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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Neutron diffraction probing hydrogen in monoclinic H 2 VOPO 4

Light hydrogen atoms are resolvable with neutrons; however, the massive incoherent background inhibits the diffraction quality. To improve the signal, isotope treatment by deuteration becomes a prerequisite for a successful crystallographic understanding of hydrogen-containing materials by neutron diffraction. Thanks to the low-background and high-resolution time-of-flight neutron diffractometer, this work demonstrates a direct and successful measurement of high-quality neutron diffraction patterns of H 2 VOPO 4 powders, a precursor of a high-capacity alkali-ion battery cathode. The Rietveld refinement identifies the hydrogen coordinates, occupancy, and thermal parameters in the H 2 VOPO 4 lattice. Finally, the result highlights the unique capability of neutron diffraction for the structure characterization of hydrogen-containing materials, potentially without requiring costly and possibly artifact-inducing deuteration for neutron diffraction.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Thermodynamic and achievable efficiencies for solar-driven electrochemical reduction of carbon dioxide to transportation fuels

Thermodynamic, achievable, and realistic efficiency limits of solar-driven electrochemical conversion of water and carbon dioxide to fuels are investigated as functions of light-absorber composition and configuration, and catalyst composition. The maximum thermodynamic efficiency at 1-sun illumination for adiabatic electrochemical synthesis of various solar fuels is in the range of 32–42%. Single-, double-, and triple-junction light absorbers are found to be optimal for electrochemical load ranges of 0–0.9 V, 0.9–1.95 V, and 1.95–3.5 V, respectively. Achievable solar-to-fuel (STF) efficiencies are determined using ideal double- and triple-junction light absorbers and the electrochemical load curves for CO 2 reduction on silver and copper cathodes, and water oxidation kinetics over iridium oxide. The maximum achievable STF efficiencies for synthesis gas (H 2 and CO) and Hythane (H 2 and CH 4 ) are 18.4% and 20.3%, respectively. Whereas the realistic STF efficiency of photoelectrochemical cells (PECs) can be as low as 0.8%, tandem PECs and photovoltaic (PV)-electrolyzers can operate at 7.2% under identical operating conditions. Finally, we show that the composition and energy content of solar fuels can also be adjusted by tuning the band-gaps of triple-junction light absorbers and/or the ratio of catalyst-to-PV area, and that the synthesis of liquid products and C 2 H 4 have high profitability indices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

A high-energy-density lithium-oxygen battery based on a reversible four-electron conversion to lithium oxide

Lithium-oxygen (Li-O 2 ) batteries have attracted much attention owing to the high theoretical energy density afforded by the two-electron reduction of O 2 to lithium peroxide (Li 2 O 2 ). We report an inorganic-electrolyte Li-O 2 cell that cycles at an elevated temperature via highly reversible four-electron redox to form crystalline lithium oxide (Li 2 O). It relies on a bifunctional metal oxide host that catalyzes O–O bond cleavage on discharge, yielding a high capacity of 11 milliampere-hours per square centimeter, and O 2 evolution on charge with very low overpotential. Online mass spectrometry and chemical quantification confirm that oxidation of Li 2 O involves transfer of exactly 4 e – /O 2 . This work shows that Li-O 2 electrochemistry is not intrinsically limited once problems of electrolyte, superoxide, and cathode host are overcome and that coulombic efficiency close to 100% can be achieved.

Xia, C. (ORCID:0000000344062337)↗
DOE OSTI2015

Systems and methods for preparation and separation of products

There are provided methods and systems for an electrochemical cell including an anode and a cathode where the anode is contacted with a metal ion that converts the metal ion from a lower oxidation state to a higher oxidation state. The metal ion in the higher oxidation state is reacted with hydrogen gas, an unsaturated hydrocarbon, and/or a saturated hydrocarbon to form products.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2026

Electrochemically mediated disproportionation for selective formaldehyde upcycling in acid

