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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Meso-Structured Polymer Electrolyte Fuel Cell Electrode

Increasing the utilization of Pt and Pt alloy catalysts in polymer electrolyte fuel cell cathodes is critical to improving the high power density operation, particularly at low Pt loadings. State of the art electrodes are fabricated in an ink deposition process that leads to uncontrolled electrode architecture with random aggregates of functional domains (catalyst, ionomer, and pore volume) (1). The randomness in the domains induces high tortuosity transport pathways for ions and fluids, which cause severe transport resistance during high current density operation. Thin ionomer films cause additional transport resistance and poisoning of the Pt catalyst, which becomes more significant at low Pt loadings. Reducing the amount of ionomer in the catalyst domain without affecting the ionic transport resistance is key to improving the utilization of the Pt and reducing the transport resistance at low Pt loading. Rational design of the electrode structure with controlled low tortuous ionic transport pathways could improve performance. The introduction of the ionomer pathways could also enable reduction of the ionomer volume in the catalyst domain, reducing the transport resistance. Middelmen et al. proposed electrode structures consisting of aligned components in a low tortuosity configuration to improve performance (2). In this work, we present an alternative electrode structure based on a vertically aligned array of Nafion pillars in the cathode catalyst layer, as shown in Figure 1a. Figure 1b shows the SEM image of the Nafion pillars. Furthermore, Pt supported on carbon catalyst was deposited on the Nafion pillars to fabricate a meso-structured electrode. Nafion pillars provide high conductive and low tortuous pathways for protons, reducing the effective transport distance, and enabling reduction of the ionomer binder in the catalyst domain.

25 ENERGY STORAGE↗
DOE OSTI2021

Enhanced Performance of Pt Nanoparticles on Ni-N Co-Doped Graphitized Carbon for Oxygen Reduction Reaction in Polymer Electrolyte Membrane Fuel Cells

Since the reaction rate and cost for cathodic catalyst in polymer electrolyte membrane fuel cells are obstacles for commercialization, the high-performance catalyst for oxygen reduction reaction is necessary. The Ni encapsulated with N-doped graphitic carbon (Ni@NGC) prepared with ethylenediamine and carbon black is employed as an efficient support for the oxygen reduction reaction. Characterizations show that the Ni@NGC has a large surface area and mesoporous structure that is suitable to the support for the Pt catalyst. The catalyst structure is identified and the size of Pt nanoparticles distributed in the narrow range of 2–3 nm. Four different nitrogen species are doped properly into graphitic carbon structure. The Pt/Ni@NGC shows higher performance than the commercial Pt/C catalyst in an acidic electrolyte. The mass activity of the Pt/Ni@NGC in fuel cell tests exhibits over 1.5 times higher than that of commercial Pt/C catalyst. The Pt/Ni@NGC catalyst at low Pt loading exhibits 47% higher maximum power density than the Pt/C catalyst under H2-air atmosphere. These results indicate that the Ni@NGC as a support is significantly beneficial to improving activity.

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

Dynamics of polymer electrolyte with LiTFSI via Quasi-Elastic Neutron Scattering

Most lithium batteries offer a wide range of applications. However, safety issues are still an unresolved issue for several applications. To solve the safety issue of Li-ion batteries, solid polymer electrolyte is a promising candidate to replace commercial liquid electrolyte. A 4-arm star poly(ethylene oxide) polymer with LiTFSI salt as an electrolyte was studied. The dynamics of this polymer were explored with the Quasi-Elastic Neutron Scattering technique. Furthermore, the influence of temperature and Li salt concentration on the polymer dynamics was investigated. The dynamics of the polymer ends of the arm show much higher flexibility than the core parts making those types of polymers attractive for further studies in battery research.

Wang, Hui↗
DOE OSTI2020

Novel platinum group metal-free catalyst ink deposition system for combinatorial polymer electrolyte fuel cell performance evaluation

Here, a new system for rapid and precise fabrication of polymer electrolyte fuel cell (PEFC) membrane-electrode assemblies (MEAs) is introduced to facilitate rapid testing and characterization of platinum group metal-free (PGM-free) catalysts, with minimal waste of materials, using commercial combinatorial hardware and multi-channel potentiostat. The commercial combinatorial system, designed for high-throughput catalyst activity evaluation (i.e., low overpotential and current densities) using gas-diffusion electrodes (GDEs), has been further developed to enable simultaneous evaluation of the high current density performance on air of twenty-five cathodes prepared by coating catalyst-ionomer inks directly onto the membrane using a newly-developed deposition system. A nanopipette or micropipette coupled to a precise peristaltic pump is being used for precise and even catalyst ink deposition onto the membrane in each of twenty-five circular electrodes with areas of <1 cm 2 and in the precise locations required by the commercial combinatorial MEA hardware. The automated ink deposition system is coupled with a custom-designed heated vacuum table mounted on a computer-controlled XY stage to prevent deformation of the membrane and electrode layers during ink deposition onto the membrane. This system was utilized to evaluate the impact of ionomer to catalyst ratio on the hydrogen-air fuel cell performance of the PGM-free catalyst.

