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At least 721 records · Page 40

All sources NASA NTRS DOE OSTI

DOE OSTI2025

Structure of iridium oxide catalysts dictates performance differences for proton exchange membrane water electrolyzers

Proton exchange membrane water electrolyzers (PEMWEs) are promising zero-emission technologies. However, their high cost remains a barrier to widespread adoption. Iridium oxide is commonly used as an oxygen evolution reaction (OER) catalyst, and its cost and scarcity make it essential to reduce its loading while increasing its activity. Evaluation of iridium oxide activity should be carried out in the membrane electrode assembly (MEA) configuration to replicate realistic operating conditions. Herein, we present a comprehensive benchmarking framework to accurately evaluate the amorphous and crystalline iridium oxides at the MEA level. By systematically varying the catalyst loading, this study confirmed that each MEA was utilized uniformly, presenting intrinsic electrochemical properties independent of the loading. Through intrinsic charge density determined by voltammetry, we established two electrochemical descriptors to evaluate catalyst redox reactions. The mass activity was evaluated by correlating current vs. loading, and the slope provides loading-independent mass activity. The effect of the porous transport layer on OER activity was discussed, identifying a ‘background’ current at zero-loading. In conclusion, this study highlights potential pitfalls in MEA-level catalyst screening and underscores the importance of the loading study for reliable results.

Kwon, Obeen [University of California, Irvine, CA ↗

DOE OSTI2022

Exsolution-Driven Surface Transformation in the Host Oxide

Exsolution synthesizes self-assembled metal nanoparticle catalysts via phase precipitation. An overlooked aspect in this method thus far is how exsolution affects the host oxide surface chemistry and structure. Such information is critical as the oxide itself can also contribute to the overall catalytic activity. Here, combining X-ray and electron probes, we investigated the surface transformation of thin-film SrTi 0.65 Fe 0.35 O 3 during Fe 0 exsolution. We found that exsolution generates a highly Fe-deficient near-surface layer of about 2 nm thick. Moreover, the originally single-crystalline oxide near-surface region became partially polycrystalline after exsolution. Such drastic transformations at the surface of the oxide are important because the exsolution-induced nonstoichiometry and grain boundaries can alter the oxide ion transport and oxygen exchange kinetics and, hence, the catalytic activity toward water splitting or hydrogen oxidation reactions. These findings highlight the need to consider the exsolved oxide surface, in addition to the metal nanoparticles, in designing the exsolved nanocatalysts.

36 MATERIALS SCIENCE↗

NASA NTRS2000

Process and Equipment for Nitrogen Oxide Waste Conversion to Fertilizer

The present invention describes a process for converting vapor streams from sources containing at least one nitrogen-containing oxidizing agent therein to a liquid fertilizer composition comprising the steps of: (1) directing a vapor stream containing at least nitrogen-containing oxidizing agent to a first contact zone; (2) contacting said vapor stream with water to form nitrogen oxide(s) from said at least one nitrogen- containing oxidizing agent; (3) directing said acid(s) as a second stream to a second contact zone; (4) exposing said second stream to hydrogen peroxide which is present within said second contact zone in a relative amount of at least 0.1% by weight of said second stream within said second contact zone to convert at least some of any nitrogen oxide species or ions other than in the nitrite form present within said second stream to nitrate ion; (5) sampling said stream within said second contact zone to determine the relative amount of hydrogen peroxide within said second contact zone; (6) adding hydrogen peroxide to said second contact zone when a level on hydrogen peroxide less than 0.1% by weight in said second stream is determined by said sampling; (7) adding a solution comprising potassium hydroxide to said second stream to maintain a pH between 6.0 and 11.0 within said second stream within said second contact zone to form a solution of potassium nitrate; and (8) removing sais solution of potassium nitrate from said second contact zone.

