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All sources NASA NTRS DOE OSTI

DOE OSTI2022

More Powerful Twistron Carbon Nanotube Yarn Mechanical Energy Harvesters

We report that stretching a coiled carbon nanotube (CNT) yarn can provide large, reversible electrochemical capacitance changes, which convert mechanical energy to electricity. Here, it is shown that the performance of these “twistron” harvesters can be increased by optimizing the alignment of precursor CNT forests, plastically stretching the precursor twisted yarn, applying much higher tensile loads during precoiling twist than for coiling, using electrothermal pulse annealing under tension, and incorporating reduced graphene oxide nanoplates. The peak output power for a 1 and a 30 Hz sinusoidal deformation are 0.73 and 3.19 kW kg -1 , respectively, which are 24- and 13-fold that of previous twistron harvesters at these respective frequencies. This performance at 30 Hz is over 12-fold that of other prior-art mechanical energy harvesters for frequencies between 0.1 and 600 Hz. The maximum energy conversion efficiency is 7.2-fold that for previous twistrons. Twistron anode and cathode yarn arrays are stretched 180° out-of-phase by locating them in the negative and positive compressibility directions of hinged wine-rack frames, thereby doubling the output voltage and reducing the input mechanical energy.

36 MATERIALS SCIENCE↗

NASA NTRS1984

Electrodynamic Tethers. 1: Power Generator in LEO. 2: Thrust for Propulsion and Power Storage

An electrodynamic tether consists of a long insulated wire in space whose orbital motion cuts across lines of magnetic flux to produce an induce voltage that in typical low orbits averages about 200 v/km. Such a system should be capable of generating substantial electrical power, at the expense of IXB drag acting on its orbital energy. If a reverse current is driven against the induced voltage, the system should act as a motor producing IXB thrust. A reference system was designed, capable of generating 20 KW of power into an electrical load located anywhere along the wire at the expense of 2.6N (20,000 J/sec) drag on the wire. In an ideal system, the conversion between mechanical and electrical energy would reach 100% efficiency. In the actual system part of the 20 KW is lost to internal resistance of the wire, plasma and ionosphere, while the drag force is increased by residual air drag. The 20 KW PMG system as designed is estimated to provide 18.7 KW net power to the load at total drag loss of 20.4 KJ/sec, or an overall efficiency of 92%. Similar systems using heavier wire appear capable of producing power levels in excess of 1 Megawatt at voltages of 2-4 KV, with conversion efficiency between mechanical and electrical power better than 95%. The hollow cathode based system should be readily reversible from generator to motor operation by driving a reverse current using onboard power.

Mccoy, J. E.↗

DOE OSTI2014

High-Current Cold Cathode Employing Diamond and Related Materials

The essence of this project was for diamond films to be deposited on cold cathodes to improve their emission properties. Films with varying morphology, composition, and size of the crystals were deposited and the emission properties of the cathodes that utilize such films were studied. The prototype cathodes fabricated by the methods developed during Phase I were tested and evaluated in an actual high-power RF device during Phase II. These high-power tests used the novel active RF pulse compression system and the X-band magnicon test facility at US Naval Research Laboratory. In earlier tests, plasma switches were employed, while tests under this project utilized electron-beam switching. The intense electron beams required in the switches were supplied from cold cathodes embodying diamond films with varying morphology, including uncoated molybdenum cathodes in the preliminary tests. Tests with uncoated molybdenum cathodes produced compressed X-band RF pulses with a peak power of 91 MW, and a maximum power gain of 16.5:1. Tests were also carried out with switches employing diamond coated cathodes. The pulse compressor was based on use of switches employing electron beam triggering to effect mode conversion. In experimental tests, the compressor produced 165 MW in a ~ 20 ns pulse at ~18× power gain and ~ 140 MW at ~ 16× power gain in a 16 ns pulse with a ~ 7 ns flat-top. In these tests, molybdenum blade cathodes with thin diamond coatings demonstrated good reproducible emission uniformity with a 100 kV, 100 ns high voltage pulse. The new compressor does not have the limitations of earlier types of active pulse compressors and can operate at significantly higher electric fields without breakdown.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Coordination Polymer Electrocatalysts Enable Efficient CO‐to‐Acetate Conversion

Abstract Upgrading carbon dioxide/monoxide to multi‐carbon C 2+ products using renewable electricity offers one route to more sustainable fuel and chemical production. One of the most appealing products is acetate, the profitable electrosynthesis of which demands a catalyst with higher efficiency. Here, a coordination polymer (CP) catalyst is reported that consists of Cu(I) and benzimidazole units linked via Cu(I)‐imidazole coordination bonds, which enables selective reduction of CO to acetate with a 61% Faradaic efficiency at −0.59 volts versus the reversible hydrogen electrode at a current density of 400 mA cm −2 in flow cells. The catalyst is integrated in a cation exchange membrane‐based membrane electrode assembly that enables stable acetate electrosynthesis for 190 h, while achieving direct collection of concentrated acetate (3.3 molar) from the cathodic liquid stream, an average single‐pass utilization of 50% toward CO‐to‐acetate conversion, and an average acetate full‐cell energy efficiency of 15% at a current density of 250 mA cm −2 .

