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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Electrochemical Residence Time Distribution as a Diagnostic Tool for Redox Flow Batteries

The fluid dynamic and electrochemical performance of redox flow batteries (RFBs) stems from the relationship between the flow field and the porous electrode, whose interplay determines how active species move and react during device operation. While characterization techniques, such as residence time distribution, offer insights into species mobility within a reactive volume for a traditional chemical reactor, electrochemical reactors also enable simultaneous measurement of the redox reactions, unlocking another dimension of analysis. Herein, we demonstrate how potentiodynamic measurements, using injections of electrolyte examined through moment analysis, can provide electrode-specific performance scaling relationships across a matrix of carbon paper and cloth electrodes with flow through and interdigitated flow fields. We further combine experimental campaigns with multiphysics simulations to demonstrate how electrode surface area can be estimated with this technique, which we then validate with activated and unactivated commercial carbon cloth electrodes. These studies reveal the multiscale observations that potentiodynamic measurements afford, augmenting existing electrochemical techniques for holistic electrochemical reactor diagnostics.

Electrochemistry↗
DOE OSTI2020

Unexpected electrochemical behavior of an anolyte redoxmer in flow battery electrolytes: solvating cations help to fight against the thermodynamic–kinetic dilemma

Redoxmers are redox-active molecules that can store energy in electrolytes for redox flow batteries (RFBs), and their electrochemical properties are significantly affected by the choice of supporting electrolytes. Herein, we use 2,1,3-benzothiadiazole (BzNSN) as a model system to scrutinize the supporting electrolyte impact. By systemically varying the components of supporting salts, BzNSN not only shows substantial redox potential shifts but also exhibits varying electrochemical stabilities. Specifically, changing the size of cations can effectively alter the coordination between the supporting salt and BzNSN species. From Li + , Na + , K + , to NEt 4 + , the redox potential of BzNSN shifts negatively, from -1.63 V to -1.82 V vs. Ag/Ag + . Molecular dynamics and density functional theory simulations revealed that smaller cations, like Li + , are closer to the charged BzNSN when coordinated, implying stronger coordination, while larger cations, like K + and NEt 4 + , are farther away. Interestingly, the large cation electrolytes also lead to much improved electrochemical stability, evidenced by the extraordinarily enhanced kinetic lifetime from electron paramagnetic resonance measurement. This study demonstrates the first example of tuning an anolyte redoxmer toward a concurrent improvement of lowered redox potentials AND enhanced calendar lives via solvation means, which is usually constrained by the thermodynamic–kinetic relation.

2,1,3-benzothiadiazole↗
DOE OSTI2022

The Poor Academic’s DC-Offset for Reversing Polarity in Electrochemical Cells: Application to Redox Flow Cells

We provide a simple and inexpensive manual DC-offset method for extending the accepted voltage range of a battery cycler to negative voltages, without interfering with the actual operation of the electrochemical cell under the test or exceeding the voltage specs of the battery cycler instrument. We describe the working principles of the method and validate the proposed setup by operating short-term and long-term redox flow battery cycling using compositionally symmetric cell, with open-circuit voltage of zero, and full cell configurations. The method can be used to extend the capability of battery cycler instrumentation to operate any electrochemical cell that requires the polarity to be reversed during operation. Applications include cycling of other symmetric cells (e.g., Li-ion cells), implementation of polarity reversal steps for rejuvenation of electroactive species or rebalancing electrochemical cells, and alternating polarity for electrochemical synthesis.

