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All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

How Selective Transport Layer Improves Efficiency and Durability of Proton Exchange Membrane Fuel Cells

In any electrochemical device, the separator or membrane allows specific ions to transport but blocks electrons and other chemical species, enabling the electrochemical energy to be harvested. However, small amounts of undesired species are known to permeate through the membrane, reducing overall system efficiency and lifetime. An emerging concept called the “Selective Transport Layer” preferentially allows only protons to pass through but reduces the permeance of other species by a meaningful degree. Here, in this study, we demonstrate that a 60 nm thick graphene oxide composite layer can be very effective in reducing gas and ion permeation, even for a gas as small as H 2 , while not noticeably increasing proton transport resistance. In electrode and membrane accelerated stability tests, we show that both electrode and membrane durability are improved by a factor of two. Microscopy and mathematic simulations confirm that the graphene oxide composite is effective in blocking transport of dissolved Pt 2+ . The improved durability and reduced H 2 fuel crossover are expected to substantially reduce initial and operating costs of the fuel cell system. How this technology may affect other membrane-based electrochemical devices is also discussed.

Ngo, Phuong Quynh [General Motors, Pontiac, MI (Un↗
DOE OSTI2018

Development of a Simple and Rapid Diagnostic Method for Polymer-Electrolyte Fuel Cells

A simple and fast diagnostic tool has been developed for analyzing polymer-electrolyte fuel-cell degradation. The tool is based on analyzing changes in polarization curves of a cell over its lifetime. The shape of the polarization-change curve and its sensitivity to oxygen concentration are found to be unique for each degradation pathway based on analysis from a detailed 2-D numerical model of the cell. Using the polarization-change curve methodology, the primary mechanism for degradation (kinetic, ohmic, and/or transport related) can be identified. Here, the technique is applied to two sets of data to explain performance changes after two different cells undergo voltage-cycling accelerated stress test, where it is found that changes are kinetic and then ohmic or transport in nature depending on the cell type. The diagnostic tool provides a simple method for rapid determination of primary degradation mechanisms. Finally, areas for more detailed future investigations are also summarized.

08 HYDROGEN↗
DOE OSTI2017

Thermochemical Stability Study of Alkyl-Tethered Quaternary Ammonium Cations for Anion Exchange Membrane Fuel Cells

The increased interest in the use of anion exchange membranes (AEMs) for applications in electrochemical devices has prompted significant efforts in designing materials with robust stability in alkaline media. Most reported AEMs suffer from polymer backbone degradation as well as cation functional group degradation. In this report, we provide comprehensive experimental investigations for the analysis of cation functional group stability under alkaline media. A silver oxide-mediated ion exchange method and an accelerated stability test in aqueous KOH solutions at elevated temperatures using a Parr reactor were used to evaluate a broad scope of quaternary ammonium (QA) cationic model compound structures, particularly focusing on alkyl-tethered cations. Additionally, byproduct analysis was employed to gain better understanding of degradation pathways and trends of alkaline stability. Experimental results under different conditions gave consistent trends in the order of cation stability of various QA small molecule model compounds. Overall, cations that are benzyl-substituted or that are near to electronegative atoms (such as oxygen) degrade faster in alkaline media in comparison to alkyl-tethered QAs. These comprehensive model compound stability studies provide valuable information regarding the relative stability of various cation structures and can help guide researchers towards designing new and promising candidates for AEM materials.

