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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 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

A Comprehensive Understanding of the Aging Effects of Extreme Fast Charging on High Ni NMC Cathode

As the battery industry shifts toward high Ni content cathodes, such as LiNi 0.8 Mn 0.1 Co 0.1 O 2 [NMC811], a complete understanding of the degradation mechanisms of NMC811 under extreme fast charging (XFC) (XFC, ≤10–15 min charging) conditions is needed. Such comprehensive understanding would identify the most critical materials gaps that need to be addressed for enabling XFC long-life cells for electric vehicles. This study maps out the key aging mechanisms for NMC811 cycled at different XFC conditions (between 1C and 9C) for up to 1000 cycles. To acquire a fundamental understanding of utilization and degradation, cells are evaluated using a range of electrochemical techniques, and multimodal and multiscale microscopy techniques to quantify chemical, structural, and crystallographic degradation as a function of cycling conditions for the NMC cathode. When comparing NMC811 to NMC532, it is observed that NMC811 has a greater subsurface crystallographic degradation and displays a similar magnitude of subparticle cracking. However, the NMC811 maintains superior performance despite those advanced degradations. Here, the superior cycle life performance is attributed to the NMC811 particles having radially oriented grains and improved transport properties. NMC811 shows between 4.6× and 3.15× reduction in capacity fade than NMC532 for charging rates between 4C (e.g., 15-min charging) and 6C (10-min charging).

25 ENERGY STORAGE↗
DOE OSTI2023

Alternative Energy Carriers: Unique Interfaces for Electrochemical Hydrogenic Transformations

Abstract The shift toward renewable energy generation sources, characterized by their non‐carbon emitting but variable nature, has spurred significant innovation in energy storage technologies. Advancements in foundational understanding from investments in basic science and clever engineering solutions, coupled with increasing industrial adoption, have resulted in a notable reduction in the cost of storing electricity from variable energy generation sources. These developments have paved the way for the exploration of new and innovative forms of energy storage that deviate from traditional technologies. In this perspective, it is posited that the progress made in energy storage research over recent years has opened the door to the development of energy carriers for technologies that are yet to be realized. To illustrate this concept, examples of alternative energy carriers are provided within the context of unique electrochemical interfaces for electrochemical hydrogenic transformations. The unique properties of these interfaces and electrochemical systems can be leveraged in ways not yet imagined, creating new possibilities for energy storage. A perspective on the progress and challenges for each interface as well as a general outlook for the advancement of energy carrier systems are provided.

25 ENERGY STORAGE↗
DOE OSTI2023

Conjugated Imine Polymer Synthesized via Step‐Growth Metathesis for Highly Stable Silicon Nanoparticle Anodes in Lithium‐Ion Batteries

Abstract This work reports a new method to synthesize polyphenylmethanimine (polyPMI) as a linear or a hyperbranched, conjugated polymer using an aldehyde‐imine metathesis reaction. This work details the reaction mechanisms of this polymerization by characterizing a red‐shift in its absorption spectrum as polymer conjugation length increases and verifies that this optical shift results from extended π‐condensation using density functional theory. This new synthetic approach provides a polymer that can potentially be depolymerized for facile recyclability and is compatible with air‐ and water‐sensitive chemistries. As an example of the utility of this new approach, this work demonstrates that this polymer can be directly grown on silicon nanoparticles to create silicon anodes for lithium‐ion batteries with a high degree of electrochemical interfacial passivation. These silicon anodes exhibit Coulombic efficiencies above 99.9% and can accommodate silicon nanoparticle expansion and contraction during lithiation and delithiation as demonstrated by stable reversible capacities for 500 cycles. Finally, this work demonstrates that polyPMI facilitates the formation of a lithium fluoride rich solid electrolyte interphase that remains chemically and mechanically stable after long term cycling.

