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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Proton Conducting Silicon Oxide Membranes as a Fluorine Free Alternative to Nafion for Low Temperature Water Electrolysis

Driven by environmental and health concerns related to per- and polyfluoroalkyl substances (PFAS), there has been growing interest in developing fluorine-free proton (H + ) exchange membrane (PEM) materials for fuel cells and water electrolyzers. In this study, we present a side-by-side comparison of the key transport properties of submicron thick, PFAS-free amorphous silicon dioxide (SiO 2 ) membranes to Nafion, a fluorinated polymer electrolyte membrane that represents the industry standard for PEM fuel cells and electrolyzers. Here, measurements of proton (H + ) conductivity (σ H + ), hydrogen (H 2 ) permeability (P H 2 ), and electrical resistivity (ρ e – ) were conducted using model thin films comprised of SiO 2 membranes deposited by atomic layer deposition (ALD). Although the H + conductivity of the SiO 2 membranes is 2–3 orders of magnitude lower than Nafion, the addition of phosphorus dopants (PO x ) improves H + conductivity such that the area specific membrane resistance of thin (<50 nm) PO x -doped SiO 2 membranes is more than an order of magnitude lower than Nafion-117. Importantly, the safe operation of such nanoscale membranes within a PEM electrolyzer is feasible thanks to the low H 2 permeability of dense SiO 2 -based membranes, which are predicted to limit H 2 crossover rates to acceptable levels for pressures up to ≈ 100 bar. As a proof-of-principle demonstration, a chip-scale water electrolyzer based on 100 nm thick PO x -SiO 2 membrane is shown to achieve a current density of 2 A cm –2 at a potential of 2.5 V. If this technology can be successfully scaled up, H + conducting oxide membranes offer an attractive PFAS-free alternative to Nafion for efficient and durable water electrolysis and fuel cell technologies.

Nafion↗
DOE OSTI2026

Processing-Dependent Structure and Poroelasticity of Nafion in Liquid Water

Ionomers act as the solid polymer electrolyte membrane in many modern electrochemical devices, yet the role of their nanostructure in modulating the poroelastic response remains poorly understood, especially in liquid water, where few techniques can measure simultaneous transport-mechanical properties. Poroelastic Relaxation Indentation (PRI) is uniquely suited for measuring time-dependent transport-mechanical properties of porous solids, specifically hydraulic diffusivity, elastic modulus, Poisson’s ratio, and intrinsic permeability, for porous solids. While ionomers such as Nafion are not porous in the typical sense, Nafion has a nanophase-segregated structure that, when fully swollen in liquid water, behaves as a poroelastic solid with a coupled mechanical-transport response. Using a poroelastic framework, we investigate how casting and pretreatment of Nafion membranes alter their poroelastic response in liquid environments. We characterize both extruded and dispersion-cast Nafion membranes pretreated in water at 25 or 100 °C and relate the mechanical-transport properties to the ionomer structure via hydrophilic and intercrystalline domain spacing measured using Small-Angle X-ray Scattering (SAXS). At 25 °C, dispersion-cast membranes exhibit distinctly lower hydraulic diffusivity and intrinsic permeability than extruded membranes but with comparable mechanical properties. Pretreatment at 100 °C increases hydrophilic domain spacing, improving transport but at the expense of mechanical stiffness. Dispersion-cast membranes respond more strongly to pretreatment than extruded membranes. Using the Carman-Kozeny pore network model and the hydrophilic domain-spacing, we estimate the pore radius and tortuosity to show how pretreatment reduces structure-related tortuosity differences between dispersion-cast and extruded membranes. Here, in this work, we show that nanophase-segregated materials such as Nafion can be rigorously characterized using poroelasticity, resulting in physically meaningful transport-mechanical properties. Coupling PRI with SAXS provides insights into the nanostructural features that govern the coupled mechanical-transport response. By establishing PRI for a nanophase-segregated material, this approach opens avenues for this technique’s application in other hydrated polymeric materials not typically considered to be poroelastic.