Lueck, Dale E.↗

NASA NTRS2003

Process for Nitrogen Oxide Waste Conversion to Fertilizer

The present invention describes a process for converting vapor streams from sources containing at least one nitrogen-containing oxidizing agent therein to a liquid fertilizer composition comprising the steps of: a) directing a vapor stream containing at least one nitrogen-containing oxidizing agent to a first contact zone; b) contacting said vapor stream with water to form nitrogen oxide(s) from said at least one nitrogen-containing oxidizing agent; c) directing said acid(s) as a second stream to a second contact zone; d) exposing said second stream to hydrogen peroxide which is present within said second contact zone in a relative amount of at least 0.1% by weight of said second stream within said second contact zone to convert at least some of any nitrogen oxide species or ions other than in the nitrate form present within said second stream to nitrate ion; e) sampling said stream within said second contact zone to determine the relative amount of hydrogen peroxide within said second contact zone; f) adding hydrogen peroxide to said second contact zone when a level of hydrogen peroxide less than 0.1 % by weight in said second stream is determined by said sampling; g) adding a solution comprising potassium hydroxide to said second stream to maintain a pH between 6.0 and 11.0 within said second stream within said second contact zone to form a solution of potassium nitrate; and h) removing said solution of potassium nitrate from said second contact zone.

Lueck, Dale E.↗

DOE OSTI2025

Importance of hydrogen oxidation reaction current in quantifying hydrogen crossover in PEM water electrolyzers at high differential pressure

Understanding hydrogen permeation in proton exchange membrane water electrolyzers (PEMWEs) operating at high differential pressures (>25 bar) is critical towards developing effective gas recombination strategies that enable safe operation and high efficiency. Developing this understanding relies on accurate quantification of hydrogen crossover rates in water electrolyzers operating under such conditions. In this work, we show that PEMWEs operating at high differential pressures exhibit noticeable hydrogen oxidation reaction (HOR) currents. As the HOR consumes part of the permeated hydrogen at the anode, neglecting HOR currents leads to severe underestimation of the hydrogen crossover rate. We implemented a new method combining hydrogen oxidation current with online gas chromatography measurements to accurately quantify hydrogen crossover rates as a function of operating current density in PEMWEs operating at high differential pressures (10–30 bar g ).

25 ENERGY STORAGE↗

DOE OSTI2021

Crack Stability in Breached Fuel

This report describes the fracture mechanics formalism to evaluate the stability of cracks in a fuel cladding. Recognized consensus-body linear elastic fracture mechanics (LEFM) was applied to identify the crack instability length, or the length at which unstable mechanical crack extension would occur, as a function of pellet swelling loading (radial strain and fraction conversion from UO 2 to U 3 O 8 ) at the local cracked cladding region for two postulated fracture toughness (K IC ) values of the cladding. The crack opening displacement (COD) and the crack opening area (COA) were also identified. This analysis informs evaluations for crack extension and the potential for pellet debris loss from the fuel rod for cases of pellet oxidation in dry storage canisters where inadvertent residual water may undergo radiolysis causing oxidizing conditions to pellets exposed to the canister environment through breached cladding.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

DOE OSTI2021

Crack Stability in Breached Fuel

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2024

High-Temperature Oxidation Behavior of Wrought and Additive Manufactured Alloys in Direct-Fired Supercritical CO2 Power Cycle Environments

Materials selection is a key concern for corrosion resistance in elevated temperature and pressure direct-fired supercritical CO2 (sCO2) power cycles. The effect of elevated pressure on corrosion resistance can be critical, as impurities within the supercritical fluid such as H2O and O2 can have additional corrosion effects than found at ambient pressure conditions. Several wrought nickel-based commercial alloys (230, 263, 282, 617, 625, 740H) were exposed to direct-fired conditions (95CO2 – 4H2O – 1 O2) at 750 °C at both atmospheric pressure (0.1 MPa) and supercritical conditions (20 MPa) for over 2,000 h. Additionally, additive manufactured (AM) 282 produced by laser powder bed fusion (LPBF) were also included in the exposures. Supercritical conditions affected the oxidation behavior of several alloys. Most notably, water-vapor assisted Cr-oxide volatilization was observed at 750 °C supercritical conditions. Many alloys did not form sufficient protective Cr-oxide scales at supercritical conditions, leading to increased oxidation at elevated pressure. Differences in oxidation behavior were also observed for 282 AM samples compared to their wrought counterparts, with the differences also dependent on the LPBF build parameters and post-production treatments (heat treatment and surface finishing procedures). The AM samples formed Mo-rich carbides in the alloy beneath the oxide following sCO2 exposure, implying potentially higher levels of carbon uptake relative to the wrought