Luo, Mingchuan↗

DOE OSTI2024

Enhancing Direct Electrochemical CO 2 Electrolysis by Introducing A-Site Deficiency for the Dual-Phase Pr(Ca)Fe(Ni)O 3-δ Cathode

High-temperature CO 2 electrolysis via solid oxide electrolysis cells (CO 2 –SOECs) has drawn special attention due to the high energy convention efficiency, fast electrode kinetics, and great potential in carbon cycling. However, the development of cathode materials with high catalytic activity and chemical stability for pure CO 2 electrolysis is still a great challenge. In this work, A-site cation deficient dual-phase material, namely (Pr 0.4 Ca 0.6 ) x Fe 0.8 Ni 0.2 O 3-δ (PCFN, x = 1, 0.95, and 0.9), has been designed as the fuel electrode for a pure CO 2 –SOEC, which presents superior electrochemical performance. Among all these compositions, (Pr 0.4 Ca 0.6 ) 0.95 Fe 0.8 Ni 0.2 O 3-δ (PCFN95) exhibited the lowest polarization resistance of 0.458 Ω cm 2 at open-circuit voltage and 800 °C. The application of PCFN95 as the cathode in a single cell yields an impressive electrolysis current density of 1.76 A cm -2 at 1.5 V and 800 °C, which is 76% higher than that of single cells with stoichiometric Pr 0.4 Ca 0.6 Fe 0.8 Ni 0.2 O 3-δ (PCFN100) cathode. The effects of A-site deficiency on materials' phase structure and physicochemical properties are also systematically investigated. Such an enhancement in electrochemical performance is attributed to the promotion of effective CO 2 adsorption, as well as the improved electrode kinetics resulting from the A-site deficiency.

30 DIRECT ENERGY CONVERSION↗

DOE OSTI2014

2013 Estorm - Invited Paper - Cathode Materials Review

The electrochemical potential of cathode materials defines the positive side of the terminal voltage of a battery. Traditionally, cathode materials are the energy-limiting or voltage-limiting electrode. One of the first electrochemical batteries, the voltaic pile invented by Alessandro Volta in 1800 (Phil. Trans. Roy. Soc. 90, 403 431) had a copper-zinc galvanic element with a terminal voltage of 0.76 V. Since then, the research community has increased capacity and voltage for primary (nonrechargeable) batteries and round-trip efficiency for secondary (rechargeable) batteries. Successful secondary batteries have been the lead acid with a lead oxide cathode and a terminal voltage of 2.1 V and later the NiCd with a nickel(III) oxide hydroxide cathode and a 1.2 V terminal voltage. The relatively low voltage of those aqueous systems and the low round-trip efficiency due to activation energies in the conversion reactions limited their use. In 1976, Wittingham (J. Electrochem. Soc., 123, 315) and Besenhard (J Power Sources 1(3), 267) finally enabled highly reversible redox reactions by intercalation of lithium ions instead of by chemical conversion. In 1980, Goodenough and Mizushima (Mater. Res. Bull. 15, 783 789) demonstrated a high-energy and high-power LiCoO2 cathode, allowing for an increase of terminal voltage far beyond 3 V. Over the past four decades, the international research community has further developed cathode materials of many varieties. Current state-of-the-art cathodes demonstrate voltages beyond any known electrolyte stability window, bringing electrolyte research once again to the forefront of battery research.