Formaldehyde (FA) electrolysis is attractive for paired production of value‑added chemicals. However, conventional electrolysis adopts alkaline electrolytes, which triggers FA self-disproportionation and severe feed loss. Here we introduce a sustainable and selective strategy for valorizing FA through electrochemically mediated disproportionation in acidic electrolytes. By leveraging a dual-electrode system consisting of a hydrophobic copper tetraminophthalocyanine layer (CuTAPc-layer) cathode and a Pt 2 Ru bimetallic anode, we efficiently convert FA into methanol and formic acid at high Faradaic efficiencies of 93.2% and 91.3%, respectively. Compared with alkaline FA oxidation, which can lose up to 76% FA and complicate downstream separation, the acidic system suppresses side reactions to ensure high product purity. Mechanism studies reveal that the hydrophobic microenvironment of CuTAPc-layer suppresses hydrogen evolution, while the stronger oxophilicity of Pt 2 Ru enhances FA activation and lowers the key deprotonation barrier for FA oxidation. The integrated device demonstrates application potential in polyoxymethylene upgrading, delivering 374.2 mA at 4 V with ~90% single-pass conversion, establishing a scalable and eco-friendly electrochemical pathway for chemical upcycling.

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

Charting the relationship between phase type-surface area-interactions between the constituent atoms and oxygen reduction activity of Pd–Cu nanocatalysts inside fuel cells by in operando high-energy X-ray diffraction

The activity and stability of nanoalloy catalysts for chemical reactions driving devices for clean energy conversion, in particular the oxygen reduction reaction (ORR), depend critically on optimizing major structural characteristics of the nanoalloys, such as the phase composition, surface area and bonding interactions between the constituent atoms, for the harsh operating conditions inside the devices. The effort requires good knowledge of the potential effect of changes in these characteristics on the catalytic functionality of the nanoalloys and, hence, on the devices' performance. We present the results from an in operando high-energy X-ray diffraction (HE-XRD) study on the concurrent changes in the structural characteristics and ORR activity of Pd–Cu nanoalloy catalysts as they function at the cathode of a proton exchange membrane fuel cell (PEMFC). We find that the as-prepared Pd–Cu nanoalloys with a chemical composition close to Pd1Cu1 are better ORR catalysts in comparison with Pd1Cu2, i.e. Pd-poor, and Pd3Cu1, i.e. Pd-rich, nanoalloys. Under operating conditions though, the former suffers a big loss in ORR activity appearing as a slow-mode oscillation in the current output of the PEMFC. Losses in ORR activity suffered by the latter also exhibit sudden drops and rises during the PEMFC operation. Through atomic pair distribution function (PDF) analysis of the in operando HE-XRD data, we identify the structural changes of Pd–Cu alloy NPs that are behind the peculiar decay of their ORR activity. The results uncover the instant link between the ever-adapting structural state of ORR nanocatalysts inside an operating PEMFC and the performance of the PEMFC. Besides, our results indicate that, among others, taking control over the intra-particle diffusion of metallic species in nanoalloy catalysts may improve the performance of PEMFCs significantly and, furthermore, in operando HE-XRD can be an effective tool to guide the effort. Finally, we argue that, though showing less optimal ORR activity in the as-prepared state, monophase Pd–Cu alloy catalysts with a composition ranging between Pd1Cu1 and Pd3Cu1 may deliver optimal performance inside operating PEMFCs.

Maswadeh, Yazan↗
DOE OSTI2023

Hierarchically Porous Carbons with Highly Curved Surfaces for Hosting Single Metal FeN 4 Sites as Outstanding Oxygen Reduction Catalysts

Iron–nitrogen–carbon (Fe₋N₋C) materials have emerged as a promising alternative to platinum-group metals for catalyzing the oxygen reduction reaction (ORR) in proton-exchange-membrane fuel cells. However, their low intrinsic activity and stability are major impediments. Herein, an Fe₋N–C electrocatalyst with dense FeN 4 sites on hierarchically porous carbons with highly curved surfaces (denoted as FeN 4 - hc C) is reported. The FeN 4 - hc C catalyst displays exceptional ORR activity in acidic media, with a high half-wave potential of 0.85 V (versus reversible hydrogen electrode) in 0.5 m H 2 SO 4 . When integrated into a membrane electrode assembly, the corresponding cathode displays a high maximum peak power density of 0.592 W cm -2 and demonstrates operating durability over 30 000 cycles under harsh H 2 /air conditions, outperforming previously reported Fe–N₋C electrocatalysts. These experimental and theoretical studies suggest that the curved carbon support fine-tunes the local coordination environment, lowers the energies of the Fe d-band centers, and inhibits the adsorption of oxygenated species, which can enhance the ORR activity and stability. This work provides new insight into the carbon nanostructure–activity correlation for ORR catalysis. It also offers a new approach to designing advanced single-metal-site catalysts for energy-conversion applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Methods and systems for fuel production in electrochemical cells and reactors