Carney, Casey↗

NASA NTRS2002

High Temperature Corrosion of Silicon Carbide and Silicon Nitride in Water Vapor

Silicon carbide (SiC) and silicon nitride (Si3N4) are proposed for applications in high temperature combustion environments containing water vapor. Both SiC and Si3N4 react with water vapor to form a silica (SiO2) scale. It is therefore important to understand the durability of SiC, Si3N4 and SiO2 in water vapor. Thermogravimetric analyses, furnace exposures and burner rig results were obtained for these materials in water vapor at temperatures between 1100 and 1450 C and water vapor partial pressures ranging from 0.1 to 3.1 atm. First, the oxidation of SiC and Si3N4 in water vapor is considered. The parabolic kinetic rate law, rate dependence on water vapor partial pressure, and oxidation mechanism are discussed. Second, the volatilization of silica to form Si(OH)4(g) is examined. Mass spectrometric results, the linear kinetic rate law and a volatilization model based on diffusion through a gas boundary layer are discussed. Finally, the combined oxidation and volatilization reactions, which occur when SiC or Si3N4 are exposed in a water vapor-containing environment, are presented. Both experimental evidence and a model for the paralinear kinetic rate law are shown for these simultaneous oxidation and volatilization reactions.

Opila, E. J.↗

DOE OSTI2020

Effect of ionizing radiation on PuO2 and surrogate oxide materials under storage conditions

The stockpile of plutonium separated from used nuclear fuel amounts to many 100s of tonnes. The majority of this plutonium is stored as PuO2 powder packaged in multi-can containers. The conditions during the packaging of reprocessed PuO2 for long term storage are closely controlled to limit water uptake as radiolytic decomposition of any adsorbed water will lead to the formation of both a potentially flammable atmosphere containing molecular hydrogen as well as reactive oxygen species which may be incorporated into the oxide phase. Consequently, the safety case for the long-term storage of PuO2 requires a complete understanding of the fundamental physical, chemical and materials degradation processes occurring at the water-oxide interface inside the storage canisters. This study investigates the effect of ionizing radiation on PuO2 and various surrogate oxides under atmospheres potentially encountered in storage canisters.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2026

Molecularly engineered ZnO–carbon nanosheets from fumaric acid precursors for efficient photocatalytic water purification

The photocatalytic breakdown of organic contaminants is crucial for the development of water purification technology. Zinc oxide (ZnO) is an extensively researched photocatalyst; however, its efficacy is hindered by rapid charge recombination and limited utilization of UV irradiation. Resolving these issues necessitates integrating ZnO with conductive carbon phases via scalable, low-temperature synthesis. We provide a molecularly designed sol–gel method that converts zinc–fumarate coordination networks into two-dimensional ZnO–carbon nanosheets utilizing solely aqueous precursors and mild annealing temperatures (400–600 °C). This method utilizes fumaric acid as a dicarboxylate linker and polyvinylpyrrolidone (PVP) as a structural carbon source to produce ultrathin wurtzite ZnO nanosheets embedded inside an amorphous carbon matrix. The resultant ZnO-C hybrid achieves nearly complete methylene blue degradation within 10 min under UV-A illumination, demonstrating first-order kinetics and outstanding recyclability. Compared with commercial ZnO, the ZnO–C nanosheets exhibit comparable rapid photocatalytic degradation, enhanced adsorption behavior, a porous nanosheet morphology, and an integrated ZnO–carbon interfacial structure. These findings provide a viable molecular-templating approach to fabricating various metal oxide–carbon photocatalysts and underscore substantial enhancements in semiconductor efficacy in eco-friendly water treatment systems.