Daniel, Claus↗

DOE OSTI2019

Redox Catalytic and Quasi-Solid Sulfur Conversion for High Capacity Lean Lithium Sulfur Batteries

The practical deployment of lithium sulfur batteries demands stable cycling of high loading and dense sulfur cathodes under lean electrolyte conditions, which is very difficult to realize. We describe here a strategy of fabricating extremely dense sulfur cathodes, designed by integrating Mo6S8 nanoparticles as a multi-functional mediator with a Li-ion conducting binder and a high-performance Fe3O4@N-carbon sulfur host. The Mo6S8 nanoparticles have substantially faster Li-ion insertion kinetics compared with sulfur, and the produced LixMo6S8 particles have spontaneous redox reactivity with relevant polysulfide species (such as Li4Mo6S8 + Li2S4 <-> Li3Mo6S8 + Li2S, Delta G = -84 kJ mol(-1)), which deliver a true redox catalytic sulfur conversion mechanism. In addition, LixMo6S8 particles strongly absorb polysulfide during battery cycling, which provides a quasi-solid sulfur conversion pathway and almost eliminated polysulfide dissolution. Such a pathway not only promotes growth of uniform Li2S that can be readily charged back with nearly no overpotential, but also mitigates the polysulfide-induced Li metal corrosion issue. The combination of these benefits enables stable and high capacity cycling of dense sulfur cathodes under a low electrolyte to sulfur ratio (4.2 mu L mg(-1)), as demonstrated with cathodes with volumetric capacities of at least 1.3 Ah cm(-3) and capacity retentions of similar to 80% for 300 cycles. Furthermore, stable cycling of batteries under a practically relevant N/P ratio of 2.4 is also demonstrated.

lean electrolyte↗

DOE OSTI2024

Spatial Progression of Polysulfide Reactivity with Lithium Nitrate in Li–Sulfur Batteries

LiNO 3 is a commonly used electrolyte additive in Li-S batteries, but the intricacies of its stabilizing effect on these batteries are not well-understood due to the complex chemical nature of Li-S electrolytes. This complexity often hampers clear characterization and interpretation of data. In this study, we explore the reactivity of LiNO 3 in Li-S batteries through in operando sulfur K-edge spectroscopy. To remove ambiguities, a sulfur-free electrolyte with LiNO 3 as the sole salt is used. This allows a precise elucidation of the reaction mechanism between LiNO 3 and polysulfides. Here, we observe that the reaction is chemical in nature and progresses spatially, influenced by the polysulfide concentration gradient across the electrolyte. Polysulfides are electrochemically generated in situ on the cathode side, leading to high local concentration. As a result, they cannot be fully oxidized by LiNO 3 and forms sulfites initially which are gradually further oxidized into sulfonates and sulfates. Conversely, polysulfides on the anode side have lower local concentration as they are not generated in situ but diffused from the cathode side. Their reaction with LiNO 3 leads to highly oxidized species like sulfonates and sulfates. These reaction products are not reduced during electrochemically cycling, suggesting their capabilities of passivating the electrodes and contributing to the cycle stabilities of Li-S batteries.

25 ENERGY STORAGE↗

NASA NTRS1991

Thermion: Verification of a thermionic heat pipe in microgravity

The Idaho National Engineering Laboratory (INEL) is conducting intensive research in the design and development of a small excore heat-pipe-thermionic space nuclear reactor power system (SEHPTR). The SEHPTR spacecraft will be able to supply 40 kW of power in any given orbit. The key components in this reactor are the thermionic heat pipes. The heat pipes have two major functions: (1) to convert heat energy into electrical energy, and (2) to radiate the excess heat to space. Thermionic power conversion is the process of converting heat energy into electrical energy with no moving parts. Heat is applied to the cathode surface. This heat will boil off electrons that will jump across the gap to the cooler surface of the anode, which will cause a potential difference between the two plates and induce a current through the load. Thermionic power conversion is incorporated as part of the heat pipe. The heat pipe, which is being developed by Thermacore Inc., is actually two heat pipes. It uses a radial heat pipe, called the emitter, and an axial heat pipe collector. The emitter heat pipe will pass the heat from the nuclear core to the cathode surface. The collector heat pipe keeps the anode surface cooler by transferring the heat from the anode surface and radiating it to space.

Source record↗

DOE OSTI2022

Decoupling mass transport and electron transfer by a double-cathode structure of a Li-O 2 battery with high cyclic stability

Aprotic lithium-oxygen (Li-O 2 ) batteries have attracted extensive attention due to their ultrahigh theoretical energy density. However, slow and undesired electron transfer during cathodic reactions causes low cyclic stability in these batteries. Here, in this paper, we demonstrate that O 2 mass transport and electron transfer for cathodic reactions in Li-O 2 batteries could be decoupled by a double-cathode structure that efficiently enables stable electron transfer between the cathode and Li 2 O 2 /O 2 . This resolves various side reactions and slow Li 2 O 2 reaction kinetics issues in conventional Li-O 2 batteries, leading to stable operation of the cell for nearly 2 months at a capacity of 0.2 and 5 mAh cm -2 , with more than 4- and 10-fold increases in cycle life when compared with single-cathode batteries. These remarkable improvements in the cyclic stability of Li-O 2 batteries with double cathodes provide an interesting concept for improving the operational stability of other metal-rechargeable batteries with conversion-type chemistry.