25 ENERGY STORAGE↗
DOE OSTI2023

Recent advancements in high performance polymer electrolyte fuel cell electrode fabrication – Novel materials and manufacturing processes

The global effort to introduce polymer electrolyte fuel cells for clean and renewable energy to the market is increasing the demand for high performance, robust and affordable membrane electrode assemblies (MEAs). There is not yet a standard method for large scale production of MEAs, or the methods employed are generally unsatisfactory in terms of quality and performance. A large number of published data of newly developed catalyst and electrolyte materials, claim to improve the state of the art, but are often not fully comparable due to different experimental studies and experimental designs. This article summarizes the trends in material developments and emerging MEA-manufacturing techniques. The materials and techniques are systematically compared in terms of cell performance and scalability. Current and future scientific challenges are identified and analysed based on published findings over the past five years. Finally, the results of the cited papers have been quantitatively compared to each other and to the internal benchmarks used in each cited work to provide a complete picture of the state of the art in PEFC MEA manufacturing.

25 ENERGY STORAGE↗
DOE OSTI2020

Interfacial engineering for stabilizing polymer electrolytes with 4V cathodes in lithium metal batteries at elevated temperature

Poly (ethylene oxide) (PEO) polymer electrolytes are promising candidates for next-generation rechargeable lithium batteries. However, the poor interfacial stability between 4 V cathodes and PEO electrolytes impedes their applications in 4 V lithium batteries with high energy density. Here, we demonstrate a facile and effective strategy to enhance the interfacial stability by the synergy of Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 (LAGP) coating on the cathode surface, and salt combination in the electrolyte, even with a cut-off voltage of 4.25–4.4 V vs. Li + /Li. Nano-LAGP coated Li|PEO|LiCoO 2 cell delivers stable cycling with a capacity retention of 81.9%/400 cycles and 84.7%/200 cycles at 60 °C when charged to 4.25 and 4.3 V in pure polyether electrolyte, respectively. Steady cycling is also demonstrated at room temperature and with LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523) cathode. This work offers a viable and scalable approach to improve the stability between PEO electrolytes and 4 V cathodes and open up new possibilities for practical application of 4 V lithium metal batteries.

25 ENERGY STORAGE↗
DOE OSTI2024

Multifunctional nitrile additives for inducing pseudo-concentration gel-polymer electrolyte: Enabling stable high-voltage lithium metal batteries

High-voltage lithium metal batteries (LMBs) are promising for next-generation high-energy storage systems. Unfortunately, their implementation has been severely plagued by the interfacial instability between the high-voltage cathodes/lithium metal (LM) anodes and electrolytes. To tackle these challenges, a novel nitrile additive, 1,4-dicyanobenzene (DCB) (Synonyms: terephthalonitrile), is added to the in situ polymerized pentaerythritol tetraacrylate-based gel polymer electrolyte (GPE). The DCB additive, as demonstrated both theoretically and experimentally, plays a crucial role in altering the Li+ coordinated solvation structure within the GPE. This alteration leads to the formation of a pseudo-concentrated electrolyte with a tightly packed Li+ cluster, expanding the electrochemical stability window of the electrolyte. Moreover, the DCB-included GPE significantly improves its compatibility with both LM anode and high-voltage cathode, attributed to the modified solvation structure and the generated LiF-rich electrolyte/electrode interphases. Accordingly, the GPE enables stable cyclic performance of LMBs based on a 4.9 V LiNi 0.5 Mn 1.5 O 4 cathode at a low relative negative/positive ratio of 4, achieving a high reversible capacity of 123.8 mAh g -1 with a capacity retention of 87.7% over 500 cycles at 0.5 C. This work provides new insights into enhancing the cyclability of high-voltage LMBs via the synergistic effect of additives and GPE.

