SEARCH · Engineering Papers
Results for “oxygen electrode”
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Boosting energy efficiency of Li-rich layered oxide cathodes by tuning oxygen redox kinetics and reversibility
In developing electrode materials for next-generation Li-ion batteries, significant efforts have been given to the energy, power density and cycling stability, with much less (if any) attention paid to the energy efficiency – arguably, the most important practical measure for large-scale applications. This is particularly true for the oxygen-redox active electrodes, such as Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 , the notorious energy-inefficient cathode that has an extremely high capacity but comes with large voltage hysteresis and voltage decay. Herein, we report the rational design of an energy-efficient Li-rich layered cathode along with high energy, power density and cycling stability enabled by tuning oxygen redox activity. Specifically, the target material Li 1.12 Ni 0.22 Co 0.13 Mn 0.52 O 2 exhibits an ultrahigh energy efficiency at 1 C (90.6%), high capacity (> 200 mAh g -1 ) with 98.9% retention and less than 150 mV decay at the extended 200 cycles. Overall, through direct comparison between the material and Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 , we show that the compositional change, although slightly, greatly improves the oxygen redox kinetics and reversibility, thereby boosts energy efficiency. The findings offer a strategy to narrow the gap between scientific interest and practical application of oxygen-redox chemistry.
Oxygen and Proton Transport in Flooded Graphene Pores with N-Dopants and Defects
Reactant transport is an important consideration in the design of ideal electrode structures. For the oxygen reduction reaction catalyzed by Pt/C in proton exchange membrane fuel cell cathodes, O 2 and H + delivery to Pt surfaces and H 2 O transport away are required. Some Pt nanoparticles may only be accessible via micropores that are too small for ionomer molecules to enter, possibly requiring flooding for H + transport. Here, to test if these “buried” Pt particles can play a role in activity through this proposed transport mechanism, we have performed atomic-scale simulations based on reactive force field molecular dynamics with an emphasis on confinement below 20 Å. Diffusion coefficients as a function of the molar concentration and local environment have been evaluated in water domains confined in two-dimensional graphene nanochannels of various channel heights representing a morphological model for micropores in proton exchange fuel cell cathodes. Our study shows that local atomic-scale structures can strongly modify H + , O 2 , and H 2 O transport rates in flooded micropores less than 20 Å in size. We find that there is a critical crossover in diffusion behavior around the 20 Å spacing with larger pores having bulk-like diffusion properties and confinement below 20 Å monotonically decreases diffusion rates. As pore size decreases, we observe locally dispersed water regions that ultimately strand reactants from long-distance transport. These findings suggest that flooded micropores may in fact be viable transport pathways for relevant reactants and products if the pore walls on opposite sides remain separated by ≥10 Å separation. Furthermore, the confinement effect is so strong that N-doping and C-vacancy defects in the C pore wall have only a minimal impact on diffusion rates and their effects are counterintuitively more apparent at larger spacings. These findings provide valuable insight regarding cathode performance and the role “stranded” catalyst particles may play in fuel cell cathodes.
Surface and Bulk Oxygen Kinetics of BaCo 0.4 Fe 0.4 Zr 0.2-X Y X O 3-δ Triple Conducting Electrode Materials
Triple ionic-electronic conductors have received much attention as electrode materials. In this work, the bulk characteristics of oxygen diffusion and surface exchange were determined for the triple-conducting BaCo 0.4 Fe 0.4 Zr 0.2-X Y X O 3-δ suite of samples. Y substitution increased the overall size of the lattice due to dopant ionic radius and the concomitant formation of oxygen vacancies. Oxygen permeation measurements exhibited a three-fold decrease in oxygen permeation flux with increasing Y substitution. The DC total conductivity exhibited a similar decrease with increasing Y substitution. These relatively small changes are coupled with an order of magnitude increase in surface exchange rates from Zr-doped to Y-doped samples as observed by conductivity relaxation experiments. The results indicate that Y-doping inhibits bulk O 2- conduction while improving the oxygen reduction surface reaction, suggesting better electrode performance for proton-conducting systems with greater Y substitution.
