the lowest overpotential of 0.17 V. Here we then used machine learning (ML) to develop an intrinsic descriptor, phi, that correlates the catalytic activity with electronic and chemical properties of the catalytic centers at the M-N 4 active site on graphene surface. We established a linear relationship between phi and the catalytic activity that provides guidance for designing efficient SACs for electrocatalysis in LOBs. To validate these predictions, we report electrochemical measurements showing that Zn-SAC exhibits an ultra-stable cyclability with reduced overpotentials over Mo-SAC and nitrogen-doped graphene (NG), confirming our theoretical prediction. This fundamental work provides a deep understanding on the rational design of efficient SACs for OER/ ORR in LOBs.

25 ENERGY STORAGE↗
DOE OSTI2020

Performance enhancement and degradation mechanism identification of a single-atom Co–N–C catalyst for proton exchange membrane fuel cells

Development of platinum group metal (PGM)-free catalysts for oxygen reduction reaction (ORR) has been a strategic research topic for proton exchange membrane (PEM) fuel cells. Present state-of-art PGM-free ORR catalysts are Fe, N co-doped carbon (Fe-N-C) catalysts, which unfortunately exhibit instability concerns. Herein, we report a stable atomically dispersed Co, N co-doped carbon (Co-N-C) catalyst with high Co content of 1.0 at% and the active site, i.e., the coordination of Co, is CoN2+2 in nature. The Co-N-C catalyst demonstrated high ORR activity comparable to, and high stability over 3 times better than, that of the Fe-N-C catalyst. It also achieved a high activity of 22 mA cm2 at 0.9 ViR-free and a power density of 0.61 W cm-2 under 1.0 bar H2/O2. Further, we identify two main degradation mechanisms of the PGM-free catalysts: catalyst oxidation by H2O2/radicals and demetalation. The improved stability of Co-N-C relative to Fe-N-C is attributed to less Fenton-reactive nature of Co and significantly enhanced resistance to demetalation of Co-N-C.

Xie, Xiaohong↗
NASA NTRS1983

Electrocatalysis of fuel cell reactions: Investigation of alternate electrolytes

Oxygen reduction and transport properties of the electrolyte in the phosphoric acid fuel cell are studied. A theoretical expression for the rotating ring-disk electrode technique; the intermediate reaction rate constants for oxygen reduction on platinum in phosphoric acid electrolyte; oxygen reduction mechanism in trifluoromethanesulfonic acid (TFMSA), considered as an alternate electrolyte for the acid fuel cells; and transport properties of the phosphoric acid electrolyte at high concentrations and temperatures are covered.

Chin, D. T.↗
DOE OSTI2020

The effect of water vapor on surface oxygen exchange kinetics of thin film (La,Sr)(Co,Fe)O 3-δ

Oxygen reduction and transport in electrochemical applications are strongly affected by the reactant gas composition, including impurities such as water. Understanding the relationship between oxygen reactivity and humidity is key for attaining stability and high efficiency of solid oxide fuel cells, which are especially attractive for transportation applications as low emission power generation devices. Both short- and long-term effects of moisture have previously been associated with use of ambient air. To better understand these effects, we study oxygen exchange kinetics at the cathode surface and the cathode/electrolyte interface using La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) epitaxial thin films as a model-surface system. In situ synchrotron X-ray techniques evaluate the oxygen reduction reaction (ORR) kinetics in response to environmental variables. The results suggest a clear enhancement of the ORR rate upon short term exposure of the perovskite-structured films to water. Finally, on the basis of these measurements, along with in situ X-ray characterization of Sr segregation and computational first-principles studies, we suggest a model for this increased ORR activity that may lead to further improvements by stabilizing active cathode surface configurations.

25 ENERGY STORAGE↗
NASA NTRS1984

Electrocatalysis of fuel cell reactions: Investigation of alternate electrolytes

Oxygen reduction and transport properties of the electrolyte in the phosphoric acid fuel cell are studied. The areas covered were: (1) development of a theoretical expression for the rotating ring disk electrode technique; (2) determination of the intermediate reaction rate constants for oxygen reduction on platinum in phosphoric acid electrolyte; (3) determination of oxygen reduction mechanism in trifluoreomethanesulfonic acid (TFMSA) which was considered as an alternate electrolyte for the acid fuel cells; and (4) the measurement of transport properties of the phosphoric acid electrolyte at high concentrations and temperatures.

Chin, D. T.↗
DOE OSTI2020

Direct insights into the role of epoxy groups on cobalt sites for acidic H 2 O 2 production

Hydrogen peroxide produced by electrochemical oxygen reduction reaction provides a potentially cost effective and energy efficient alternative to the industrial anthraquinone process. In this study, we demonstrate that by modulating the oxygen functional groups near the atomically dispersed cobalt sites with proper electrochemical/chemical treatments, a highly active and selective oxygen reduction process for hydrogen peroxide production can be obtained in acidic electrolyte, showing a negligible amount of onset overpotential and nearly 100% selectivity within a wide range of applied potentials. Combined spectroscopic results reveal that the exceptionally enhanced performance of hydrogen peroxide generation originates from the presence of epoxy groups near the Co–N 4 centers, which has resulted in the modification of the electronic structure of the cobalt atoms. Computational modeling demonstrates these electronically modified cobalt atoms will enhance the hydrogen peroxide productivity during oxygen reduction reaction in acid, providing insights into the design of electroactive materials for effective peroxide production.<

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