Methods and systems for fuel, chemical, and/or electricity production from electrochemical cells are disclosed. A voltage is applied between an anode and a cathode of an electrochemical cell. The anode includes a metal or metal oxide electrocatalyst. Oxygen is supplied to the cathode, producing oxygen ions. The anode electrocatalyst is at least partially oxidized by the oxygen ions transported through an electrolyte from the cathode to the anode. A feed gas stream is supplied to the anode electrocatalyst, which is converted to a liquid fuel. The anode electrocatalyst is re-oxidized to higher valency oxides, or a mixture of oxide phases, by supplying the oxygen ions to the anode. The re-oxidation by the ions is controlled or regulated by the amount of voltage applied.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2020

In-situ and in-operando analysis of voltage losses using sense wires for proton exchange membrane water electrolyzers

Proton exchange membrane water electrolyzer development requires understanding processes at the materials and interface levels to reach the required performance and lifetime targets for increasing market penetration. To achieve the required progress, it is critical to develop advanced in-situ diagnostics that allow observation of the changes that come with the reduction of catalyst loading combined with long-term intermittent operation. This work presents an internal voltage sensing method that enables observing internal voltage drops in an operating electrolyzer cell. It allows the total cell resistance to be separated into anode, CCM, and cathode resistance. The method is demonstrated by operating cells with different anode porous transport layers (PTLs). The changing properties of the PTLs result in significant variations of the resistances. Enhancing the PTL properties with a protective coating reduces the anode resistance significantly. In addition to these observations, the method enables a real-time monitoring of resistance related values that impact performance in water electrolyzers. Long-term experiments with the method allow us to gain insights into processes that occur during operation such as conditioning or degradation. The internal voltage sensing method presented in this study is a novel technique for diagnosing, analyzing, and optimizing water electrolyzers and other energy conversion devices.

42 ENGINEERING↗
DOE OSTI2017

Rational fabrication of nickel hydroxide shell on TiO{sub 2} nanorod core forming enhanced arrays for energy storage

Highlights: • Construct TiO{sub 2}/Ni(OH){sub 2} core/shell arrays by ALD-assisted HS method. • Ni(OH){sub 2} nanoflake shells show high energy storage. • Porous core/shell structure is favorable for fast ion/electron transfer. - Abstract: Integration of different functional materials into core/shell composite arrays is of great importance for high-performance energy storage. In this work, we controllably synthesize Ni(OH){sub 2} nanoflake shell on the single-crystalline TiO{sub 2} nanorod cores forming composite core/shell arrays (CSAs). Interconnected Ni(OH){sub 2} nanoflakes of 20–30 nm are uniformly coated on the TiO{sub 2} nanorods of 80–120 nm via atomic layer deposition assisted hydrothermal method. Furthermore, porous network with numerous nanopores and large surface area is formed in this core/shell structure. In view of this advantageous architecture, the designed Ni(OH){sub 2}/TiO{sub 2} CSAs are studied as cathode of alkaline batteries and show high energy storage performance with a capacity of 121 mAh g{sup −1} at 1 A g{sup −1} and 91 mAh g{sup −1} at 5 A g{sup −1}, respectively. The boosted electrochemical properties are owing to the porous core/shell architecture with improved active area and accelerated ion/electron transfer characteristics.

