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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

Microbial sensor system for the assessment of subsurface environments

A microbial sensor, system, and method that can be used to determine a chemical environment and/or substrate concentrations in anaerobic or aerobic environments, such as soils, sediments and ground waters, are disclosed. An exemplary system uses one or more (e.g., inert) measurement electrodes and a reference electrode. The reference electrode can include an electrode exposed to atmospheric oxygen (e.g., a cathode) or an electrode exposed to stable anaerobic or aerobic conditions. The exemplary microbial sensor system measures open-circuit voltage to characterize the chemical (oxidizing or reducing) environment and/or recovery voltage to measure substrate concentrations in the subsurface.

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

Microbial sensor system for the assessment of subsurface environments

A microbial sensor, system, and method that can be used to determine a chemical environment and/or substrate concentrations in anaerobic or aerobic environments, such as soils, sediments and ground waters, are disclosed. An exemplary system uses one or more (e.g., inert) measurement electrodes and a reference electrode. The reference electrode can include an electrode exposed to atmospheric oxygen (e.g., a cathode) or an electrode exposed to stable anaerobic or aerobic conditions. The exemplary microbial sensor system measures open-circuit voltage to characterize the chemical (oxidizing or reducing) environment and/or recovery voltage to measure substrate concentrations in the subsurface.

Burge, Scott R.↗
DOE OSTI2022

An Unbalanced Battle in Excellence: Revealing Effect of Ni/Co Occupancy on Water Splitting and Oxygen Reduction Reactions in Triple–Conducting Oxides for Protonic Ceramic Electrochemical Cells

Porous electrodes that conduct electrons, protons, and oxygen ions with dramatically expanded catalytic active sites can replace conventional electrodes with sluggish kinetics in protonic ceramic electrochemical cells. In this work, a strategy is utilized to promote triple conduction by facilitating proton conduction in praseodymium cobaltite perovskite through engineering non-equivalent B-site Ni/Co occupancy. Surface infrared spectroscopy is used to study the dehydration behavior, which proves the existence of protons in the perovskite lattice. The proton mobility and proton stability are investigated by hydrogen/deuterium (H/D) isotope exchange and temperature-programmed desorption. It is observed that the increased nickel replacement on the B-site has a positive impact on proton defect stability, catalytic activity, and electrochemical performance. This doping strategy is demonstrated to be a promising pathway to increase catalytic activity toward the oxygen reduction and water splitting reactions. The chosen PrNi 0.7 Co 0.3 O 3–δ oxygen electrode demonstrates excellent full-cell performance with high electrolysis current density of –1.48 A cm –2 at 1.3 V and a peak fuel-cell power density of 0.95 W cm –2 at 600 °C and also enables lower-temperature operations down to 350 °C, and superior long-term durability.

08 HYDROGEN↗
DOE OSTI2022

A Perspective on ferroelectricity in hafnium oxide: Mechanisms and considerations regarding its stability and performance

Ferroelectric hafnium oxides are poised to impact a wide range of microelectronic applications owing to their superior thickness scaling of ferroelectric stability and compatibility with mainstream semiconductors and fabrication processes. For broad-scale impact, long-term performance and reliability of devices using hafnia will require knowledge of the phases present and how they vary with time and use. In this Perspective article, the importance of phases present on device performance is discussed, including the extent to which specific classes of devices can tolerate phase impurities. Following, the factors and mechanisms that are known to influence phase stability, including substituents, crystallite size, oxygen point defects, electrode chemistry, biaxial stress, and electrode capping layers, are highlighted. Herein, discussions will focus on the importance of considering both neutral and charged oxygen vacancies as stabilizing agents, the limited biaxial strain imparted to a hafnia layer by adjacent electrodes, and the strong correlation of biaxial stress with resulting polarization response. Areas needing additional research, such as the necessity for a more quantitative means to distinguish the metastable tetragonal and orthorhombic phases, quantification of oxygen vacancies, and calculation of band structures, including defect energy levels for pure hafnia and stabilized with substituents, are emphasized.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Dynamic stability of active sites in hydr(oxy)oxides for the oxygen evolution reaction