25 ENERGY STORAGE↗
DOE OSTI2022

Parametric Study of the Influence of Support Type, Presence of Platinum on Support, and Ionomer Content on the Microstructure of Polymer Electrolyte Fuel Cell Catalyst Layers

We report Ultra-small angle X-ray scattering (USAXS) was employed to investigate the effects of carbon support type, the presence of platinum on carbon, and ionomer loading on the microstructure of polymer electrolyte fuel cell (PEFC) catalyst layers (CLs). Particle size distributions (PSDs), obtained from fitting the measured scattering data were used to interpret the size of carbon aggregates (40–300 nm) and agglomerates (>400 nm) from two-component carbon/ionomer and three-component platinum/carbon/ionomer CLs. Two types of carbon supports were investigated: high surface area carbon (HSC) and Vulcan XC-72. CLs with a range of perfluorosulfonic acid (PFSA) ionomer to carbon (I/C) ratios (0.2–1.2) and also with perfluoroimide acid (PFIA) ionomer were studied to evaluate the effect of ionomer on CL microstructure. The carbon type, the presence of platinum, and ionomer loading were all found to significantly impact carbon agglomeration. The extent of Pt/C agglomeration in the CL was found to increase with increasing ionomer and platinum concentration and to decrease with increasing carbon surface area. Platinum electrochemically-active surface area (ECSA) and local oxygen transport resistance (R nF ) were correlated to the CL microstructure to yield relationships affecting electrode performance.

25 ENERGY STORAGE↗
DOE OSTI2022

Integration of a high oxygen permeability ionomer into polymer electrolyte membrane fuel cell cathodes for high efficiency and power density

In this work, we present a study on the integration of a high oxygen permeability ionomer (HOPI) with high durability carbon supported platinum (Pt/C) catalysts to prepare cathode catalyst layers (CCLs) for polymer electrolyte membrane fuel cells (PEMFCs). A key motivation is the production of PEMFCs with high efficiency and durability for heavy-duty fuel cell vehicles. Our results from integrating a pre-commercial HOPI with robust, state-of-the-art catalysts with medium and low surface area carbon supports show significant increases in specific activities (67% increase over the standard commercial ionomer) at low current densities and reduced oxygen (O 2 ) transport resistances (R O2 ’s) at high current densities, enabling both higher efficiency and peak power density. The reduction in the R O2 with the HOPI is most significant at low relative humidity (RH), due to its more rigid backbone structure resisting compaction at lower water contents. In our ink optimization analysis, we show that the HOPI in this study achieves its peak performance with an ionomer to carbon ratio (I/C) of 0.6 and a moderately alcohol-rich ink solvent when fabricating catalyst layers by the decal method with an automatic wet film coater.

08 HYDROGEN↗
DOE OSTI2025

Solvent Dynamics in Gel Polymer Electrolytes for Lithium–Sulfur Batteries

Li−sulfur (Li−S) batteries are promising as the next-generation energy storage technology but face challenges due to sluggish sulfur redox reaction (SRR) kinetics and a sulfur shuttling effect. While many studies have explored polycaprolactone (PCL)-based gel polymer electrolytes (GPEs) to address these issues, the influence of solvent properties, including dielectric constant (ϵ) and donor and acceptor numbers (DN and AN), remain unexplored despite their critical impact on performance and full-scale implementation. This study systematically compares three distinct electrolytes, dimethoxyethane (DME), dimethyl sulfoxide (DMSO), and tetraethylene glycol dimethyl ether (TEGDME)-paired with PCL, to correlate the varied solvent properties and their effects on the physical properties of the GPE, in terms of Li + transport and solvation, and polysulfide’s confinement. Among them, the DME-based GPE, with an intermediate DN, exhibited the lowest crystallinity (2.31%), highest ionic conductivity (7.49 mS/cm), and high Li + transference number (0.77). As a result, it achieved a specific capacity of 795 mAh/g sulfur and an average Coulombic efficiency of 97.5% after 120 cycles at C/5, outperforming its competitors. Operando Raman and UV−vis spectroscopy confirmed that PCL effectively confines long-chain polysulfides within its network, mitigating the shuttle effect and facilitating reversible polysulfide conversion. These findings demonstrate that GPEs with moderate DN values and balanced ϵ significantly enhance stability, extend cycle life, and improve rate performance for Li−S batteries. This work provides valuable insights into the design of advanced electrolyte systems for practical energy storage applications.