25 ENERGY STORAGE↗
DOE OSTI2025

An Active Oxygen Electrode for Proton-Conducting Solid Oxide Electrolysis Cells with High Faradaic Efficiency

Addressing the challenges posed by inferior electrochemical performance at low temperatures and the uncertain Faradaic efficiency (FE) represents a pivotal undertaking in the development of high performance and efficient proton-conducting solid oxide electrolysis cells (P-SOECs). In this work, a novel oxygen electrode material BaCo0.8Zr0.1Zn0.1O3-d (BCZZ) is first designed and synthesized. At 600 °C, P-SOECs with BCZZ oxygen electrode achieve an electrolysis current density of 1.98 A cm-2 with an ˜90% FE at 1.3 V. Utilizing 1-inch P-SOECs as a reliable platform, the effect of extrinsic operating conditions (i.e., steam concentration, voltage, current density, and temperature) and intrinsic properties of P-SOECs (i.e., electrolyte material and electrolyte thickness) on FE are further systemically investigated, both experimentally and theoretically.

08 - HYDROGEN↗
DOE OSTI2026

Engineering Thermally Resilient and Kinetically Active Reversible Protonic Ceramic Cells via Interfacial Design

Achieving concurrent fast electrode kinetics and long-term thermo-mechanical durability remains a critical challenge for reversible protonic ceramic electrochemical cells (R-PCECs). Herein, we report an interfacial engineering strategy that integrates a perovs.kite-type PrBaRu0.1Co1.9O5+δ (PBRC) nanoparticle layer onto a PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF) substrate (PBRC-PBSCF), together with a modified pellet-assisted sintering approach to fabricate dense BaZr0.4Ce0.4Y0.1Yb0.1O3-δ (BZCYYb4411) electrolytes. The in situ reconstructed heterointerface enhances oxygen reduction/evolution reaction (ORR/OER) kinetics, promotes H2O adsorption/dissociation, and improves steam tolerance, as verified by electrochemical measurements and interfacial microstructural analyses. Density functional theory reveals that Ru-induced electronic modulation at the PBRC-PBSCF interface lowers the energy of oxygen vacancy formation and optimizes the position of the O 2p band center, thereby accelerating oxygen redox kinetics and stabilizing the interface. The resulting R-PCECs deliver an excellent peak power density of 1.112 W cm−2 and an electrolysis current density of −1.257 A cm−2 at 1.3 V in 3% H2O wet air at 600°C, with a reasonable faradaic efficiency. Furthermore, the cells demonstrate excellent stability, sustaining 100 h of thermal cycling (400–600°C, 200°C h−1) in both fuel cell and electrolysis modes, with 600 h of stability in electrolysis mode (600°C, −0.5 to −2 A cm−2).

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2015

Potassium-induced effect on structure and chemical activity of Cu x O/Cu(111) (x≤2) surface: A combined scanning tunneling microscopy and density functional theory study

Potassium (K) plays an essential role in promoting catalytic reaction in many established industrial catalytic processes. Here, we report a combined study using scanning tunneling microscopy (STM) and density functional theory (DFT) in understanding the effect of depositing K on the atomic and electronic structures as well as chemical activities of Cu x O/Cu(111) (x≤2). The DFT calculations observe a pseudomorphic growth of K on Cu x O/Cu(111) up to 0.19 monolayer (ML) of coverage, where K binds the surface via strong ionic interaction with chemisorbed oxygen and the relatively weak electrostatic interactions with copper ions, lower and upper oxygen on the Cu x O rings. The simulated STM pattern based on the DFT results agrees well with the experimental observations. The deposited K displays great impact on the surface electronic structure of Cu x O/Cu(111), which induces significant reduction in work function and leads to a strong electron polarization on the surface. The promotion of K on the surface binding properties is selective. It varies depending on the nature of adsorbates. According to our results, K has little effect on surface acidity, while it enhances the surface basicity significantly. As a consequence, the presence of K does not help for CO adsorption on Cu x O/Cu(111), but being able to accelerate the activation of CO 2 . Thus, such promotion strongly depends on the combinations from both geometric and electronic effects. Our results highlight the origin of promoting effect of alkalis in the design of catalysts for the complex reactions.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2024