25 ENERGY STORAGE↗
DOE OSTI2013

A Semi-Empirical Two Step Carbon Corrosion Reaction Model in PEM Fuel Cells

The cathode CL of a polymer electrolyte membrane fuel cell (PEMFC) was exposed to high potentials, 1.0 to 1.4 V versus a reversible hydrogen electrode (RHE), that are typically encountered during start up/shut down operation. While both platinum dissolution and carbon corrosion occurred, the carbon corrosion effects were isolated and modeled. The presented model separates the carbon corrosion process into two reaction steps; (1) oxidation of the carbon surface to carbon-oxygen groups, and (2) further corrosion of the oxidized surface to carbon dioxide/monoxide. To oxidize and corrode the cathode catalyst carbon support, the CL was subjected to an accelerated stress test cycled the potential from 0.6 VRHE to an upper potential limit (UPL) ranging from 0.9 to 1.4 VRHE at varying dwell times. The reaction rate constants and specific capacitances of carbon and platinum were fitted by evaluating the double layer capacitance (Cdl) trends. Carbon surface oxidation increased the Cdl due to increased specific capacitance for carbon surfaces with carbon-oxygen groups, while the second corrosion reaction decreased the Cdl due to loss of the overall carbon surface area. The first oxidation step differed between carbon types, while both reaction rate constants were found to have a dependency on UPL, temperature, and gas relative humidity.

08 HYDROGEN↗
DOE OSTI2016

Polybenzimidazole (PBI) functionalized nanographene as highly stable catalyst support for polymer Electrolyte membrane fuel cells (PEMFCs)

Nanoscale graphenes were used as cathode catalyst supports in proton exchange membrane fuel cells (PEMFCs). Surface-initiated polymerization that covalently bonds polybenzimidazole (PBI) polymer on the surface of graphene supports enables the uniform distribution of the Pt nanoparticles, as well as allows the sealing of the unterminated carbon bonds usually present on the edge of graphene from the chemical reduction of graphene oxide. The nanographene effectively shortens the length of channels and pores for O 2 diffusion/water dissipation and significantly increases the primary pore volume. Further addition of p-phenyl sulfonic functional graphitic carbon particles as spacers, increases the specific volume of the secondary pores and greatly improves O 2 mass transport within the catalyst layers. The developed composite cathode catalyst of Pt/PBI-nanographene (50 wt%) + SO 3 H-graphitic carbon black demonstrates a higher beginning of life (BOL) PEMFC performance as compared to both Pt/PBI-nanographene (50 wt%) and Pt/PBI-graphene (50 wt%) + SO 3 H-graphitic carbon black (GCB). Accelerated stress tests show excellent support durability compared to that of traditional Pt/Vulcan XC72 catalysts, when subjected to 10,000 cycles from 1.0 V to 1.5 V. As a result, this study suggests the promise of using PBI-nanographene + SO 3 H-GCB hybrid supports in fuel cells to achieve the 2020 DOE targets for transportation applications.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2017

PERLE – BEAM OPTICS DESIGN

PERLE (Powerful ERL for Experiments) [1] is a novel ERL test facility, initially proposed to validate design choices for a 60 GeV ERL needed for a future extension of the LHC towards a hadron-electron collider, the LHeC [2]. Its main goal is to test the limits of a high current, CW, multi-pass operation with superconducting cavities at 802 MHz (and perhaps exploring other frequencies of interest). PERLE optics features Flexible Momentum Compaction (FMC) lattice architecture for six vertically stacked return arcs and a high current, 5 MeV photo-injector. With only one pair of 4-cavity cryomodules, 400 MeV beam energy can be reached in three re-circulation passes, with beam currents in excess of 15 mA. This unique quality beam is intended to perform a number of experiments in different fields reaching from uncharted tests of accelerator components via elastic ep scattering to laser-Compton backscattering for photon physics [3]. Following the experiment, the CW beam is decelerated in three consecutive passes back to the injection energy, transferring virtually stored energy back to the RF.

Bogacz, S.↗
DOE OSTI2021

Beam Profile Measurements Utilizing an Amplitude Modulated Pulsed Fiber Laser at PIP2IT

Fermilab is undertaking the development of a new 800 MeV superconducting RF linac to replace its present normal conducting 400 MeV linac. The PIP-II linac consists of a warm front-end generating 2 mA of 2.1 MeV H⁻ followed immediately by a series of superconducting RF cryomodules to 800 MeV. To limit the potential damage to the superconducting RF cavities, PIP-II will utilize laser-based monitors to obtain beam profiles via photoionization. This paper will present the results of transverse and longitudinal beam profile measurements using a prototype profile monitor that was tested with 2.1 MeV H⁻ beam at the PIP-II Injector Test (PIP2IT) accelerator. This prototype profile monitor utilizes a high repetition rate fiber laser and fiber optic transport into the PIP2IT enclosure. In addition, results will be shown of narrow-band electron detection from amplitude modulated laser pulses.