Shen, Margaret [University of California, Berkeley↗
DOE OSTI2023

High-Temperature Rotating Disk Electrode Study of Platinum Bimetallic Catalysts in Phosphoric Acid

Understanding the H 3 PO 4 effect on the catalyst’s activity under a relevant condition is important for high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) catalyst research. Here, we report a high-temperature rotating disk electrode (HT-RDE) study of oxygen reduction reaction (ORR) in H 3 PO 4 . With the regular electrochemical protocol, we found that H 3 PO 4 reduction could occur during cyclic voltammetry study and form a reductive species—phosphorus acid (H 3 PO 3 ). Further, to obtain reliable ORR measurement, we optimized the protocol to avoid the H 3 PO 3 generation. The ORR activity of carbon-supported PtM (M = Fe, Co, Ni, Ru, Pd, and Ir) bimetallic alloy catalysts measured with this HT-RDE method showed higher ORR activity than Pt. To understand the alloying effect, we combine experiments in diluted solutions to distinguish the alloying effect on Pt–O binding and Pt–H 3 PO 4 binding. The results indicate that H 3 PO 4 mainly reduces available sites for ORR, with little effect on neighboring site’s Pt–O binding via Pt–H 3 PO 4 interaction, which is also supported by the density functional theory calculation of the Pt–O binding energy with/without H 2 PO 4 . Further study in a phosphoric acid-doped quaternary ammonium-biphosphate ion pair coordinated polyphenylene (PA-QAPOH) membrane electrode assembly (MEA) shows that the active alloy catalyst has better performance in both the HT-RDE and MEA. Also, the MEA gives higher ORR activity than the HT-RDE because of the higher pressure and less phosphoric acid content of the MEA. Yet, the gap between the HT-RDE and MEA is significantly smaller than that between the room temperature (RT)-RDE and MEA, suggesting the importance of temperature and H 3 PO 4 concentration in understanding ORR in HT-PEMFCs.

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

Membrane Strategies for Water Electrolysis

Hydrogen holds great promise as a clean energy resource to help the global carbon-free energy goal. Here, green hydrogen production from renewable energy-powered water electrolysis can decarbonize hard-to-abate industries and transport applications. Ion-exchange membranes are an essential component of membrane-based water electrolysis, enabling high hydrogen production efficiency through a zero-gap configuration. While perfluorosulfonic acids are the standard polymer electrolyte membrane material, research efforts for membrane alternatives have increased over the years to drive down the cost of electrolyzers and improve devices’ durability without sacrificing performance and efficiency. Here we present our perspectives on acidic, alkaline, and bipolar membranes for water electrolyzers and discuss future research directions to develop advanced membranes for green hydrogen production technology.

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

Fe–N–C Boosts the Stability of Supported Platinum Nanoparticles for Fuel Cells

The poor durability of Pt-based nanoparticles dispersed on carbon black is the challenge for the application of long-life polymer electrolyte fuel cells. Recent work suggests that Fe- and N-codoped carbon (Fe-N-C) might be a better support than conventional high-surface-area carbon. In this work, we find that the electrochemical surface area retention of Pt/Fe-N-C is much better than that of commercial Pt/C during potential cycling in both acidic and basic media. In situ inductively coupled plasma mass spectrometry studies indicate that the Pt dissolution rate of Pt/Fe-N-C is 3 times smaller than that of Pt/C during cycling. Density functional theory calculations further illustrate that the Fe-N-C substrate can provide strong and stable support to the Pt nanoparticles and alleviate the oxide formation by adjusting the electronic structure. The strong metal-substrate interaction, together with a lower metal dissolution rate and highly stable support, may be the reason for the significantly enhanced stability of Pt/Fe-N-C. In conclusion, this finding highlights the importance of carbon support selection to achieve a more durable Pt-based electrocatalyst for fuel cells.