Modeling Planar Electrodes and Zero–Gap Membrane Electrode Assemblies for CO 2 Electrolysis

Multiphysics modeling enables probing of conditions inside a CO 2 electrolyzer that are difficult to measure, such as local concentrations and pH, as well as rapid testing of possible design changes. A one-dimensional model for a zero-gap membrane electrode assembly (MEA) CO 2 electrolyzer was developed with the assumption that catalyst layers interact with the membrane ionomer such that the ionomer affects the underlying kinetics. The kinetics for bicarbonate reacting to form hydrogen are fit using a planar electrode model for silver with an ionomer coating. The MEA model results are validated against experimental studies for current density and product selectivity. Flooding of the cathode is modeled using saturation curves, and results show that blocked pores in the microporous layer play a significant role in limiting the mass transport at high potentials (>2.8 V). Sensitivity studies showed that CO Faradaic efficiency can be increased by decreasing catalyst layer thickness and porosity, and decreasing KHCO 3 concentration.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2024

Theoretical Investigation of the Adsorbate and Potential–Induced Stability of Cu Facets During Electrochemical CO 2 and CO Reduction

The activity and product selectivity of electrocatalysts for reactions like the carbon dioxide reduction reaction (CO 2 RR) are intimately dependent on the catalyst's structure and composition. While engineering catalytic surfaces can improve performance, discovering the key sets of rational design principles remains challenging due to limitations in modeling catalyst stability under operating conditions. Herein, we perform first-principles density functional calculations adopting implicit solvation methods with potential control to study the influence of adsorbates and applied potential on the stability of different facets of model Cu electrocatalysts. Using coverage dependencies extracted from microkinetic models, we describe an approach for calculating potential and adsorbate-dependent contributions to surface energies under reaction conditions, where Wulff constructions are used to understand the morphological evolution of Cu electrocatalysts under CO 2 RR conditions. Here we identify that CO*, a key reaction intermediate, exhibits higher kinetically and thermodynamically accessible coverages on (100) relative to (111) facets, which can translate into an increased relative stabilization of the (100) facet during CO 2 RR. Our results support the known tendency for increased (111) faceting of Cu nanoparticles under more reducing conditions and that the relative increase in (100) faceting observed under CO 2 RR conditions is likely attributed to differences in CO* coverage between these facets.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2019

Understanding the Oxygen Reduction Reaction Activity and Oxidative Stability of Pt Supported on Nb-Doped TiO 2

Commercial fuel cell electrocatalyst degradation results from carbon electrocatalyst support oxidation at high operating potential transients. Guided by density functional theory (DFT) calculations, Nb-doped TiO 2 (NTO) was synthesized, which exhibits a unique combination of high surface area, high electrical conductivity, and high porosity. Here, this catalyst retained 78 % of its initial electrochemically active surface area compared with 57.6 % retained by Pt/C following the DOE/FCCJ protocol for accelerated stability test. Strong metal–support interactions, which were predicted by DFT calculations and confirmed experimentally by X-ray photoelectron spectroscopy and kinetics measurements, resulted in 21 % higher oxygen reduction reaction mass activity (at 0.9 V vs. reversible hydrogen electrode) on Pt/NTO compared with commercial Pt/C. The ex situ activity and durability of Pt/NTO translated to a fuel cell. The rise in electrode ohmic resistance and non-electrode concentration overpotential indicate that improving the conductivity of NTO and optimizing the catalyst ink formulation are critical next steps in the development of Pt/NTO-catalyzed proton exchange membrane fuel cells.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2023

Parasitic Effects in Impedance Spectrum of PEM Water Electrolysis Cells: Case Study of High-Frequency Inductive Effects