Ozcan, Muca [ORNL] (ORCID:0000000320020474)↗

DOE OSTI2026

Enabling Long Term, Shelf‐Stable Perovskite Solar Cells: Alumina Barriers to Protect Perovskite Devices from Moisture and Oxygen

Current encapsulation architectures for thin-film metal halide perovskite do not adequately eliminate all ambient stressors. Here, we develop low transmission rate barrier layers using atomic layer deposited (ALD) aluminum oxide grown directly on the completed photovoltaic (PV) device stack to provide an additional seal, prior to full packaging. We investigate the effect of deposition temperature and oxidant chemistries on the barrier growth for protection of perovskite photovoltaic devices. We characterize the layers individually, then integrate into devices to detail the tradeoff between protection and deposition compatibility. To enhance compatibility and impermeability, we present an approach using water as the aluminum oxidant during nucleation and switching from water to ozone for the remainder of the growth. At 50 nm, the barrier results in a water vapor transmission rate (WVTR) of 4.5·10 −4 g/m 2 /day, and 1,000-hour device stability under 45°C with 85% relative humidity without further packaging. This barrier provides sufficient protection to enable minimal degradation of the perovskite solar cells while completely submerged in water for 140 minutes. Additionally, we characterize the oxygen transmission rate (OTR) to be 0.49 cm 3 /m 2 /day at 23°C and 0% relative humidity, which is 1.5 orders of magnitude improvement over the OTR of the current encapsulation.

14 SOLAR ENERGY↗

DOE OSTI2023

2023 American Society for Mass Spectrometry (ASMS) 71st Annual Conference on Mass Spectrometry and Allied Topics

Title (20 words): The investigation of the mechanism for the water splitting by holmium oxide nitrate complex in gas-phase Introduction (120 words): The studies for hydrogen from water splitting is important for clean energy economy as molecular hydrogen is a potential energy carrier. Therefore, understanding the fundamental chemistry of water splitting is essential. The water splitting activated by [Ho(NO3)4]- was previously studied. The suggested mechanism was to first eliminate •NO2 from [Ho(NO3)4]- to make [HoO(NO3)3]-. Then, water was added to form [HoO(NO3)3(H2O)]-, followed by eliminating the •OH to form [HoOH(NO3)3]-. However, we proposed a new mechanism with the formation of [Ho(NO3)3]- prior to the water addition. Once water is added to this intermediate to make [Ho(NO3)3(H2O)]-, the •H is eliminated to form [HoOH(NO3)3]-. Here we have used a labeled experiments with 18-O nitrates. The results to support the new mechanism are discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Phenomenology of Intermediate Molecular Dynamics at Metal-Oxide Interfaces

Reaction intermediates buried within a solid-liquid interface are difficult targets for physiochemical measurements. They are inherently molecular and locally dynamic, while their surroundings are extended by a periodic lattice on one side and the solvent dielectric on the other. Challenges compound on a metal-oxide surface of varied sites and especially so at its aqueous interface of many prominent reactions. Recently, phenomenological theory coupled with optical spectroscopy has become a more prominent tool for isolating the intermediates and their molecular dynamics. The following article reviews three examples of the SrTiO3-aqueous interface subject to the oxygen evolution from water: reaction-dependent component analyses of time-resolved intermediates, a Fano resonance of a mode at the metal-oxide–water interface, and reaction isotherms of metastable intermediates. The phenomenology uses parameters to encase what is unknown at a microscopic level to then circumscribe the clear and macroscopically tuned trends seen in the spectroscopic data.