25 ENERGY STORAGE↗
DOE OSTI2020

Scalable neutral H 2 O 2 electrosynthesis by platinum diphosphide nanocrystals by regulating oxygen reduction reaction pathways

Despite progress in small scale electrocatalytic production of hydrogen peroxide (H 2 O 2 ) using a rotating ring-disk electrode, further work is needed to develop a non-toxic, selective, and stable O 2 -to-H 2 O 2 electrocatalyst for realizing continuous on-site production of neutral hydrogen peroxide. We report ultrasmall and monodisperse colloidal PtP 2 nanocrystals that achieve H 2 O 2 production at near zero-overpotential with near unity H 2 O 2 selectivity at 0.27 V vs. RHE. Density functional theory calculations indicate that P promotes hydrogenation of OOH* to H 2 O 2 by weakening the Pt-OOH* bond and suppressing the dissociative OOH* to O* pathway. Atomic layer deposition of Al 2 O 3 prevents NC aggregation and enables application in a polymer electrolyte membrane fuel cell (PEMFC) with a maximum r(H 2 O 2 ) of 2.26 mmol h -1 cm -2 and a current efficiency of 78.8% even at a high current density of 150 mA cm -2 . Catalyst stability enables an accumulated neutral H 2 O 2 concentration in 600 mL of 3.0 wt% (pH = 6.6).

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

New roads and challenges for fuel cells in heavy-duty transportation

The recent release of hydrogen economy roadmaps for several major countries emphasizes the need for accelerated worldwide investment in research and development activities for hydrogen production, storage, infrastructure and utilization in transportation, industry and the electrical grid. Due to the high gravimetric energy density of hydrogen, the focus of technologies that utilize this fuel has recently shifted from light-duty automotive to heavy-duty vehicle applications. Decades of development of cost-effective and durable polymer electrolyte membrane fuel cells must now be leveraged to meet the increased efficiency and durability requirements of the heavy-duty vehicle market. This Review summarizes the latest market outlooks and targets for truck, bus, locomotive and marine applications. Required changes to the fuel-cell system and operating conditions for meeting Class 8 long-haul truck targets are presented. The necessary improvements in fuel-cell materials and integration are also discussed against the benchmark of current passenger fuel-cell electric vehicles.

08 HYDROGEN↗
DOE OSTI2020

Universal chemomechanical design rules for solid-ion conductors to prevent dendrite formation in lithium metal batteries

Dendrite formation during electrodeposition while charging lithium metal batteries compromises their safety. Although high-shear-modulus ( G s ) solid-ion conductors (SICs) have been prioritized to resolve the pressure-driven instabilities that lead to dendrite propagation and cell shorting, it is unclear whether these or alternatives are needed to guide uniform lithium electrodeposition, which is intrinsically density-driven. Here, we show that SICs can be designed within a universal chemomechanical paradigm to access either pressure-driven dendrite-blocking or density-driven dendrite-suppressing properties, but not both. This dichotomy reflects the competing influence of the SIC’s mechanical properties and the partial molar volume of Li + $(V_{\mathrm{Li}^+})$ relative to those of the lithium anode ( G Li and V Li ) on plating outcomes. Within this paradigm, we explore SICs in a previously unrecognized dendrite-suppressing regime that are concomitantly ‘soft’, as is typical of polymer electrolytes, but feature an atypically low $(V_{\mathrm{Li}^+})$ that is more reminiscent of ‘hard’ ceramics. Li plating (1 mA cm -2 ; T = 20 °C) mediated by these SICs is uniform, as revealed using synchrotron hard X-ray microtomography. As a result, cell cycle life is extended, even when assembled with thin Li anodes (~30 µm) and either high-voltage NMC-622 cathodes (1.44 mAh cm -2 ) or high-capacity sulfur cathodes (3.02 mAh cm -2 ).

25 ENERGY STORAGE↗
DOE OSTI2020

Selective Electrocatalysis Imparted by Metal-Insulator Transition for Durability Enhancement of Automotive Fuel Cells.