Improving charge transport in integrated MoO 3 /C electrode materials for water-in-salt energy storage systems by incorporating oxygen vacancies
Improvements in the charge storage properties of α-MoO 3 used as an electrode with a 30m ZnCl 2 water-in-salt electrolyte have been achieved by enhancements in electron and ion transport enabled by an inventive synthesis route. Electron transport was improved through the integration of MoO 3 with dopamine-derived carbon via a chemical preintercalation route, and enhanced ion transport was achieved by incorporating oxygen vacancies in MoO 3 structure through ethanol 2 reduction under hydrothermal conditions. Here, the presence of carbon was confirmed by corresponding D and G bands observed in Raman spectroscopy measurements. The presence of oxygen vacancies was proven through correlated XPS, TGA, Raman spectroscopy and XRD analyses, with the introduction of oxygen vacancies leading to an expanded interlayer region. Four-point probe measurements provided evidence of increased electronic conductivity due to the incorporation of carbon, and cyclic voltammetry-based charge storage mechanism analyses revealed increases in ion transport kinetics due to oxygen vacancy formation. Tuning the oxygen vacancy concentration is critical, as excessive concentrations of these point defects leads to structural instability and poor capacity retention. This work demonstrates the combined potential of carbon and oxygen vacancies in moderate concentrations to enhance the charge storage properties of transition metal oxides. The strategies developed in this study offer a path to the development of promising materials for high-rate, high-capacity, and long-duration electrochemical energy storage technologies.
Towards controlling the reversibility of anionic redox in transition metal oxides for high-energy Li-ion positive electrodes
Transition metal d-states and oxygen p-states overlap and oxygen lattice integrity dictates the oxygen redox reversibility in metal substituted Li 2 RuO 3 positive electrodes for Li-ion batteries.
Morphology engineering of iridium electrodes via modifying titanium substrates with controllable pillar structures for highly efficient oxygen evolution reaction
Nowadays, Ti is the well-chosen anode substrate material for proton exchange membrane electrolyzer cells (PEMECs) and modifications of the substrate surfaces are essential for the fabrication of highly efficient electrodes. Herein, we introduce the morphology engineering of Ir/Ti electrodes with different acid treatments of hydrochloric acid (HCl) and oxalic acid (OA), and the comparative benefits of these two acid treatment methods are studied from the aspects of their impacts on the morphology, interfacial contact resistance (ICR), and oxygen evolution reaction (OER) performances of resultant electrodes. Notably, compared to the flat surface from OA treatment, Ti substrates with the pillar structure could be successfully achieved via HCl etching. Further, the HCl and the oxalic acid (OA) treatments would reduce the interfacial contact resistance (ICR) to 15.2% and 5.5% of the pristine Ti substrate at 1.38 MPa, respectively. By iridium electrodeposition on Ti substrates, Ir/Ti electrodes with different catalyst loadings are fabricated. With similar low-loadings of about 0.05 mgIr cm –2 , an Ir/Ti electrode with HCl treated substrate exhibits a lower overpotential of ~283 mV at 10 mA cm –2 current density than 305 mV from OA treatment, due to the boosted reaction areas from HCl treatment.
Nanoporous Iridium Nanosheets for Polymer Electrolyte Membrane Electrolysis
The growth of the hydrogen economy is predicated on advancements in electrochemical energy technologies, with water electrolysis as a key component to the technological portfolio. Much of the focus on anode catalyst development for polymer electrolyte membrane water electrolyzers (PEMWE) is centered on activity as controlled by compositional and morphological impacts on reactant/intermediate/product adsorption. However, the effectiveness of this strategy is found to be limited upon integration of these materials into PEMWE membrane electrode assemblies (MEA). Regardless of catalyst activity, the combination of electrode inhomogeneity, ionomer integration, and high density of oxide-oxide interfaces yields significant performance losses associated with poor catalytic electrode conductivity. Here many of these limitations are addressed through the development of a unique catalyst morphology composed of nanoporous Ir nanosheets (npIr(x)-NS) that exhibit high catalytic activity for the anodic oxygen evolution reaction and superior electrode electronic conductivity in comparison to a commercial IrO2 nanoparticle catalyst. The utility of the npIr(x)-NS is demonstrated through incorporation into PEMWE MEAs where their performance exceeds that of commercial catalyst coated membranes at loadings as low as 0.06 mg(Ir) cm(-2) while exhibiting a negligible loss in performance following 50 000 accelerated stress test cycles.