25 ENERGY STORAGE↗
DOE OSTI2022

Phosphonated polymers, and methods of production thereof, for use as polymer electrolyte membranes (PEMs) and/or catalyst ionomeric binders for electrodes in PEM fuel cells

The present disclosure provides phosphonated polymers that can be used, for example, as polymer electrolyte membranes (PEMs) and/or catalyst ionomeric binders for electrodes in PEM fuel cells, and more particularly for high-temperature PEM fuel cells. High-temperature PEM fuel cells that use phosphonated polymers of the present disclosure suffer from reduced or no acid leaching because, in at least some examples, phosphonic acid moieties are covalently bound to the backbone of the polymers. A phosphonated polymer include a backbone having one or more aromatic monomers, with each aromatic monomer having one or more phosphonic acid groups. A phosphonic acid group may include phosphonic acid or a functional group that is hydrolysable into phosphonic acid.

Park, Eun Joo↗
DOE OSTI2021

Slot-die-coating operability windows for polymer electrolyte membrane fuel cell cathode catalyst layers

Roll-to-roll (R2R) slot-die coating of polymer electrolyte membrane fuel cell (PEMFC) catalyst layers represents a scalable deposition method for producing 10–20 m 2 ·min -1 of catalyst-coated gas diffusion layers (GDLs). This high-throughput production technique will help lower the cost of PEMFC catalyst layers. The uniformity of the wet layer applied by slot die deposition is affected by process parameters such as substrate speed, vacuum pressure applied at the upstream meniscus, gap between the slot die lips and substrate, ink rheology, and other ink and substrate properties. The set of conditions for producing a defect-free coating with a dilute ink typically requires little to no upstream vacuum pressure, so suitable operating conditions can be found easily through trial and error and operator intuition. However, the higher viscosity of more concentrated inks dramatically shifts the range of settings that result in a homogeneous coating to higher vacuum levels, which are harder to find through hit or miss. A predictive model showing the range of operable conditions decreases material wastage inherent in experimentally searching for suitable parameters. In this study, the defect-free coating parameter window is explored experimentally and theoretically for two concentrations of PEFC cathode inks. Both a full capillary hydrodynamic model and a computationally cheaper viscocapillary model successfully predict the experimentally determined coating window within the experimental and model uncertainty limits for inks with 5.3 wt% and 12.0 wt% solids ink while maintaining the 0.1 mg Pt ·cm -2 Pt areal loading target. Here, this paper demonstrates a viable pathway for meeting the $30/kW net ultimate cost target of the United States Department of Energy (U.S. DOE) Hydrogen Fuel Cells Technologies Office (HFTO). The concentrated ink lowers the thermal energy and capital expenditure (CapEx) budget of the coating process by decreasing the amount of time, energy, and floorspace required for drying the coating.

25 ENERGY STORAGE↗
DOE OSTI2022

Ionic Conductivity Enhancement of Polymer Electrolytes by Directed Crystallization

Here, we report that hot stretching of poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) can lead to a preferred orientation of PEO crystalline lamellae, thereby reducing the tortuosity of the ion-conduction pathway along the thickness direction of the SPE film, causing improved ionic conductivity. The hot stretching method is implemented by stretching SPE films above the melting point of PEO in an inert environment followed by crystallization at room temperature while maintaining the applied strain. The effect of hot stretching on the crystalline orientation, crystallinity, morphology, and ion transport in PEO with two types of salts, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium triflate (LiCF3SO3), is investigated in detail. Wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS) show that the orientation of PEO crystalline lamellae induces the formation of a short ion-conduction pathway along the through-plane direction of the SPE films, leading to 1.4- to 3.5-fold enhancement in the through-plane ionic conductivity.

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

Dispersing Agents Impact Performance of Protonated Phosphonic Acid High-Temperature Polymer Electrolyte Membrane Fuel Cells

The microstructure of ionomers plays a significant role in the performance of high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). Here, we establish direct correlations between the properties of dispersing agents and the microstructure of a protonated phosphonic acid ionomer. Most importantly, the formation of the porous structure of a protonated phosphonic acid ionomer depends on the pK a of the liquid media. Namely, the acid–base interaction between the charged polymer and dispersing agents determines the porosity in the ionomer thin films. The HT-PEMFC performance increases with the level of porosity of the ionomer, as the pores enable fast reactant gas accessibility. Overall, this study concludes the importance of the pK a of ionomers’ dispersing media for the HT-PEMFC performance.

25 ENERGY STORAGE↗
DOE OSTI2020

Energetics of Base–Acid Pairs for the Design of High-Temperature Fuel Cell Polymer Electrolytes

The interaction energy of base–acid plays a key role in acid retention of phosphoric acid (PA)-doped polymer electrolytes under fuel cell operating conditions. Here, we investigate the energetics of proton-accepting and hydroxide-donating organic bases using density functional theory calculations. Because of their weak basicity, proton-accepting organic bases such as benzimidazole have relatively low interaction energy with the acid in the absence of water (15.3–28.0 kcal mol –1 ). Energetics of the proton-accepting base–PA complex increases by adding water, indicating that the interactions in the base–acid complex strengthen in the presence of water. On the other hand, hydroxide-donating organic bases, such as tetramethylammonium hydroxide, have high interaction energy with PA (~110 kcal mol –1 ), which remains high in the presence of water. The chemical shifts of 31P NMR support the energetics of the base–acid complexes. Overall, this study further discusses the benefit of incorporating hydroxide-donating organic bases into the polymeric structure over proton-accepting bases as a way to increase acid retention.