Repetitive start-up and shut-down events in polymer electrolyte membrane fuel cells for automotive applications lead to serious corrosion of the cathode due to an instantaneous potential jump that results from unintended air leakage into the anodic flow field followed by a parasitic oxygen reduction reaction (ORR) on the anode. Here we report a solution to the cathode corrosion issue during the start-up/shut-down events whereby intelligent catalyst design is used to selectively promote the hydrogen oxidation reaction (HOR) while concomitantly suppressing the ORR on the anode. Platinum thin layers supported on hydrogen tungsten bronze (Pt/HxWO3) suppressed the ORR by converting themselves into an insulator following exposure to oxygen, while selectively promoting the HOR by regaining metallic conductivity following subsequent exposure to hydrogen. The HOR-selective electrocatalysis imparted by a metal-insulator transition in Pt/HxWO3 demonstrated a remarkably enhanced durability of membrane electrode assemblies compared to those with commercial Pt/C catalysts.

Jung, Sang-Mun↗
DOE OSTI2022

Quantifying the electrochemical active site density of precious metal-free catalysts in situ in fuel cells

We report advances in the development of precious-group metal-free (PGM-free) catalysts for the oxygen reduction reaction (ORR) in fuel cell cathodes have produced active catalysts that reduce the performance gap to the incumbent Pt-based materials. However, utilization of state-of-the-art PGM-free catalysts for commercial applications is currently impeded by their relatively low durability. Methods designed to study catalyst degradation in the operation of fuel cells are therefore critical for understanding durability issues and, ultimately, their solutions. Here we report the use of Fourier-transform alternating current voltammetry as an electrochemical method for accurate quantification of the electrochemically active site density of PGM-free cathode catalysts, and to follow their degradation in situ during the operation of polymer electrolyte fuel cells. Using this method, we were able to quantify the electrochemical active site density, which will enable the elucidation of degradation mechanisms of PGM-free ORR catalysts in situ in fuel cells.

25 ENERGY STORAGE↗
DOE OSTI2026

Regulating in situ gaseous deposition to construct highly durable Fe–N–C oxygen-reduction fuel cell catalysts

The activity–stability trade-off challenges the design of high-performance atomically dispersed iron–nitrogen–carbon (Fe–N–C) catalysts for the acidic oxygen reduction reaction in polymer electrolyte fuel cells. Here we develop an in situ chemical vapour deposition approach during catalyst synthesis to break the trade-off, producing highly stable Fe–N–C catalysts while maintaining adequate oxygen reduction reaction activity. The optimal catalyst exhibits a half-wave potential of 0.867 V, remaining unchanged after an accelerated stress test (AST) of 100,000 potential cycles in rotating disk electrode tests. In membrane electrode assemblies under H 2 –air conditions, it delivers 93 mA cm −2 at 0.8 V after a standard AST of 30,000 voltage cycles, and shows minimal current density losses (2.9% at 0.6 V; 14.2% at 0.7 V) after an extended AST up to 120,000 cycles. Furthermore, the catalyst’s durability improvement is primarily due to the in situ chemical vapour deposition, which strengthens Fe–N bonds, increases active-site density, mitigates iron aggregates and reduces surface porosity.

Chemical engineering↗
DOE OSTI2020

Photo-driven growth of a monolayer of platinum spherical-nanocrowns uniformly coated on a membrane toward fuel cell applications

Membrane electrode assemblies (MEAs) serve as the core units of polymer electrolyte membrane fuel cells (PEMFCs) and are regularly fabricated by painting a slurry of commercial Pt/C onto a membrane, leading to thick and disordered electrocatalyst layers (CLs). Herein, we report a photo-driven fabrication of MEAs with ultra-thin and ordered CLs by growing a monolayer of dendritic platinum spherical nanocrowns onto each side of a photocatalyst-modified membrane. This approach allows us to control the thickness and platinum loading of ordered CLs by simply varying the concentration of the platinum precursor under tungsten light irradiation. The resultant MEAs exhibit an excellent fuel cell power density of 1.01 ± 0.05 W cm –2 at a platinum loading of 53 ± 1.5 μg cm cathode –2 . Furthermore, this exceptional activity likely arises from the nanostructured platinum crowns, efficient mass transport, and uniform reaction rate in the ultrathin (59 ± 12 nm thick) and ordered CLs according to electrochemical and theoretical investigations.