25 ENERGY STORAGE↗
DOE OSTI2024

Flow field design for zero-gap microbial electrolysis cells using synthetic and real wastewater

Increasing performance in microbial electrolysis cells (MECs) requires the development of optimized reactor configurations with minimal internal resistance and capable to operate with real wastewater. Here, the impact of two different flow fields (serpentine and circular) was examined in zero-gap MECs with synthetic and real wastewaters. The serpentine flow field enabled a uniform distribution of the electrolyte in the anode chamber, resulting in larger current densities at lower flow rates compared to the circular flow field. Electrochemical tests using synthetic media with high buffer capacity revealed more stable and higher performance with the serpentine flow field compared to the circular flow path, producing larger current density (23.7 ± 0.8 A/m 2 vs 21.9 ± 5.6 A/m 2 ), hydrogen production rate (75.8 ± 4.1 L/L-d vs 54.3 ± 2.4 L/L-d), cathodic coulombic efficiency (>91 % vs >50 %), and an overall lower internal resistance (12.5 ± 0.5 mΩm 2 vs 14.8 ± 3.7 mΩm 2 ). Continuous operation for over 30 days with real wastewater indicated higher tolerance of the MECs with serpentine flow field toward media with large concentration of suspended solids, producing a current density of 5.4 ± 1.1 A/m 2 and a hydrogen production rate of 22.2 ± 6.2 L/L-d. Furthermore, the results presented here underscore the importance of reactor design and architecture in optimizing MEC performance for hydrogen production from liquid wastes.

flow path↗
DOE OSTI2023

Colocalized Raman spectroscopy – scanning electrochemical microscopy investigation of redox flow battery dialkoxybenzene redoxmer degradation pathways

Non-aqueous redox flow batteries offer high voltages for grid-level energy storage technologies. However, decomposition of the redoxmers - redox-active molecules that make up the anolyte and catholyte in the negative and positive cell compartments - is an important challenge to overcome for long-term storage. Here, we present a spectroelectrochemical study of the catholyte candidate 2,3-dimethyl-1,4-dialkoxybenzene (C7) and its decomposition mechanisms in the presence of a model nucleophilic base, pyridine. We utilize colocalized Raman microscopy and scanning electrochemical microscopy (Raman-SECM) to quantify the chemical rates of decom-position and qualitatively identify the reaction intermediates and products. A detailed study on how the Raman-SECM parameters (electrode distance, substrate electrode, and laser focal height) influence the Raman signal of the charged catholyte C7 ∙+ is presented. Using optimized conditions, we monitored the deprotonation of C7 ∙+ via Raman spectroscopy and the subsequent hydrogen abstraction from solvent molecules to regenerate C7 via electrochemistry. Finite element modeling was used to fit electrochemical and spectroscopic data, quantifying the deprotonation rates as k dep = 2000 and 700 L mol -1 s -1 and abstraction rates as k abs = 0.5 and 0.2 s - 1 in propylene carbonate and acetonitrile solvents, respectively. Our results show the value of spatiotemporal reso-lution in evaluating the chemical and electrochemical behavior of materials for redox flow batteries.

25 ENERGY STORAGE↗
DOE OSTI2022

Mechanistic Study of Controlled Zinc Electrodeposition Behaviors Facilitated by Nanoscale Electrolyte Additives at the Electrode Interface

Nanoparticle organic hybrid materials (NOHMs) are liquid-like materials composed of an inorganic core to which a polymeric canopy is ionically tethered. NOHMs have unique properties including negligible vapor pressure, high oxidative thermal stability, and the ability to bind to reactive species of interest due to the tunability of their polymeric canopy. This makes them promising multifunctional materials for a wide range of energy and environmental technologies, including electrolyte additives for electrochemical energy storage (e.g., flow batteries) and the electrochemical conversion of CO 2 to chemicals and fuels. Due to their unique transport behaviors in fluid systems, an understanding of the near-electrode surface behavior of NOHMs in electrolyte solutions and their effect on electrochemical reactions is still lacking. In this work, the complexation of zinc (Zn) by NOHMs with an ionically tethered polyetheramine canopy (HPE) (NOHM-I-HPE) was studied using attenuated total reflectance Fourier transform infrared and Carbon-13 nuclear magnetic resonance spectroscopy. Additionally, various electrochemical techniques were employed to discern the role of NOHM-I-HPE during zinc electrodeposition, and the results were compared to those of the electrochemical system containing untethered HPE polymers. Our findings confirmed that NOHM-I-HPE and HPE reversibly complex zinc in the aqueous electrolyte. NOHM-I-HPE and HPE were found to block some of the electrode active sites, reducing the overall current density during electrodeposition, while facilitating the formation of smooth zinc deposits, as revealed by surface imaging and diffraction techniques. Observed variations in the current density responses and the degree of passivation created by the NOHM-I-HPE and HPE adsorbed on the electrode surface revealed that their different packing behaviors at the electrode–electrolyte interface influence the zinc deposition mechanism. The presence of the nanoparticle and ordering offered by the NOHMs as well as the structured conformation of the polymeric canopy allowed the formation of void spaces and free volumes for enhanced transport behaviors. Furthermore, these findings provided insights into how structured electrolyte additives such as NOHMs can allow for advancements in electrolyte design for controlled deposition of metal species from energy-dense electrolytes or for other electrochemical reactions.