43 PARTICLE ACCELERATORS↗
DOE OSTI2018

Update on Plasma Processing R&D for LCLS-II

SRF cavities performance preservation is crucial, from vertical test to accelerator operation. Field emission is still one of the main problems to overcome and plasma cleaning has been proven successful by SNS, in cleaning field emitters and increasing the work function of Nb. A collaboration has been established between FNAL, SLAC and ORNL with the purpose of applying plasma processing to LCLS-II cavities, in order to minimize and overcome field emission without affecting the high Q of N-doped cavities. The recipe will follow the neon-oxygen active plasma adopted at SNS, allowing in-situ processing of cavities and cryomodules from hydrocarbon contaminants. A novel method for plasma ignition has been developed at FNAL: a plasma glow discharge is ignited using high order modes to overcome limitations imposed by the fundamental power coupler. The results of experiments on 9-cell LCLS-II cavity are presented, along with plasma ignition studies. In addition the RF system is shown and N-doped Nb samples studies are discussed.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

Impact of Solenoid Induced Residual Magnetic Fields on The Prototype SSR1 CM Performance

A prototype cryomodule containing eight Single Spoke Resonators type-1 (SSR1) operating at 325 MHz and four superconducting focusing lenses was successfully assembled, cold tested, and accelerated beam in the framework of the PIP-II project at Fermilab. The impact of induced residual magnetic fields from the solenoids on performance of cavities is presented in this contribution. In addition, design optimizations for the production cryomodules as a result of this impact are highlighted.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

Sulfur poisoning mechanism of LSCF cathode material in the presence of SO 2 : a computational and experimental study

Aiming at the comprehensive understanding of the single sulfur poisoning effect and, eventually, the multiple impurities poisoning phenomena on the SOFC (Solid Oxide Fuel Cell) cathode materials, the sulfur poisoning effect on the (La 0.6 Sr 0.4 ) 0.95 Co 0.2 Fe 0.8 O 3 (LSCF-6428) has been investigated in the presence of 10 ppm SO 2 at 800, 900, and 1000°C, respectively, with a combined computational and experimental approach. The good agreement between the CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) simulations and the XRD (X-Ray Diffraction), SEM (Scanning Electron Microscopy), and TEM (Transmission Electron Microscopy) characterization results support the reliability of the CALPHAD approach in the SOFC field. Furthermore, comprehensive simulations were made to understand the impact of temperature, P(SO 2 ), P(O 2 ), and Sr concentration on the threshold of SrSO 4 stability. Results showed that the formation of SrSO4 is thermodynamically favored at lower temperatures, higher P(SO 2 ), higher P(O 2 ), and higher Sr concentration. Finally, comparisons were also made between LSCF-6428 and LSM20 (La 0.8 Sr 0.2 MnO 3 ) using simulations, which confirmed that LSCF-6428 is a poor sulfur-tolerant cathode, in agreement with the literature.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Kinetics of Chronic Oxidation of NBG-17 Nuclear Graphite by Water Vapor