36 MATERIALS SCIENCE↗
DOE OSTI2021

All-in-one bipolar electrode: A new concept for compact and efficient water electrolyzers

Highly compact and efficient proton exchange membrane electrolyzer cells (PEMECs) are strongly desired for commercializing hydrogen production. Here, a novel concept of all-in-one bipolar electrode (AIOBE) is proposed for high-efficiency and compact PEMECs with the help of 3D printing and sputtering coating. AIOBE ideally integrated catalyst layer (CL)/gas diffusion layer/bipolar plate/current distributor/gasket, which significantly reduced component quantity on the cathode side of PEMECs from 5 to 1, cut down on part weight and volume, and drastically accelerated the fabrication and maintenance processes. Moreover, AIOBE with the micro-scale flat surface and nano-scale rough CL provided an ultralow ohmic resistance (~100 mOhm cm 2 ) and a high catalyst utilization. Finally, AIOBE delivered a practical voltage of 1.62 V and a high energy efficiency of 91% at 1000 mA/cm 2 , and its mass activity (4.48 A/mg Pt ) was 14 times higher than conventional PEMECs. In conclusion, this work provides a new route for developing highly compact electrochemical devices, such as fuel cells, electrolyzers for N 2 reduction and CO 2 conversion, and many more.

3D printing↗
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 OSTI2026

Understanding Inlet Concentration Effects on the Electrocatalytic Conversion of CO 2 to Formic Acid in Gas-Fed Electrolyzers

The electrochemical CO 2 reduction reaction (CO2RR) to produce value-added products remains a developing technology for utilizing waste CO 2 streams. Most device-level CO2RR studies use pure CO 2 gas feeds; however, the effect of dilute CO 2 on the electrolyzer performance is an important consideration for large-scale electrolyzer operation, single-pass conversion, and real-world CO 2 source utilization. This work investigates the effect that the CO 2 concentration has on the performance of formic acid (HCOOH) producing tin oxide (SnO 2 ) and bismuth oxide (Bi 2 O 3 ) catalysts in an electrolyzer device setting. Surprisingly, SnO2 demonstrated an approximately 20% increase in HCOOH selectivity (Faradaic efficiency) when the CO 2 concentration decreased from 100 to 20%. In contrast, Bi 2 O 3 consistently demonstrated high selectivity toward HCOOH across the same CO 2 concentration range. The effects of the CO 2 concentration on selectivity were further investigated with half-cell experiments and in situ Raman spectroscopy, which revealed dynamic changes in the cathodic overpotential and chemical state of the catalyst that depended on the CO 2 concentration. Density functional theory calculations showed how changes in the surface oxidation state of Sn, varying from fully oxidized SnO 2 to metallic Sn(0), affect the thermodynamic barriers of the three main observed products: HCOOH, CO, and H 2 . Our results indicate that dilute CO 2 concentrations required larger cathodic overpotentials to sustain a fixed current density, which, in turn, pushed the Sn-based catalyst toward a more reduced surface that was favorable to HCOOH formation. On the other hand, the Bi-based catalyst remained in a metallic state at CO2RR-relevant potentials and demonstrated a consistent product selectivity regardless of CO 2 concentration. These findings highlight how varying the CO 2 inlet gas concentrations affects the chemical state of catalysts and the resulting performance metrics.

42 ENGINEERING↗
DOE OSTI2020

Electrocatalytic Valorization into H2 and Hydrocarbons of an Aqueous Stream Derived from Hydrothermal Liquefaction

Electrocatalytic oxidation is an attractive process for valorizing the carbon and removal of nitrogen present in the aqueous waste streams at ambient conditions. Here, we evaluated the electrocatalytic oxidation as a function of applied potential over a commercial Pt electrode of aqueous waste stream generated via hydrothermal liquefaction. We validated the conversion of quantifiable carbon (e.g., carboxylic acids, alpha hydroxyacids, alcohols, ketones, amides) and unquantifiable carbon as well as nitrogen removal. The unquantifiable carbon was valorized to quantifiable short chain organic molecules (e.g., acetic). Model studies showed that carboxylic acids, alcohol and ketones converted following (non-) Kolbe chemistry. Amides and alpha hydroxyacids formed carboxylic acids that subsequently converted via (non-) Kolbe chemistry. Ammonia was oxidized into N2. The reaction rate varied for each molecule family with carboxylic acids and ammonia having the highest reaction rates. The main reaction products from the electrocatalytic oxidation at the anode were volatile, short chain hydrocarbons (i.e., olefins, paraffins) and CO generated via Kolbe chemistry, while H2 was generated at the cathode. The parallel denitrification, valorization of carbon, and H2 generation of the aqueous waste can replace and simplify the current unit operations used in a commercial hydrothermal liquefaction process. The high operation potential required to drive the electrocatalytic reaction is responsible for high operation costs; however, they can be either partially subsidized with sale of excess H2 at the current DOE goal of $2/kg H2. Thus, the present work shows how electrocatalytic oxidation can be used to valorize aqueous waste streams into volatile hydrocarbons and H2.