The poor activity and stability of electrode materials for the oxygen evolution reaction are the main bottlenecks in the water-splitting reaction for H 2 production. In this work, by studying the activity–stability trends for the oxygen evolution reaction on conductive M 1 O x H y , Fe–M 1 O x H y and Fe–M 1 M 2 O x H y hydr(oxy)oxide clusters (M 1 = Ni, Co, Fe; M 2 = Mn, Co, Cu), we show that balancing the rates of Fe dissolution and redeposition over a MO x H y host establishes dynamically stable Fe active sites. Together with tuning the Fe content of the electrolyte, the strong interaction of Fe with the MO x H y host is the key to controlling the average number of Fe active sites present at the solid/liquid interface. We suggest that the Fe–M adsorption energy can therefore serve as a reaction descriptor that unifies oxygen evolution reaction catalysis on 3 d transition-metal hydr(oxy)oxides in alkaline media. Thus, the introduction of dynamically stable active sites extends the design rules for creating active and stable interfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2022

The Role of Oxygen in Lithiation and Solid Electrolyte Interphase Formation Processes in Silicon-Based Anodes

Silicon oxides (SiO x ) have been considered as promising alternatives to pure Si in high energy anodes in lithium-ion batteries (LIBs) due to their improved cycling stability. However, their fundamental lithiation mechanism has not yet been systematically investigated, and potential collateral downsides remain unclear. In this work, we report on the role of oxygen in lithiation/delithiation and solid electrolyte interphase (SEI) formation processes in SiO x thin film model electrodes with different oxygen contents. Here, we show that the SiO x anodes with higher oxygen content experience smaller volume change and form a thinner and more stable SEI, both of which are beneficial for cycling stability. However, these SiO x anodes also show an irreversible lithiation at around 0.7 V attributed to the reduction of Si oxides, leading to lower first cycle coulombic efficiency that is undesirable for practical applications. Overall, these results offer a balanced perspective on the advantages and disadvantages that oxygen brings to Si-based anodes in LIBs.

25 ENERGY STORAGE↗
DOE OSTI2022

On-Demand Designing of Cathode Internal Surface Architecture for Dramatic Enhancement of SOFC Performance and Durability

This project is aimed to design and modify the internal surfaces of porous composite cathode from currently commercially viable Solid Oxide Fuel Cells (SOFCs), using additive manufacturing process of Atomic Layer Deposition (ALD). The material systems being investigated are commercial composite electrodes complex three-dimensional topographies. In term of the chemistry of the ALD layer applied on the internal surface of the porous cathode, this project has employed commercially relevant electrolyte, electrocatalyst and noble metal materials set. Such materials are fully compatible with the commercial fuel cells, and this project has developed special nanostructure on the surface of the commercial composite cathodes. The formation of the designed nanoarchitecture on the surface of SOFC cathode has been achieved through precise control of ALD parameters and their effect on overall cell performance and resultant electrochemical reaction mechanism of cathodes has been investigated through full cell electrochemical performance testing and nanostructure characterization by transmission electron microscopy (TEM). Under the support of this award, following has been achieved: (1). For cathode materials in solid oxide fuel cells (SOFCs), such as perovskite mixed conductor La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-x (LSCF), cation surface segregation and consequently losing conductivity and active sites for the oxygen reduction reaction (ORR) are problematic. To mitigate the cation segregation and enhance SOFC durability, further decorating the internal backbone surface using the desired electrocatalysts could be a promoting approach. Commonly, the cation segregation such as Sr is very volatile, so the effective surface decoration is ideally conformal. Nevertheless, the conformal surface coating would inevitably alter the ORR pathways that initially take place on the surface of the backbone. To reveal the impact of the conformal coating on both the catalytic activity and the conductivity of the cathode, the unary electrocatalyst of Pt or CoO x , was applied to the LSCF/SDC composite electrode of inherently functional SOFCs, respectively. Both ALD coating layers evolve strong interaction with the LSCF composite cathode. Upon operations, the Pt coating layer remains conformal on LSCF grain surfaces but turns into discrete particles on SDC grain surfaces. Meanwhile, CoO x conformal coating grows to be the discrete nanograins on both the LSCF and SDC grains. ALD coating of the cathode alone reduces the ohmic resistance up to 28 % for the entire cells. The increased conductivity induced by the ALD coating of Pt or CoO x is ascribed to different mechanisms. For the inherent functional SOFCs, the present study presents a novel and feasible approach to apply a conformal, dense coating layer on the surface of a mixed conductor, simultaneously increasing the conductivity and durability of the SOFC cathode. (2). High resistance of the oxygen electrode still significantly hinders the state-of-the-art Solid Oxide Fuel Cells (SOFCs). In particular, for an oxygen electrode consisting of mixed electronic and ionic conductors, such as perovskite lanthanum strontium cobalt ferrite (LSCF), it deteriorates due to its low chemical stability of the grain surface. Such degradation is often associated with the segregation of cations. To prevent the cation surface segregation and its resultant perovskite phase decomposition, we demonstrate a conformal ultra-thin (7-10 nm) surface heterogeneous coating layer consisting of subjacent discrete Pt nanoparticles capped with a superjacent fully dense conformal CoO x layer. The performance studies indicate the ALD coating reduces the cell series resistance by up to 40 %. The conformal CoO x layer consists of randomly orientated but single-layered nanograins, with high-density intergranular and surface grain boundaries serving as the electrochemical reaction sites and facilitating mass transport. The conformal coating layer appears to have successfully suppressed the Sr outward diffusion and confined the Sr enriched layer to a ~ 2 nm interface perovskite phase between the coating layer and the LSCF grain surface. Moreover, this ultra-thin Sr enriched perovskite layer presumably possesses high oxygen vacancy and high ionic conductivity and further imposes tensile strain to the LSCF grain surfaces. With the combination of a conformal CoO x nanoionics, Sr enriched layer, and its strained interface, the ALD coating induced surface layer is estimated to have a conductivity of ~ 1.27x10 4 S/cm, which is over two orders magnitude of that from LSCF at 750 ºC.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2021