This report presents the results of kinetic measurements during accelerated oxidation tests of NBG-17 nuclear graphite by low concentration of water vapor and hydrogen in ultra-high purity helium. The objective is to determine the parameters in the Langmuir-Hinshelwood (L-H) equation describing the oxidation kinetics of nuclear graphite in the helium coolant of high temperature gas-cooled reactors (HTGR). Although the helium coolant chemistry is strictly controlled during normal operating conditions, trace amounts of moisture (predictably < 0.2 ppm) cannot be avoided. Prolonged exposure of graphite components to water vapor at high temperature will cause very slow (chronic) oxidation over the lifetime of graphite components. This behavior must be understood and predicted for the design and safe operation of gas-cooled nuclear reactors. The results reported here show that, in general, oxidation by water of graphite NBG-17 obeys the L-H mechanism, previously documented for other graphite grades. However, the characteristic kinetic parameters that best describe oxidation rates measured for graphite NBG-17 are different than those reported previously for grades H-451 (General Atomics, 1978) and PCEA (ORNL, 2013). In some specific conditions, certain deviations from the generally accepted L-H model were observed for graphite NBG-17. This graphite is manufactured in Germany by SGL Carbon Group and is a possible candidate for the fuel elements and reflector blocks of HTGR.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2016

Status of Chronic Oxidation Studies of Graphite

Graphite will undergo extremely slow, but continuous oxidation by traces of moisture that will be present, albeit at very low levels, in the helium coolant of HTGR. This chronic oxidation may cause degradation of mechanical strength and thermal properties of graphite components if a porous oxidation layer penetrates deep enough in the bulk of graphite components during the lifetime of the reactor. The current research on graphite chronic oxidation is motivated by the acute need to understand the behavior of each graphite grade during prolonged exposure to high temperature chemical attack by moisture. The goal is to provide the elements needed to develop predictive models for long-time oxidation behavior of graphite components in the cooling helium of HTGR. The tasks derived from this goal are: (1) Oxidation rate measurements in order to determine and validate a comprehensive kinetic model suitable for prediction of intrinsic oxidation rates as a function of temperature and oxidant gas composition; (2) Characterization of effective diffusivity of water vapor in the graphite pore system in order to account for the in-pore transport of moisture; and (3) Development and validation of a predictive model for the penetration depth of the oxidized layer, in order to assess the risk of oxidation caused damage of particular graphite grades after prolonged exposure to the environment of helium coolant in HTGR. The most important and most time consuming of these tasks is the measurement of oxidation rates in accelerated oxidation tests (but still under kinetic control) and the development of a reliable kinetic model. This report summarizes the status of chronic oxidation studies on graphite, and then focuses on model development activities, progress of kinetic measurements, validation of results, and improvement of the kinetic models. Analysis of current and past results obtained with three grades of showed that the classical Langmuir-Hinshelwood model cannot reproduce all data collected so far. Starting from here we propose a modification of the LH model to include temperature activation of graphite surface as a Boltzmann activation function. The enhanced Boltzmann-Langmuir-Hinshelwood model (BLH) was tested successfully on three grades of graphite. The model is a robust, comprehensive mathematical function that allows better fitting of experimental results spanning a wide range of temperature and partial pressures of water vapor and hydrogen. However, the model did not fit satisfactorily the data extracted from the old report on graphite H-451 oxidation by water.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Materials and Designs for High-Efficacy LED Light Engines

Cree, Inc. conducted a narrow-band downconverter (NBD) materials development and implementation program which will lead to warm-white LED light engines with enhanced efficacy via improved spectral efficiency with respect to the human eye response. New red (600-630nm) NBD materials could result in as much as a 20% improvement in warm-white efficacy at high color quality relative to conventional phosphor-based light sources. Key program innovations included: high quantum yield; narrow peak width; minimized component-level losses due to “cross-talk” and light scattering among red and yellow-green downconverters; and improved reliability to reach parity with conventional phosphors. NBD-enabled downconversion efficiency gains relative to conventional phosphors yielded an end-of-project LED light engine efficacy of >160 lm/W at room temperature and 35 A/cm2, with a correlated color temperature (CCT) of ~3500K and >90 CRI (Color Rending Index). NBD-LED light engines exhibited equivalent luminous flux and color point maintenance at >1,000 hrs. of highly accelerated reliability testing as conventional phosphor LEDs. A demonstration luminaire utilizing an NBD-based LED light engine had a steady-state system efficacy of >150 lm/W at ~3500K and >90 CRI, which exceeded the 2014 DOE R&D Plan luminaire milestone for FY17 of >150 lm/W at just 80 CRI.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2017