25 ENERGY STORAGE↗
DOE OSTI2022

Electrochemical Mitigation of Corrosion in Molten Chloride Salts During CSP Plant Operation

We are designing an electrochemical flow-cell for removal of corrosive impurities from molten chloride salt Gen3 Concentrating Solar Power (CSP) plants during plant operation. Corrosive impurities will inevitably form in molten chloride salts upon exposure to air and moisture. We previously showed that even small amounts of these impurities, especially MgOHCl, will be detrimental in Gen3 CSP plants, necessitating prohibitively expensive containment alloys and frequent replacement of corroded components. Pre-purification of salt with Mg metal at temperatures above 650 degrees C is the current method for removing corrosive impurities from chloride salts before they are introduced to CSP systems. However, this is not a suitable method for impurity removal during plant operation. First, this method will produce MgO particulates which will damage plant components. Second, Mg metal is solid at the low temperature point (500 degrees C), so the purification will not proceed at a fast rate. At the high temperature point, Mg is soluble. In this case, fast purification may proceed, but dissolved metal is likely to precipitate out in cold-temperature point components, causing damage. In contrast, our electrochemically driven method allows fast Mg-based purification to proceed at the low temperature point, without formation of harmful particulates and without the risk of Mg metal precipitation. This novel approach is inspired by electrorefining techniques that are widely employed in industrial metallurgy for removal of impurities from metals. Impurities in the incoming molten salt will be reduced to inert MgO at the cathode, which can be removed by periodically washing the cell with acid. Simultaneously, Mg dissolution at the anode will ensure salt composition is maintained, with no net removal of Mg2+. We have validated this electrochemical approach at lab scale under static conditions with batch rectors. Furthermore, we have performed analytical modeling and technoeconomic analysis to produce a preliminary engineering design for the purification flow cell.

CSP↗
DOE OSTI2024

Importance of High Valence Element Nb in Ni-Rich Layered Cathodes for High-Voltage Lithium-Metal Batteries

Ni-rich layered cathode materials have attracted extensive attention due to their higher energy density and technological maturity in commercialization. As the nickel content is raised, especially surpassing 80%, the increased energy density comes with the tradeoff of diminished thermal stability and increased electrochemical structural instability of the cathode. Compared with Co, Al, B, and Ta, the introduction of high valence element Nb significantly improved the electrochemical cycling, delivering a capacity of 202 mAh/g, corresponding to a capacity retention of 92% after 200 cycles tested at 45 °C. Further, the ex situ differential scanning calorimetry and in situ isothermal microcalorimetry demonstrate that the Nb-modified cathode has the potential to enhance the safety of ultrahigh nickel (Ni) NMCs and displays remarkable resilience to extensive cycling by inhibiting high-temperature decomposition reactions and exhibiting a lower heat flow during electrochemical cycling.