25 ENERGY STORAGE↗

DOE OSTI2018

Improving the Electrocatalytic Activity and Durability of the La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ Cathode by Surface Modification

Electrode materials with high activity and good stability are essential for commercialization of energy conversion systems such as solid oxide fuel cells or electrolysis cells at the intermediate temperature. Modifying the existing perovskite-based electrode surface to form a heterostructure has been widely applied for the rational design of novel electrodes with high performance. Despite many successful developments in enhancing electrode performance by surface modification, some controversial results are also reported in the literature and the mechanisms are still not well understood. In this work, the mechanism of how surface modification impacts the oxygen reduction reaction (ORR) activity and stability of perovskite-based oxides was investigated. We took La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 (LSCF) as the thin-film model system and modified its surface with additive Pr x Ce 1–x O 2 layers of different thicknesses. We found a strong correlation between surface oxygen defects and the ORR activity of the heterostructure. By inducing higher oxygen vacancy concentration compared to bare LSCF, PrO 2 coating is proved to greatly facilitate the rate of oxygen dissociation, thus significantly enhancing the ORR activity. Because of low oxygen vacancy density introduced by Pr 0.2 Ce 0.8 O 2 and CeO 2 coating, on the one hand, it does not boost the rate of ORR but successfully suppresses surface Sr segregation, leading to an enhanced durability. Our findings will demonstrate the vital role of surface oxygen defects and provide important insights for the rational design of high-performance electrode materials through surface defect engineering.

25 ENERGY STORAGE↗

DOE OSTI2023

Stabilization of a co-bound intermediate via molecular tuning promotes CO2-to-ethylene conversion

Aspects included herein include an electrolytic system for electrochemical reduction of carbon dioxide, the system comprising: a cathode comprising: a porous gas-diffusion membrane permeable to CO 2 ; an electrocatalyst layer adjacent to a second side of the gas-diffusion membrane; the electrocatalyst layer comprising: an electrically conductive catalyst; and a selectivity-determining organic material attached to at least a portion of the electrically conductive catalyst; wherein: the organic material is formed of a plurality of oligomers; each oligomer comprises a plurality of covalently bonded base units; each base unit comprises at least one heterocyclic group having at least one nitrogen in its structure; and an anion exchange membrane adjacent to the electrocatalyst layer and positioned between the anode and the cathode; wherein anion exchange membrane is characterized by anion conductivity and the cathode is in ionic communication with the anode via the anion exchange membrane.

Agapie, Theodor↗

DOE OSTI2023

Ni Anchored to Hydrogen-Substituted Graphdiyne for Lithium Sulfide Cathodes in Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries are promising candidates for next-generation energy storage systems due to their high theoretical energy density and the low cost of sulfur. However, slow conversion kinetics between the insulating S and lithium sulfide (Li 2 S) remains as a technical challenge. In this work, we report a catalyst featuring nickel (Ni) single atoms and clusters anchored to a porous hydrogen-substituted graphdiyne support (termed Ni@HGDY), which is incorporated in Li 2 S cathodes. The rapidly synthesized catalyst was found to enhance ionic and electronic conductivity, decrease the reaction overpotential, and promote more complete conversion between Li 2 S and sulfur. The addition of Ni@HGDY to commercial Li 2 S powder enabled a capacity of over 516 mAh g Li 2 S –1 at 1 C for over 125 cycles, whereas the control Li 2 S cathode managed to maintain just over 200 mAh g Li 2 S –1 . In conclusion, these findings highlight the efficacy of Ni as a metal catalyst and demonstrate the promise of HGDY in energy storage devices.

25 ENERGY STORAGE↗

DOE OSTI2015

Electrochemically influenced cation inter-diffusion and Co 3 O 4 formation on La 0.6 Sr 0.4 CoO 3 infiltrated into SOFC cathodes