Electrochemical impedance spectroscopy (EIS) is a powerful tool to characterize and distinguish electrochemical, electrical, and diffusive processes in an electrolysis cell. The EIS response with small impedance (mΩ) depends on components and materials of the cell, but often also on the electrical setup, cables, and connectors, leading to incorrect conclusions about the performance of the electrolysis cells. These parasitic effects are assessed via a short-circuit measurement and confirmed to be external from the membrane electrode assembly (MEA). In the setup, the inductive characteristic is described by a modified inductive reactance and must be included in the equivalent circuit model (ECM) which is fitting the cell EIS spectra in operation (in situ). If points of the spectra showing inductive characteristic (below x-axis in Nyquist plot) are excluded from the ECM evaluation, an artificially increased ohmic resistance at high frequencies is obtained. In addition, considerations on other components of the ECM can be misleading and significantly incorrect. The only way to avoid that inductive behavior caused by the external setup is incorrectly assigned to the ECM describing properties of the MEA is to include the inductive effects in the ECM analysis of in situ EIS measurements.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2016

Understanding Water Transport in Polymer Electrolyte Fuel Cells Using Coupled Continuum and Pore-Network Models

Water management remains a critical issue for polymer electrolyte fuel cell performance and durability, especially at lower temperatures and with ultrathin electrodes. To understand and explain experimental observations better, water transport in gas diffusion layers (GDLs) with macroscopically heterogeneous morphologies was simulated using a novel coupling of continuum and pore-network models. X-ray computed tomography was used to extract GDL material parameters for use in the pore-network model. The simulations were conducted to explain experimental observations associated with stacking of anode GDLs, where stacking of the anode GDLs increased the limiting current density. Through imaging, it is shown that the stacked anode GDL exhibited an interfacial region of high porosity. The coupled model shows that this morphology allowed more efficient water movement through the anode and higher temperatures at the cathode compared to the single GDL case. As a result, the cathode exhibited less flooding and hence better low temperature performance with the stacked anode GDL.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2017

Utilizing a Segmented Fuel Cell to Study the Effects of Electrode Coating Irregularities on PEM Fuel Cell Initial Performance

An understanding of the impact of coating irregularities on beginning of life polymer electrolyte fuel cell (PEMFC) performance is essential to develop and establish manufacturing tolerances for its components. Coating irregularities occurring in the fuel cell electrode can either possess acceptable process variations or potentially harmful defects. A segmented fuel cell (SFC) is employed to understand how 100% catalyst reduction irregularities ranging from 0.125 to 1 cm 2 in the cathode electrode of a 50 cm 2 sized cell impact spatial and total cell performance at dry and wet humidification conditions. Here, by analyzing the data in a differential format the local performance effects of irregularity sizes down to 0.25 cm 2 were detected in the current distribution of the cell. Slight total cell performance impacts, due to irregularity sizes of 0.5 and 1 cm 2 , were observed under dry operation and high current densities.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2020

The Effect of Membrane Casting Irregularities on Initial Fuel Cell Performance

Membrane electrode assemblies (MEA) for polymer electrolyte membrane fuel cells (PEMFC) may possess as-manufactured non-uniformities in any of its constituent components. This article studies casting irregularities located within the PEM to understand their potential impact on MEA initial performance. Membrane material was cast on a lab-scale polymer casting line operating either within or at the boundaries of the process window. The resulting membrane material was either pristine in the former case, or, in the latter case, contained air bubbles, cracks, and other irregularities, ranging in size from about 0.6 to 3 mm. Spatial polarization experiments were conducted using a 121-channel segmented fuel cell system, and thermal imaging was performed subsequently to map hydrogen crossover to spatial performance. While total-cell polarization data was minimally impacted by the irregularities, the spatial diagnostics showed local performance impacts that, in operation over time, could cause degradation in performance or earlier failure of the MEA. Such impacts could lead to these irregularities being classified as defects, i.e., manufacturing variations that should be identified and not included in a fuel cell stack. Classification of irregularities as defects will ultimately assist the industry by contributing to the development of threshold detection limits for in-line quality control diagnostics.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2023