Systems and methods of decoupled hydrogen generation using energy-bearing redox pairs

Described herein are systems and methods of hydrogen generation and electrolyte regeneration as independent operations in separate redox flow cells. The operations can be decoupled by using an energy-bearing redox pair that electrochemically bears energy facilitating flexible, efficient hydrogen generation. In one example, the hydrogen generation redox flow cell can include a liquid, energy-bearing electrolyte solution in which at least one species of an energy-bearing redox pair is dissolved, to decouple the hydrogen evolution reaction from the reaction at the opposite electrode (e.g., the oxygen evolution reaction of conventional direct water electrolysis). Each species of the energy-bearing redox pair is associated with a standard electrode potential within the water electrolysis window.

Wang, Wei↗
DOE OSTI2022

Understanding and improving anode performance in an alkaline membrane electrolyzer using statistical design of experiments

The behavior of the oxygen-evolving positive electrode (i.e. anode) in the anion exchange membrane water electrolyzer (AEMEL) is complex and influenced by several factors. Very few studies have been performed to understand oxygen evolution reaction (OER) behavior by optimizing the individual factors that influence performance. Here, this study highlights the effects of catalyst loading, catalyst selection, porous transport layer (PTL) type and conductive additive content. The influence of each factor is elucidated through a design of experiments (DoE) approach with a full statistical analysis. Electrochemical data, alongside Pareto charts, parametric trends and their mutual interactions are discussed. This DoE approach is also helpful in making useful predictions and discovering new combinations to be tested. The end result was a high-performance AEMEL able to operate at a current density of 1.0 A/cm 2 at 1.80 V with IrOx OER and PtNi hydrogen evolution reaction (HER) catalysts using 0.3 M KOH fed to the anode. Even lower operating voltage was observed with PbRuOx catalyst at the anode, 1.64 V @ 1.0 A/cm 2 , though the cell decay rate was higher. Lastly, a IrOx/PtNi cell was stably operated continuously for 30 days (720 h) at 1.0 A/cm 2 . This study can serve as a guide for optimal electrode design with insights into component-performance compromises, which can aid in making design choices and performing techno-economic analyses.

08 HYDROGEN↗
DOE OSTI2020

Membrane electrode assembly

Membrane electrode assembly comprising oxygen evolution reaction catalyst disposed in gas distribution layer (100, 700) or between gas distribution layer (100, 700 and gas dispersion layer (200, 600). Membrane electrode assemblies described herein are useful, for example, in electrochemical devices such as a fuel cell.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2024

Ultra-stable and poison tolerant oxygen evolution activity enabled by surface In 2 O 3- x (OH) y of Co 3 In 2 S 2 large single crystals