Nanosized LSC electrocatalyst was infiltrated into a porous scaffold cathode composed of Sm 2 O 3 -doped CeO 2 (SDC) and La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) in a commercial button solid oxide fuel cell (SOFC). To understand the stability of cathodes infiltrated with LSC, the infiltrated composite cells were subjected to both electrochemical operating and thermal aging states at 750 °C for 1500 h. Nanostructure and local chemistry evolution of La 0.6 Sr 0.4 CoO 3 (LSC) infiltrated cathodes upon operation and aging were investigated by transmission electron microscopy. After operation, the LSC remained a cubic perovskite, and the crystal grains exhibit comparable size to as-infiltrated LSC grains. Inter-diffusion of Fe from the LSCF to a Fe-incorporated LSC layer developed on the LSCF backbone. However, only sharp interfaces were observed between LSC and SDC backbone in the as-infiltrated cathode and such interfaces remain after operation. The infiltrated LSC on the SDC backbone also retains granular particle morphology. Furthermore, newly grown Co 3 O 4 nanocrystals were found in the operated cathode. After thermal aging, on the other hand, cation inter-diffusion across the interfaces of the infiltrate particles and the cathode backbones is less than that from the operated cells. Lastly, the following hypothesis is proposed: Co 3 O 4 forms on LSC arising from local charge balancing between cobalt and oxygen vacancies.

30 DIRECT ENERGY CONVERSION↗

DOE OSTI2019

Core-Shell Heterostructures as Solid Oxide Fuel Cell Electrodes Quarterly Report

The goals of the project are to synthesize and deploy core-shell heterostructures as solid oxide fuel cell (SOFC) cathodes which exhibit high oxygen reduction rates at lower operating temperatures resulting in high performance at lower operating temperature and simultaneously exhibit longterm resistance to Cr-impurity attack induced performance degradation. An ancillary objective is to eliminate cumbersome, multiple infiltration steps in the cathode to achieve high performance. The expected outcomes are (1) a novel, environmentally benign, and inexpensive synthesis tool for synthesizing complex cathode powders, scalable to high volumes; (2) decrease in energy expenditure during synthesis of cathode powders; (3) up to a factor of 1.5 improvement in maximum power density of single cells at 700ºC; and (4) significant improvements in cell performance degradation rates down to 0.02%/1000 h.

20 FOSSIL-FUELED POWER PLANTS↗

DOE OSTI2014

Cathode materials review

The electrochemical potential of cathode materials defines the positive side of the terminal voltage of a battery. Traditionally, cathode materials are the energy-limiting or voltage-limiting electrode. One of the first electrochemical batteries, the voltaic pile invented by Alessandro Volta in 1800 (Phil. Trans. Roy. Soc. 90, 403-431) had a copper-zinc galvanic element with a terminal voltage of 0.76 V. Since then, the research community has increased capacity and voltage for primary (nonrechargeable) batteries and round-trip efficiency for secondary (rechargeable) batteries. Successful secondary batteries have been the lead-acid with a lead oxide cathode and a terminal voltage of 2.1 V and later the NiCd with a nickel(III) oxide-hydroxide cathode and a 1.2 V terminal voltage. The relatively low voltage of those aqueous systems and the low round-trip efficiency due to activation energies in the conversion reactions limited their use. In 1976, Wittingham (J. Electrochem. Soc., 123, 315) and Besenhard (J. Power Sources 1(3), 267) finally enabled highly reversible redox reactions by intercalation of lithium ions instead of by chemical conversion. In 1980, Goodenough and Mizushima (Mater. Res. Bull. 15, 783-789) demonstrated a high-energy and high-power LiCoO{sub 2} cathode, allowing for an increase of terminal voltage far beyond 3 V. Over the past four decades, the international research community has further developed cathode materials of many varieties. Current state-of-the-art cathodes demonstrate voltages beyond any known electrolyte stability window, bringing electrolyte research once again to the forefront of battery research.

25 ENERGY STORAGE↗

DOE OSTI2016

A Rechargeable Al/S Battery with an Ionic‐Liquid Electrolyte

Abstract Aluminum metal is a promising anode material for next generation rechargeable batteries owing to its abundance, potentially dendrite‐free deposition, and high capacity. The rechargeable aluminum/sulfur (Al/S) battery is of great interest owing to its high energy density (1340 Wh kg −1 ) and low cost. However, Al/S chemistry suffers poor reversibility owing to the difficulty of oxidizing AlS x . Herein, we demonstrate the first reversible Al/S battery in ionic‐liquid electrolyte with an activated carbon cloth/sulfur composite cathode. Electrochemical, spectroscopic, and microscopic results suggest that sulfur undergoes a solid‐state conversion reaction in the electrolyte. Kinetics analysis identifies that the slow solid‐state sulfur conversion reaction causes large voltage hysteresis and limits the energy efficiency of the system.

Gao, Tao↗

DOE OSTI2016

A Rechargeable Al/S Battery with an Ionic‐Liquid Electrolyte

Gao, Tao↗