25 ENERGY STORAGE↗
DOE OSTI2022

A mechanistic study of the dopant-induced breakdown in halide perovskites using solid state energy storage devices

Doping halide perovskites (HPs) with extrinsic species, such as alkali metal ions, plays a critical, albeit often elusive role in optimising optoelectronic devices. Here, we use solid state lithium ion battery inspired devices with a polyethylene oxide-based polymer electrolyte to dope HPs controllably with lithium ions. We perform a suite of operando material analysis techniques while dynamically varying Li doping concentrations. We determine and quantify three doping regimes; a safe regime, with doping concentrations of <10 20 cm –3 (2% Li : Pb mol%) in which the HP may be modified without detrimental effect to its structure; a minor decomposition regime, in which the HP is partially transformed but remains the dominant species; and a major decomposition regime in which the perovskite is superseded by new phases. We provide a mechanistic description of the processes mediating between each stage and find evidence for metallic Pb (0) , LiBr and LiPbBr 2 as final decomposition products. Combining results from synchrotron X-ray diffraction measurements with in situ photoluminescence and optical reflection microscopy studies, we distinguish the influences of free charge carriers and intercalated lithium independently. We find that the charge density is equally as important as the geometric considerations of the dopant species and thereby provide a quantitative framework upon which the future design of doped-perovskite energy devices should be based.

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

Unraveling the core of fuel cell performance: engineering the ionomer/catalyst interface

The biggest obstacle to the widespread implementation of polymer electrolyte membrane fuel cells (PEMFCs) is their cost, primarily due to the use of platinum catalysts. The high intrinsic catalyst activity exhibited on a rotating disk electrode (RDE) is rarely realized in a membrane electrode assembly (MEA), which is a long-standing challenge for PEMFCs and a cause of low catalyst utilization. To translate the high RDE performance of a catalyst into a MEA, the design of an ideal ionomer/catalyst interface is proposed: a thin, conformal ionomer film covers the maximum surface of a Pt nanoparticle and thus simultaneously maximizes catalyst utilization, (i.e., high mass activity and electrochemically active surface area) and O 2 diffusion rate (i.e., high current density performance) without compromising proton conduction. Building such an interface is a long-standing challenge due to the lack of interaction between the ionomer and catalyst particles, resulting in large ionomer agglomerates and inhomogeneous ionomer coverage over the catalyst nanoparticle, with consequent poor fuel cell performance. In this work, this ionomer/catalyst interface has been engineered, utilizing the electrostatic attraction between positively charged catalyst and negatively charged ionomer particles in a catalyst ink and preserved in a solid catalyst layer. As a result, this interface leads to previously unachieved proton exchange membrane fuel cell performance in terms of both catalyst utilization (75% vs. 45%) and peak/rated power density (i.e., 1.430/0.930 W cm -2 , H 2 /air, cathode Pt loading: 0.1 mgPt cm -2 ) for pure Pt catalysts, even better than those of Pt alloy catalysts. This work demonstrates the formation of an interface in the liquid phase (using ultra-small-angle X-ray scattering in combination with cryo-TEM, isothermal–titration–calorimetry) and the preservation of the interface in the solid catalyst layer (using TEM) and estimates the effective coverage and thickness of the ionomer film (using limiting current density, RDE and fuel cell performance).

25 ENERGY STORAGE↗
DOE OSTI2022

Electronic structure manipulation via composition tuning for the development of highly conductive and acid-stable oxides

Exploring materials that simultaneously possess high conductivity and electrochemical stability is critical for various energy-conversion applications. In this study, our combined computations and experiments suggest the Mg–Ti–O chemical space for novel ternary oxide compounds offering high electrical conductivity and corrosion stability in acidic conditions to be potentially used as catalyst supporter of polymer electrolyte membrane fuel cells. High electrical conductivity (6.09 × 10 -1 S cm -1 ) is achieved at room temperature by tuning the chemical composition of Mg 1-x Ti 2+x O 5 while still maintaining good corrosion stability (1.2 × 10 -4 mA cm -2 after six days) in acidic conditions. Furthermore, we discover that a reducing gas environment during the synthesis increases the Ti solubility in Mg 1-x Ti 2+x O 5 with a reduced valence state of Ti, thus resulting in high conductivity.