Effect of Anesthesia Gases on the Oxygen Reduction Reaction
Not Available
Investigation of oxygen evolution reaction with Ni foam and stainless-steel mesh electrodes in alkaline seawater electrolysis
We report alkaline seawater electrolysis is a promising method for hydrogen production; however, little progress has been made in investigating the substrates for oxygen evolution reaction (OER) electrocatalysts. Ni foam and stainless-steel mesh (SS mesh) were investigated systematically for OER in alkaline seawater electrolysis in this work. The overpotentials and Tafel slopes with SS meshes are smaller than Ni foams, and it also exhibits excellent stability. Interestingly, the performance of the SS mesh even outperforms various non-noble metal electrocatalysts and is comparable to commercial RuO2 and IrO2. The corrosion conditions of Ni foam and SS mesh electrodes were studied and revealed. Furthermore, the electrochemically active surface area (ECSA) of Ni foam is 12 times higher than SS mesh in the same geometric area, indicating the electrochemical activity of SS mesh is much superior to Ni foam. This work expands on promising substrates for alkaline seawater electrolysis, with cost and performance advantages.
Electrochemical cells for hydrogen gas production and electricity generation, and related systems and methods
An electrochemical cell comprises a first electrode, a second electrode, and a proton-conducting membrane between the first electrode and the second electrode. The first electrode comprises Pr(Co 1-x-y-z , Ni x , Mn y , Fe z )O 3-δ , wherein 0≤x≤0.9, 0≤y≤0.9, 0≤z≤0.9, and δ is an oxygen deficit. The second electrode comprises a cermet material including at least one metal and at least one perovskite. Related structures, apparatuses, systems, and methods are also described.
Equivalent Circuit Modeling for Carbon Nanotube Schottky Barrier Modulation in Polarized Gases
We study the carbon nanotube Schottky barrier at the metallic electrode interface in polarized gases using an equivalent circuit model. The gas-nanotube interaction is often weak and very little charge transfer is expected [l]. This is the case with'oxygen, but the gas-electrode interaction is appreciable and makes the oxygen molecules negatively charged. In the closed circuit condition, screening positive charges appear in the nanotube as well as in the electrode, and the Schottky barrier is modulated due to the resultant electrostatic effects [2]. In the case of ammonia, both the gas-nanotube and gas-electrode interactions are weak, but the Schottky barrier can still be modulated since the molecules are polarized and align in the preferred orientation within the gap between the electrode and nanotube in the open circuit condition (dipole layer formation). In the closed circuit condition, an electric field appears in the gap and strengthens or weakens the preferred dipole alignment reflecting the nanotube Fermi level. The modulation is visible when the nanotube depletion mode is involved, and the required dipole density is as low as 2 x 10(exp 13) dipoles/sq cm, which is quite feasible experimentally,
Characterization of recombination Quarterly report, Jun. 9 - Sep. 9, 1966
Oxygen recombination and control of electrodes for spacecraft nickel-cadmium cells
Effect of porous transport layer properties on the anode electrode in anion exchange membrane electrolyzers
Anion exchange membrane water electrolyzers (AEMELs) have recently received significant attention due to their potential advantages over existing commercial water electrolysis technologies. However, AEM electrolyzers have not yet met performance and durability targets. One of the critical components in achieving high AEMEL performance is the porous transport layer (PTL) which serves many critical functions in the oxygen evolution reaction (OER) electrode. In this study, several OER PTL attributes were investigated, including: material of construction, fabrication method, feature size, porosity/density, and thickness. It was found that higher porosity helped facilitate multiphase (O 2 , H 2 O, etc.) transport; however, as the porosity increased, the catalyst layer adhesion to the PTL decreased, the contact resistance with the bipolar plate increased and the cell operating voltage increased. It was found that nickel-based PTLs allowed for lower operating voltages than similarly-structured stainless steel PTLs. Improved operating voltages were achieved with both fiber felts and sintered structures by porosity optimization. Furthermore, an increase in thickness did not affect transient voltage response, however, it had a negative effect on performance stability. As a result, the experimental findings presented here provide important insights for development of PTL materials and structures for efficient and low-cost water electrolysis.