Electrocatalytic oxidation, Aqueous waste valoriza↗
DOE OSTI2025

Solvent-Free Melt-Processed Cathode Mitigates Li Anode Instability in Polymer-Based Solid-State Batteries

Solvent-free manufacturing of battery components is a promising alternative to traditional slurry processing for reducing the cost and environmental impact. In this work, we used twin-screw melt extrusion to fabricate a polymer-based high voltage composite cathode. The melt-processed cathode is dense (near zero porosity) and thick (65 μm) and has high active material loading (80 wt %). The active particles are distributed uniformly throughout the melt-processed cathode, unlike the traditional slurry-cast cathode, which exhibits inhomogeneous particle distribution. In the melt-processed cathode, polymer and carbon form separate phases, whereas in the slurry-cast cathode they blend into a single phase. Due to these structural differences, the melt-processed cathode shows smooth charge–discharge profiles, while the slurry-cast cathode shows noisy charging and soft-shorting behavior. In conclusion, this work highlights that twin-screw extrusion as a scalable, solvent-free manufacturing method is advantageous in producing uniform cathodes, which mitigates anode instability.

25 ENERGY STORAGE↗
DOE OSTI2024

Electrochemical Conversion of CO 2 to Methyl Formate in a Flow Electrolyzer with Mixed Propylene Carbonate/Methanol Catholyte

Despite the promise of electrochemical carbon dioxide reduction as a technology for the production of clean fuels and decarbonization of the chemical industry, research has mostly focused on aqueous systems with a relatively limited set of products that have been achieved via electrosynthesis. Increasingly, CO 2 electroreduction in nonaqueous solvents is being pursued to develop new avenues for expanding the suite of products that can be made with high selectivity. CO 2 reduction in alcohols coupled with in situ esterification to produce esters is one such route that utilizes nonaqueous electrolyte. To be practical, such electrochemical syntheses need to be translated to a high-performance reactor such as a flow electrolyzer. However, many organic solvents, such as alcohols, wet and flood porous electrodes, thus impeding reactor performance. In this work, methanol was mixed with propylene carbonate as a catholyte for a gas-fed CO 2 flow electrolyzer that avoided cathode flooding. Simultaneously, a dual aqueous anolyte was used for water oxidation as a scalable and sustainable anodic half-reaction. The performance effect of methanol concentration, catholyte acidity, CO 2 flow rate, and dilute water in the catholyte were investigated. With 10 vol % methanol in 90 vol % propylene carbonate, 63% faradaic efficiency for methyl formate ester product was sustained without cathode flooding. However, improvements are still needed to lower the cell resistance and further increase the operating current density.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

High-Potential Electrocatalytic O2 Reduction with Nitroxyl / NOx Mediators: Implications for Fuel Cells and Aerobic Oxidation Catalysis

Efficient reduction of O2 to water is a central challenge in energy conversion and aerobic oxidation catalysis. In the present study, we investigate the electrochemical reduction of O2 with soluble organic nitroxyl and nitrogen oxide (NOx) mediators. When used alone, neither organic nitroxyls, such as TEMPO (2,2,6,6-tetramethyl-1-piperidinyl-N-oxyl), nor NOx species, such as sodium nitrite, are effective mediators of electrochemical O2 reduction. The combination of nitroxyl/NOx species, however, mediates sustained O2 reduction at electrochemical potentials of 0.19–0.33 V (vs. Fc/Fc+) in acetonitrile containing trifluoroacetic acid. Mechanistic analysis of the coupled redox reactions supports a process in which the nitrogen oxide catalyst drives aerobic oxidation of a nitroxyl mediator to an oxoammonium species, which then is reduced back to the nitroxyl at the cathode. The electrolysis potential is dictated by the oxoammonium/nitroxyl reduction potential. The high potentials observed with this ORR system benefit from the mechanism-based specificity for four-electron reduction of oxygen to water mediated by NOx species, together with kinetically efficient reduction of oxidized NOx species by TEMPO and other organic nitroxyls. This research was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center, funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.

Gerken, James B.↗