Water is an earth-abundant source for clean hydrogen production via electrochemical water electrolysis (WE). However, the surface poisoning that occurs in aqueous electrolytes drastically deactivates the electrocatalytic performance of electrodes. Here, in this study, we report electrochemically formed In 2 O 3-x (OH) y on the surface of a large (1–1.5 mm long, 0.5–0.6 mm wide and 0.3–0.5 mm thick) single crystal of Weyl semimetal Co 3 In 2 S 2 (Co 3 In 2 S 2 /In 2 O 3-x (OH) y ) as an ultra-stable and poison tolerant electrode for the oxygen evolution reaction (OER) in 1 M KOH, addressing a bottleneck in WE. The OER activity of the powder form of Co 3 In 2 S 2 is limited by its aerophilic nature. Remarkably, the single-crystal electrodes maintained their high activity for a continuous operational period of 5 h in 1 M KOH electrolyte with/without 10 mM strong surface-poisoning ligands i.e., potassium cyanide, bipyridine, and ethylenediaminetetraacetate disodium salt. The electrodes exhibited stable OER activity for 1000 h at 100 mA cm -2 (1.73 V vs. RHE). The temperature-dependent OER polarization curves (10–70 °C) unambiguously revealed surface poisoning through the suppression of precatalytic Co-redox peaks on the bipyridine poisoned electrode, which led to the stabilization of surface Co-sites. The X-ray photoelectron spectroscopy analyses of pristine, poisoned and post-electrocatalytic single-crystal Co 3 In 2 S 2 electrodes revealed the existence of an In 2 O 3-x (OH) y surface phase, which could be the potential heterostructure for the origin of ultra-stable and poison tolerant OER activity.

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

Tuning Surface Acidity of Mixed Conducting Electrodes: Recovery of Si‐Induced Degradation of Oxygen Exchange Rate and Area Specific Resistance

Abstract Metal oxides are an important class of functional materials, and for many applications, ranging from solid oxide fuel/electrolysis cells, oxygen permeation membranes, and oxygen storage materials to gas sensors (semiconducting and electrolytic) and catalysts, the interaction between the surface and oxygen in the gas phase is central. Ubiquitous Si‐impurities are known to impede this interaction, commonly attributed to the formation of glassy blocking layers on the surface. Here, the surface oxygen exchange coefficient ( k chem ) is examined for Pr 0.1 Ce 0.9 O 2‐δ (PCO), a model mixed ionic electronic conductor, via electrical conductivity relaxation measurements, and the area‐specific resistance (ASR) by electrochemical impedance spectroscopy. It is demonstrated that even low silica levels, introduced by infiltration, depress k chem by a factor 4000, while the ASR increases 40‐fold and we attribute this to its acidity relative to that of PCO. The ability to fully regenerate the poisoned surface by the subsequent addition of basic Ca‐ or Li‐species is further shown. This ability to not only recover Si‐poisoned surfaces by tuning the relative surface acidity of an oxide surface, but subsequently outperform the pre‐poisoned response, promises to extend the operating life of materials and devices for which the catalytic oxygen/solid interface reaction is central.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2022

Electrical, thermal, and H 2 O and CO 2 poisoning behaviors of PrNi 0.5 Co 0.5 O 3-δ electrode for intermediate temperature protonic ceramic electrochemical cells

PrNi 0.5 Co 0.5 O 3-δ (PNC) exhibits adequate total electrical conductivity (~300 S/cm at 400–600 °C) and moisture has no significant effect on it. The thermal expansion coefficient of PNC is 17.6 × 10 –6 /K by dilatometry and 18.43 × 10 –6 /K by in situ XRD. PNC also demonstrates chemical stability against H 2 O and CO 2 . However, PNC symmetrical cell over proton-conducting BaZr 0.4 Ce 0.4 Y 0.1 Yb 0.1 O 3-δ (BZCYYb4411) electrolyte shows significant H 2 O and CO 2 poisoning when those are introduced into O 2 –N 2 mixture. In comparison, symmetrical cells with PNC electrode over the oxygen ion conducting Ce 0.9 Gd 0.1 O 2-δ (GDC) electrolyte show no H 2 O and CO 2 poisoning under similar conditions. Here, it is hypothesized that poisoning from H 2 O and CO 2 of the PNC proton conducting symmetrical cell is caused by their adsorption on the BZCYYb4411 electrolyte instead of PNC electrode. Such a hypothesis is supported by the H 2 O and CO 2 adsorption behaviors on PNC and BZCYYb4411 powder surfaces, as measured by temperature programmed desorption (TPD).