New Fuel Cell Membranes with Improved Durability and Performance

The objective of this project was to meet all the DOE Fuel Cell Technologies Office Multi-Year Research, Development and Demonstration Plan for membrane performance, durability and cost targets simultaneously with a single membrane. The approach was to develop new proton exchange membranes, integrate them into membrane electrode assemblies (MEA’s) and then evaluate them in single fuel cells and finally fuel cell stacks. These membranes were based on Multi Acid Side Chain (MASC) ionomers containing stabilizing additives and reinforced with electrospun nanofibers. The ionomers developed at 3M are based on a fluorinated polymer with side chains that contain one or more sulfonamide groups and a sulfonic acid group. Both of these groups facilitate proton transport and ionomers were made that show exceptional conductivity, especially at hot and dry conditions. At the same time, 3M and Vanderbilt University developed new mechanical support technology based on electrospun nanofibers. The membranes made by combining the new ionomers and nanofiber supports were evaluated at 3M and General Motors and met all the DOE technical targets except for one; the resistance at 120°C and 40 kPa water vapor pressure. A detailed analysis of the membrane requirements needed to meet this target was completed.The DOE cost target was evaluated internally but not publicly disclosed. In the final year of the project a durability issue was identified with the sulfonimide link in the MASC polymer. Accelerated durability testing revealed a decay in performance along with an increase in membrane resistance. And, despite the fact that all but one of DOE technical targets and both Go/No Go milestones were met in the fourth and eight quarters, the membranes developed in this project could not pass the final project milestone of 2,000 hours testing in an automotive fuel cell stack at GM. Work in the final year focused on understanding the nature of the ionomer stability. New test methods were employed such as multilayer membrane tests that allowed for detailed analysis of membranes at the end of life. Model compound studies of small molecules were initiated to investigate the stability of the sulfonimide and other functional groups present in the ionomer. At the conclusion of the project, an effective strategy to improve the ionomer stability has yet to be identified. Despite the setback with the ionomer stability, this project has demonstrated significant advances in the field of fluorinated proton exchange membranes for automotive and other applications. The concept of multi-acid side chain ionomers had proven to be an effective strategy to reduce membrane resistance and electrospun nanofibers proven to be a viable mechanical support technology. We intend to build on these results in future membrane development efforts.

08 HYDROGEN↗
DOE OSTI2018

Compositionally Graded Alloy Quantum Dot Phosphors for Solid State Lighting. Final Report

To push the boundaries of efficiency and cost in solid state lighting (SSL), narrow band red emitting down conversion phosphors must be improved. These materials are critical to both the color rendering ability and optical output of phosphor converted light emitting diodes (LEDs). Improvements in these performance parameters will have a significant impact on the adoption of SSL in retail, office, and home lighting applications. Quantum Dots (QDs) are widely acknowledged as a cost-effective front-runner among developing downconverting technologies because they emit narrow band luminescence that is tunable across the visible spectrum. Current syntheses of quantum dots, however, utilize expensive and toxic reagents and often involve several time-intensive purification steps. To address this, we have introduced a novel, cost-effective synthetic scheme, whereby the final quantum dot structures can be accessed with fewer synthetic steps using a library of inexpensive, easily-synthesized precursors. With the help of automated high throughput synthesis robotics, Columbia, LBNL, and OSRAM have optimized red and amber CdS/CdSe/CdS QD architectures for SSL. QDs with improved shelling layers have been identified that meet the industry state of the art performance on chip under high humidity accelerated aging tests. This is remarkable considering the time frame of this project compared to the time and resources allocated for the development of the industrial standard. Furthermore, although particle stability to optical charging is often stressed in improving QLED performance, we have identified effective ZnS particle over-coating as the most important factor determining particle survivability and device performance in down-converting LEDs.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Low RF Power Plasma Ignition and Detection for In-Situ Cleaning of 1.3 GHz 9-Cell Cavities