25 ENERGY STORAGE↗
DOE OSTI2022

Coupled continuum and network model framework to study catalyst layers of polymer electrolyte fuel cells

The nanostructured thin film (NSTF) catalyst layers which have demonstrated high power densities, mass activities, and exceptional metal and support stability can have limited operational robustness due to their thin thickness and the hydrophilicity of the metal-coated nano whiskers. The dispersed nanostructured thin film (dNSTF) catalyst layers have been developed by dispersing the NSTF Pt whiskers with ionomer and carbon support to increase the thickness and hydrophobicity. Continuum and network models (NM) are coupled through boundary conditions to study the polymer electrolyte fuel cell with a dNSTF cathode catalyst layer. The coupled model combines the computational efficiency of the continuum model with the pore-scale information in the dNSTF cathode catalyst layer of the NM. It captures the special morphology of the partially ionomer/water covered cylindrical whiskers, as well as water percolation through the pore structures and their impact on the cell performance. Here we observe optimal ionomer coverage on whiskers to be 0.5, ionomer to carbon ratio to be 0.9 and higher whisker to carbon ratios to be desired.

08 HYDROGEN↗
DOE OSTI2023

Role of Intra-Domain Heterogeneity on Ion and Polymer Dynamics in Block Polymer Electrolytes: An Approach for Spatially Resolving Dynamics and Ion Transport

The design of safe and high-performance, nanostructured, block polymer (BP) electrolytes for lithium-ion batteries requires a thorough understanding of the key parameters that govern local structure and dynamics. Yet, the interfaces between microphase separated domains can introduce complexities in this local behavior that can be challenging to quantify. Herein, the local polymer, cation (Li + ), and anion dynamics were described in salt-doped polystyrene block poly(oligo-oxyethylene methyl ether methacrylate) (PS-b-POEM) through a quantitative framework that considered the effects of polymer architecture, segmental mixing, chain stretching, and confinement on polymer mobility and ion transport. This framework was validated through nuclear magnetic resonance (NMR) spectroscopy measurements on solid (dry) polymer electrolyte samples. Notably, a mobility transition temperature (T mobility ) was identified through NMR spectroscopy that captured the local dynamics more accurately than the thermal glass transition temperature. Additionally, the approach quantitatively described the mobility gradient across a domain when segmental mixing effects were combined with chain stretching and confinement information, especially at higher segregation strengths – facilitating the assessment of local ion diffusion and conductivity. As a result, spatially averaged local ion diffusion predictions quantitatively matched NMR-measured ion diffusivities in the BP samples, while spatially summed ionic conductivity predictions across a domain qualitatively captured trends in the measured ionic conductivities.

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

Polymer electrolytes based on protic ionic liquids with perfluorinated anions for safe lithium-ion batteries

Here, the quest for safe and high-performance polymer electrolytes in lithium-ion batteries (LIBs) has led researchers to explore protic ionic liquids (PILs) as potential candidates to be entrapped in polymer matrices. In this context, we present an investigation into solid polymeric systems based on poly(methyl methacrylate) (PMMA) as a host for PILs, featuring 1,8-diazabicyclo-[5,4,0]-undec-7-ene (DBU) cation paired with three different anions: bis(trifluoromethanesulfonyl)imide (TFSI – ), trifluoromethanesulfonate (TFO – ), and (trifluoromethanesulfonyl-nonafluorobutylsulfonyl)imide (IM14 – ). Additionally, we explore the lithium-doped IM14-gel-like system to broaden our understanding of these intriguing materials. Through comprehensive thermal analysis, solid-state NMR, and diffusion NMR techniques, we delve into the interactions and structural features of these binary and ternary polymeric systems. Our investigation reveals unique dynamics and ion interactions within the PMMA matrix, shedding light on the potential of these materials for advanced energy storage technologies. Particularly, we highlight the distinctive features of DBUH-IM14 and its specific interaction with the polymeric matrix and the lithium ions, underscoring its significance in advancing safer and more efficient energy storage devices.

25 ENERGY STORAGE↗