Crack detection in fuel cell electrodes using a spatial filtering technique for overcoming noisy backgrounds

Image processing is a powerful tool that allows for rapid and automated data parsing in settings that occupy large variable spaces and require large data sets. Feature detection on difficultly discerned backgrounds is a subset of image processing that facilitates the extraction of quantitative metrics from otherwise subjective data. Crack detection and quantification is an important capability in polymer electrolyte membrane fuel cell quality control, failure analysis, and optimization. This work presents a technique to perform crack detection and quantification which overcomes challenges faced by commonly used image segmentation techniques. We demonstrate the use of a geometrically filtered noise‐level detection technique to select a binary threshold value from which we then quantify how cracked a sample is. Furthermore, we demonstrate the accuracy of our technique using programmatically generated test images of known crack amounts and their performance on real‐world fuel cell catalyst layer samples.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2015

Impact of hygrothermal aging on structure/function relationship of perfluorosulfonic-acid membrane

Perfluorosulfonic-acid (PFSA) membranes are widely used as the solid electrolyte in electrochemical devices where their main functionalities are ion (proton) conduction and gas separation in a thermomechanically stable matrix. Due to prolonged operational requirements in these devices, PFSA membranes’ properties change with time due to hygrothermal aging. This paper studies the evolution of PFSA structure/property relationship changes during hygrothermal aging, including chemical changes leading to changes in ion-exchange capacity (IEC), nanostructure, water-uptake behavior, conductivity, and mechanical properties. Our findings demonstrate that with hygrothermal aging, the storage modulus increases, while IEC and water content decrease, consistent with the changes in nanostructure, that is, water- and crystalline-domain spacings inferred from small- and wide-angle X-ray scattering (SAXS/WAXS) experiments. In addition, the impact of aging is found to depend on the membrane's thermal prehistory and post-treatments, although universal correlations exist between nanostructural changes and water uptake. Lastly, the findings have impact on understanding lifetime, durability, and use of these and related polymers in various technologies.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2021

Binary and Ternary Colloidal Cu–Sn–Te Nanocrystals for Thermoelectric Thin Films

Recent advances in copper chalcogenide-based nanocrystals (NCs), copper sulfide, and copper selenide derived nanostructures, have drawn considerable attention. However, reports of crystal phase and shape engineering of binary or ternary copper telluride NCs remain rare. Here, a colloidal hot-injection approach for producing binary copper/tin telluride, and ternary copper tin telluride NCs with controllable compositions, crystal structures, and morphologies is reported. Here, the crystal phase and growth behavior of these tellurides are systematically studied from both experimental and theoretical perspectives.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2023

Dynamic In‐Plane Heterogeneous and Inverted Response of Graphite to Fast Charging and Discharging Conditions in Lithium‐Ion Pouch Cells

Solutions for improving fast charging of lithium‐ion batteries have largely focused on alleviating through‐plane lithiation gradients while little is understood about in‐plane heterogeneities and how to resolve them. Herein, high‐speed synchrotron X‐ray diffraction (XRD) resolves graphite lithiation spatially and temporally during 6 C charging and 2 C discharging. At every point during operation, considerable differences in the state of lithiation across the pouch cell are present. Some regions are more responsive to operation than others, reaching full lithiation early during charge and full delithiation during discharge. Other regions within the cell never fully delithiate during discharge, despite a prolonged voltage hold at 2.8 V. Using time‐resolved XRD data, the calculated local current density (mA cm −2 ) at the graphite surface shows an unexpected occurrence of local inverted current densities where regions of graphite are observed to delithiate during charging and lithiate during discharging. A pseudo‐3D model is developed for the graphite electrode with spatially varying microstructural tortuosity to show how microstructural heterogeneity could influence spatial charge dynamics. The model could not predict the complex in‐plane charge behavior observed within the cell. Consequently physics‐based charging protocols based on homogeneous electrode assumptions may underestimate the local variations in charge dynamics and occurrence of lithium plating.

25 ENERGY STORAGE↗