Chemistry↗

DOE OSTI2021

Achieving Stable Molybdenum Oxide Cathodes for Aqueous Zinc‐Ion Batteries in Water‐in‐Salt Electrolyte

Abstract Layered MoO 3 represents a promising cathode for aqueous rechargeable Zn‐ion batteries, but the implementation of this material is limited due to the low conductivity and poor structural stability. A 30 m ZnCl 2 water‐in‐salt electrolyte (WISE) is introduced to a MoO 3 nanobelt cathode for the first time, significantly increasing the stability of MoO 3 cathodes compared to those in 3 m ZnSO 4 and 3 m ZnCl 2 . The Zn/MoO 3 cell in WISE unambiguously demonstrate significantly improved rate performance delivering 349, 253, and 222 mAh g −1 at 100, 500, and 1000 mA g −1 , denoting a 12× capacity increase of those achieved in 3 m electrolytes at 1000 mA g −1 . A capacity retention rate of 73% is achieved after (dis)charging at 100 mA g −1 for 100 cycles, and no obvious capacity fading is observed at higher current densities of 500 mA g −1 and 2 A g −1 . Specifically, the data suggest that the drastic fading in 3 m electrolytes can be attributed to the parasitic surface deposits on Zn originated from Mo dissolution and H 2 formation due to Zn corrosion and hydrogen evolution reaction, which are significantly suppressed in the WISE. The direct visualization of these side reactions is achieved for the first time in the Zn‐MoO 3 system, using an in situ optoelectrochemical measurement.

Wang, Lei↗

DOE OSTI2024

Morphological analysis of iridium oxide anode catalyst layers for proton exchange membrane water electrolysis using high-resolution imaging

Not Available

08 HYDROGEN↗

DOE OSTI2022

La–Sr–Co oxide catalysts for oxygen evolution reaction in anion exchange membrane water electrolyzer: The role of electrode fabrication on performance and durability

Anion exchange membrane water electrolysis is an attractive technology for low-cost generation of “green” hydrogen by combining the use of noble metal-free catalysts with pure water feed. By thus addressing main drawbacks of the liquid alkaline electrolysis and proton exchange membrane water electrolysis, anion exchange membrane water electrolysis stands an excellent chance of replacing the two technologies. The development of active and stable platinum group metal (PGM)-free catalysts for oxygen evolution reaction (OER) is crucial for making anion exchange membrane water electrolyzers (AEMWEs) practical. For this work, we synthesized, characterized and tested two La–Sr–Co oxide-based OER catalysts. First, we characterized the catalysts by XRD, SEM, and N 2 physisorption and assessed their OER activity in a three-electrode cell. Next, we focused on electrode fabrication, demonstrating the importance of catalyst-ink application to the porous transport layers (PTLs) and a key role of adding a binder to the catalyst ink to prevent the catalyst detachment from the PTL in pure water. We tested three membrane electrode assemblies prepared using different formulations of the anode catalyst ink. The results show that the optimum ink formulation is essential for the performance on pure-water feed by maximizing OH - conductivity of the catalyst layer and catalyst-membrane interface.

47 OTHER INSTRUMENTATION↗

DOE OSTI2021

Effect of Water Vapor on Lifetime of 625 and 120 Foils During Oxidation Between 650 and 800 °C

In this work, the oxidation behavior of alloy 625 and 120 foils was studied at 650, 700 and 800 °C in dry air and flowing air + 10% H 2 O up to 10,000 h (alloy 625) or 30,000 h (alloy 120). The effect of water vapor on Cr loss was investigated. Manganese and iron in the 120 foil induced faster Cr depletion in the foil and breakdown of the Cr 2 O 3 scale into Fe and Cr-rich oxide compared to the alloy 625 foil. In the latter case, the presence of Nb led to the formation of Nb and Cr-rich oxide after breakdown of the Cr 2 O 3 scale. Simultaneous Cr loss due to oxidation and volatilization of the Cr 2 O 3 oxide scale was predicted and compared to experimental Cr loss measurements for exposures up to 30,000 h.

36 MATERIALS SCIENCE↗