08 HYDROGEN↗
DOE OSTI2022

Building interface bonding and shield for stable Li-rich Mn-based oxide cathode

Implementation of Li-rich Mn-based oxide cathode with high-energy-density has been restrained by capacity/voltage degradation that results from irreversible lattice oxygen loss and structure rearrangements. To resolve these challenges, in this work, Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O 2 encapsulated by amorphous Co x B (CB-LRM) is rationally designed via autocatalytic plating for highly reversible cationic/anionic hybrid cathode material. Band coherency is ingeniously evoked by interface-reconstruction between bulk structure and amorphous coating layer, which lower the energy of O $2p$ states. Furthermore, this is associated with strengthened orbital hybridization of O $2p$-Mn $3d$ and increased formation energy of oxygen vacancy, which mitigates the lattice oxygen loss considerably. Additionally, interface shielding effects that protect electrode against electrolyte corrosion and the reduction of surface oxygen are also present with fully coverage of amorphous Co x B coating layer. As a result, the as-designed CBLRM cathode exhibits excellent cycle stability after 100 loops with only 0.154% per cycle capacity fade and improved voltage degradation. Given this, this work provides a potential avenue for rational design of lattice oxygen-based electrode materials with high-energy-density.

25 ENERGY STORAGE↗
DOE OSTI2024

Probing the active sites of oxide encapsulated electrocatalysts with controllable oxygen evolution selectivity

Electrocatalysts encapsulated by nanoscopic overlayers can control the rate of redox reactions at the outer surface of the overlayer or at the buried interface between the overlayer and the active catalyst, leading to complex behavior in the presence of two competing electrochemical reactions. This study investigated oxide encapsulated electrocatalysts (OECs) comprised of iridium (Ir) thin films coated with an ultrathin (2–10 nm thick) silicon oxide (SiO x ) or titanium oxide (TiO x ) overlayer. The performance of SiO x |Ir and TiO x |Ir thin film electrodes towards the oxygen evolution reaction (OER) and Fe(II)/Fe(III) redox reactions were evaluated. An improvement in selectivity towards the OER was observed for all OECs. Overlayer properties, namely ionic and electronic conductivity, were assessed using a combination of electroanalytical methods and molecular dynamics simulations. SiO x and TiO x overlayers were found to be permeable to H 2 O and O 2 such that the OER can occur at the MO x |Ir (M = Ti, Si) buried interface, which was further supported with molecular dynamics simulations of model SiO 2 coatings. In contrast, Fe(II)/Fe(III) redox reactions occur to the same degree with TiO x overlayers having thicknesses less than 4 nm as bare electrocatalyst, while SiO x overlayers inhibit redox reactions at all thicknesses. This observation is attributed to differences in electronic transport between the buried interface and outer overlayer surface, as measured with through-plane conductivity measurements of wetted overlayer materials. These findings reveal the influence of oxide overlayer properties on the activity and selectivity of OECs and suggest opportunities to tune these properties for a wide range of electrochemical reactions.

08 HYDROGEN↗
DOE OSTI2025

Exsolution of NiCo alloys over Ruddlesden-Popper perovskite for mild electrochemical synthesis of ammonia on protonic ceramic electrochemical cells

Ammonia synthesis from renewable energies on protonic ceramic electrochemical cells (PCECs) shows great potential. The primary challenges in ammonia synthesis on PCECs include sluggish catalytic activity, competition from the hydrogen evolution reaction, and unsatisfactory durability of the cathode, which is the active site of ammonia generation. Here, in this study, we report an elaborate design of the cathode with an intended formula of Pr 4 Ni 1.79 Co 1.2R u 0.01 O 10-δ , where NiCo alloy nanoparticles are exsolved from Ruddlesden-Popper perovskite substrates after the reduction in 5 % H 2 /Ar at 400 °C for 1 h, for electrocatalysis of the nitrogen reduction reaction to ammonia. The host material Pr 4 Ni 1.8 Co 1.2 O 10-δ with embeddable layered structure and stability was deliberately chosen to fix the Ru cation and maximize the catalytic activity of NiCo. Also, density functional theory calculations suggest that Ru doping provides an optimal balance between structural stability and redox activity, facilitating the controlled exsolution of NiCo nanoparticles and enhancing catalytic performance. As a result, the composite electrode with exsolved NiCo alloy and abundant oxygen vacancies on fuel-electrode-supported PCECs achieves a superior electrochemical activity towards ammonia synthesis: a peak ammonia formation rate of 27.84 μg h −1 cm −2 and excellent Faradaic efficiencies of 62.6 % at 350 °C.

30 DIRECT ENERGY CONVERSION↗