Non-planar platinum group metal-free fuel cell cathodes for enhanced oxygen transport and water rejection
Proton exchange membrane fuel cells (PEMFC) with cathodes using platinum group metal-free (PGM-free) catalysts could significantly reduce costs, but the lower volumetric oxygen reduction reaction (ORR) activity requires thick electrodes that suffer from liquid water flooding and increased oxygen transport resistance. To address these challenges, we developed a 3D gas diffusion electrode (GDE) architecture to enhance liquid water removal through the diffusion media and reduce cathode saturation. The cathode features a uniform catalyst layer adjacent to the membrane for high ORR activity and then pillars of the hydrophilic catalyst layer that pass through the microporous layer (MPL), providing a low capillary pressure barrier pathway to the carbon fiber paper layer and channel. The non-planar cathode also increases the interfacial area between the catalyst layer and hydrophobic MPL for a greater fraction of the cathode with high O 2 concentration. Our studies included parametric experimental study of the pillar density to identify the optimum pitch between pillars. Our measurements show significant improvements in the mass transport region of the polarization curve with 3D structured electrodes leading to an 8% increase in maximum current density, 19% increase in maximum power density, and 16% increase in current density at 0.67 V with air.
Pt–Co truncated octahedral nanocrystals: a class of highly active and durable catalysts toward oxygen reduction
We report a facile and scalable synthesis of Pt–Co truncated octahedral nanocrystals (TONs) by employing Pt(acac) 2 and Co(acac) 2 as precursors, together with CO molecules and Mn atoms derived from the decomposition of Mn 2 (CO) 10 as a reductant and a {111} facet-directing agent, respectively. Both the composition and yield of the Pt–Co TONs could be varied through the introduction of CHCl 3 . When tested at 80 °C using membrane electrode assembly (MEA), the 4 nm Pt 2.6 Co TONs gave a mass activity of 294 A g Pt –1 at beginning-of-life (BOL) and it increased to 384 A g Pt –1 during recovery cycles. The mass activity at BOL only dropped by 24% after 30 000 voltage cycles at end-of-life (EOL) in a metal dissolution accelerated stress test. The Pt 2.6 Co/C catalyst outperformed the commercial TKK Pt 3 Co/C (230 A g Pt –1 at BOL and 40% loss after 30 000 cycles at EOL) in terms of both activity and durability. Our systematic analysis suggested that the enhancement in activity can be attributed to the combination of small, uniform size and well-defined {111} facets. This new class of catalysts holds promise for applications in proton-exchange membrane fuel cells.
Machine learning-guided discovery of gas evolving electrode bubble inactivation
The adverse effects of electrochemical bubbles on the performance of gas-evolving electrodes are well known, but studies on the degree of adhered bubble-caused inactivation, and how inactivation changes during bubble evolution are limited. We study electrode inactivation caused by oxygen evolution while using surface engineering to control bubble formation. We find that the inactivation of the entire projected area, as is currently believed, is a poor approximation which leads to non-physical results. Using a machine learning-based image-based bubble detection method to analyze large quantities of experimental data, we show that bubble impacts are small for surface engineered electrodes which promote high bubble projected areas while maintaining low direct bubble contact. We thus propose a simple methodology for more accurately estimating the true extent of bubble inactivation, which is closer to the area which is directly in contact with the bubbles.
Critical Assessment of Electronic Structure Descriptors for Predicting Perovskite Catalytic Properties
The discovery and design of materials which can efficiently catalyze the oxygen reduction and evolution reactions at reduced temperatures is important for facilitating the widespread adoption of fuel cell and electrolyzer technologies. Numerous studies have produced correlations between catalytic properties, such as oxygen surface exchange or electrode area specific resistance (ASR), and properties of the catalyst material. However, correlations have historically been limited in scope (e.g., using only a few materials or at a single temperature) and it has been difficult to provide detailed assessments of their robustness. Here, in this study, we assess the ability of the O p-band center electronic structure descriptor, obtained from density functional theory (DFT) calculations, to correlate with oxygen surface exchange rates, diffusivities, and area specific resistances for a large database of perovskite oxide catalytic properties. By data mining the literature, we obtain 747 catalytic property value data points spanning 299 unique perovskite compositions from 313 studies. We assess linear correlations of each property with the O p-band center and find generally modest correlations that are qualitatively useful (prediction mean absolute errors of about 0.5 log units are typical), where the correlations are improved at higher temperatures (e.g., 800 °C vs. 500 °C) and significantly improve when considering fits to the subset of materials which have multiple independent measurements. These findings suggest that the spread of property data is significantly influenced by experimental uncertainty, and subsequent measurements of additional materials will likely improve the O p-band center correlations.