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

Deconvoluting charge-transfer, mass transfer, and ohmic resistances in phosphonic acid–sulfonic acid ionomer binders used in electrochemical hydrogen pumps

Ion-pair high-temperature polymer electrolyte membranes (HT-PEMs) paired with phosphonic acid ionomer electrode binders have substantially improved the performance of HT-PEM electrochemical hydrogen pumps (EHPs) and fuel cells. Here, blending poly(pentafluorstyrene-co-tetrafluorostyrene phosphonic acid) (PTFSPA) with Nafion™, and using this blend as an electrode binder, improved proton conductivity in the electrode layer resulting in a 2 W cm –2 peak power density of fuel cells at 240 °C (a HT-PEM fuel cell record). However, much is unknown about how phosphonic acid ionomers blended with perfluorosulfonic acid materials affect electrode kinetics and gas transport in porous electrodes. In this work, we studied the proton conductivity, electrode kinetics, and gas transport resistances of 3 types of phosphonic acid ionomers, poly(vinyl phosphonic acid), poly(vinyl benzyl phosphonic acid), and PTFSPA by themselves and when blended with Aquivion® (a perfluorosulfonic acid material).

08 HYDROGEN↗
DOE OSTI2025

Challenges and strategies for probing the composite interface of PEM electrolyzers and fuel cells using operando AP-XPS

Left: cross-section schematic of a membrane electrode assembly, the working electrode changing state with applied potential. Center: the operando cell design that enables snapshot data acquisition during trajectory movement. Right: resulting spectra. Understanding the surface chemistry of electrocatalyst systems under operando conditions is central to revealing the electrocatalytic cell's working mechanisms. Determination of these catalytic processes on a molecular scale and the involved components is fundamental to streamlining material design for energy conversion and storage applications. X-ray photoelectron spectroscopy (XPS) is an established technique used to study the chemical and electronic states of materials. While the surface sensitivity of XPS is typically high, use of tender X-ray energies and technical advancements have allowed for the direct probing of solid–vapor and solid–liquid interfaces. However, protocols and documentation of experimental considerations for operando XPS probing of working electrolyzers and fuel cells remain scarce. Herein, we report an approach for the study of working polymer electrolyte membrane (PEM) electrolysis cells using ambient pressure X-ray photoelectron spectroscopy (AP-XPS). This approach directly probes the composite electrode surface on the membrane electrode assembly (MEA) in 100% relative humidity to establish a meaningful liquid layer for electrocatalysis. We carry out a systematic investigation from the cell constituent components to a fully assembled working operando electrolytic system and establish a method for AP-XPS study of the complex composite MEA, providing recommendations for data acquisition and component analysis.

Hamlyn, Rebecca↗
DOE OSTI2020

Modeling synergistic fuel cell membrane degradation with mitigating effects of cerium

During operation, polymer-electrolyte fuel cells undergo mechanical and chemical degradation, which behave synergistically and lead to accelerated membrane deterioration over time. This study builds upon previous modeling work on mechanical degradation, as described by a pinhole in the membrane, and chemical degradation mitigation by using cerium. By combining these two models, analysis can be carried out on the coupled degradation methods and how the mitigation effects of cerium disrupt the degradation cycle. The model results show how the presence of a pinhole in the membrane changes the distribution of cerium in the cell and modifies chemical degradation rates. In addition, the model shows how cerium affects the rate of pinhole growth by slowing down the rate of change in mechanical properties due to chemical degradation. Finally, the model shows how cerium modifies the mechanical and chemical degradation rates of the membrane under humidity- and voltage-cycling conditions.

Ehlinger, VM↗