Superconducting Radio Frequency (SRF) cavities performance preservation is crucial, from vertical test to accelerator operation. Field Emission (FE) is still one of the performance limiting factors to overcome and plasma cleaning has been proven successful by the Spallation Neutron Source (SNS), in cleaning field emitters and increasing the work function of Nb. A collaboration has been established between Fermi National Accelerator Laboratory (FNAL), SLAC National Accelerator Lab- oratory and Oak Ridge National Laboratory (ORNL) with the purpose of applying plasma processing to the Linac Coherent Light Source-II (LCLS-II) cavities, in order to minimize and overcome field emission without affecting the high Q of nitrogen-doped cavities. The cleaning for LCLS-II will follow the same plasma composition adopted at SNS, which allows in-situ processing of cavities installed in cryomod-ules from hydrocarbon contaminants. A novel method for plasma ignition has been developed at FNAL: a plasma glow discharge is ignited using high order modes to overcome limitations imposed by the fundamental power coupler, allowing in-situ cleaning for cavities in cryomodule. The plasma can be easily ignited and tuned in each of the cavity cells using low RF power. A method for plasma detection has been developed as well, which allows the detection of the plasma location in the cavity without the need of cameras at both cavity ends. The presented method can be applied to other multi-cell cavity designs, even for accelerators where the coupling for the fundamental modes at room temperature is very weak.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

Validation of Wichner Predictive Model for Chronic Oxidation by Moisture of Nuclear Graphite

This document reports the results of multi-year extensive research on chronic oxidation of nuclear graphite by traces of moisture that might be present in the helium coolant of high-temperature gas-cooled reactors (HTGRs). The research focuses on four grades of nuclear graphite that are considered potential candidates for component fabrication in advanced nuclear reactors. The four grades are (1) PCEA (medium-fine grain, extruded, manufactured by GrafTech Inc., USA); (2) NBG-17 (medium-fine grain, vibrationally molded, manufactured by SGL Carbon, Germany/France); (3) IG-110 (microfine grain, isostatically molded, manufactured by Toyo Tanso, Japan); and (4) 2114 (microfine grain, isostatically pressed, manufactured by Mersen, USA). The experimental part of this research comprised three objectives that were consistently pursued for each graphite material: (1) accelerated oxidation tests in well-controlled conditions (temperature, gas composition) and analysis of chemical kinetic models and of their parameters for each graphite grade; (2) measurements of water vapor transport rates from H 2 O/He mixtures through thin graphite slabs for estimation of the water effective diffusivity specific to each material; (3) controlled oxidation of graphite specimens in H 2 O/He mixtures and characterization of the effects of oxidation temperatures on the density profiles of oxidized layers. These three groups of experimental results were interpreted using the model developed by Wichner et al. for predicting the penetration depth of oxidants (moisture or oxygen) as a function of oxidation conditions. Basically, starting from the kinetic and transport properties of each graphite grade, the ultimate goal was predicting the stable density profile in the oxidized layer and its dependence on the oxidation temperature. The profiles obtained this way were then compared against direct observations of oxidized layers in specimens obtained in well-controlled oxidation conditions. The general agreement between predictions and observations validated the general applicability of the Wichner model. The results obtained in this project were presented at annual Department of Energy–Advanced Reactor Technologies program reviews and at specialist meetings and conferences and were published in Oak Ridge National Laboratory (ORNL) reports and in professional journals. The results published in 2018 had an immediate impact in 2019, when a group from three US universities used ORNL kinetic data as input information in a complex simulation of chronic oxidation by moisture using the same graphite grades during long-time operation in a modular high-temperature gas-cooled reactor. Their conclusion, in line with the conclusions obtained at the end of this project, was that chronic graphite oxidation by moisture during normal operation conditions of an HTGR will be limited to a thin surface layer of graphite blocks at the reactor bottom, where the highest temperatures are. That will not affect the integrity of graphite components and reactor safety, provided the impurity concentration in the helium coolant is rigorously controlled and maintained at the design specifications.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