25 ENERGY STORAGE↗
DOE OSTI2021

Decomposition pathways and mitigation strategies for highly-stable hydroxyphenazine flow battery anolytes

Aqueous organic redox flow batteries are a promising technology for large-scale energy storage. The stability of the redox active organic molecules is increasingly being recognized as one of the major hurdles. Upon extended flow battery cycling, 7,8-dihydroxyphenazine-2 sulfonic acid (DHPS) undergoes desulfonation and reduction of a phenolic C–O bond to yield a mixture of 7/8-hydroxyphenazine-2-sulfonic acid, as well as hydrogenation of the aromatic ring system. Density functional theory (DFT) analysis of the charged DHPS, its ring-hydrogenated products, and variably substituted hydroxy phenazines has led to the development of a series of dihydroxylated phenazine isomers which provide insight into the effects of substitution pattern on solubility and stability. Seven dihydroxyphenazine (DHP) isomers were synthesized and their solubilities, electrochemical properties, flow battery cycling performance, and degradation pathways have been investigated. Based on theoretical and experimental results, hydroxyl substitution at the 1, 4, 6 and 9 positions yields highly stable derivatives, while substitution at the 2, 3, 7, and 8 positions results in unstable derivatives. Flow cells of 1,4- and 1,6-DHPs coupled with ferro/ferricyanide achieved high stabilities, with temporal capacity loss of 0.029 and 0.031% per day, respectively. Decomposition of 1,8- and 2,7-DHPs were found to arise from irreversible hydrogen rearrangement (tautomerization), yielding redox-inactive species. These results provide a detailed understanding of decomposition pathways and mitigation strategies for phenazine-based anolytes, and can provide general design guidelines for the development of stable redox-active organics.

25 ENERGY STORAGE↗
DOE OSTI2021

Toward Optimizing Electrospun Nanofiber Fuel Cell Catalyst Layers: Polymer–Particle Interactions and Spinnability

We investigate the effect of the poly(acrylic acid) (PAA) carrier polymer concentration on the microstructure and rheological properties of catalyst inks for electrospun polymer–electrolyte membrane fuel-cell catalyst layers. Characterization of an ink microstructure using oscillatory shear rheology showed that the catalyst particles (platinum on carbon) are significantly agglomerated in the absence of PAA or an ionomer. Both the ionomer and PAA promoted the stability of the particles against agglomeration via electrosteric stabilization by adsorbing onto the particle surface. Increasing the PAA concentration increased the stability of the particles (or reduced the agglomerated structure) due to increasing PAA coverage onto the free surface area of the particles. However, beyond a certain increase in concentration, PAA was found to predominantly remain as an excess free polymer in the ink due to an insufficient free/available surface area on the particles for further PAA coverage. Extensional rheology measurements demonstrated that PAA enhances the extensional viscosities of the inks. Consequently, increasing the PAA concentration in the ink promoted the evolution of uniform nanofibers. However, beyond a certain concentration, a significant increase in the shear viscosities of the inks led to defective fiber morphologies because of the onset of flow instabilities. Electrochemical performance comparisons between catalyst layers with different PAA concentrations showed maximum performance at the PAA concentration that led to the least agglomerated structure of the catalyst, most uniform fiber morphologies, and low concentrations of free (non-adsorbing) PAA in the electrode. These results provide a rationale for optimization of electrospun catalyst nanofibers for both spinnability and electrochemical performance.

25 ENERGY STORAGE↗
DOE OSTI2024

Aqueous redox flow battery electrolytes with high chemical and electrochemical stability, high water solubility, low membrane permeability

The invention features redox flow batteries and compound useful therein as negolytes or posolytes. The batteries and compounds are advantageous in terms of being useable in water solutions at neutral pH and have extremely high capacity retention. Suitable negolytes are diquaternized bipyridines, suitable posolytes are water-soluble ferrocene derivatives.

Gordon, Roy G.↗
DOE OSTI2024

Micro-architected flow through electrodes for energy storage

Disclosed are electrochemical reactors with electrodes that have variable porosity across the electrode. The electrodes are designed and micro-architected to have variable porosity and 3D flow. In one aspect, an electrochemical cell apparatus is disclosed. The apparatus includes an electrochemical vessel and an electrochemical fluid contained in the electrochemical vessel. The apparatus further includes a porous electrode submerged in the electrochemical fluid in the electrochemical vessel, the porous electrode having different porosities in different areas of the porous electrode. The different porosities inhibit electrochemical fluid flow and increase electrical conductivity in first areas of the porous electrode with decreased porosity compared to second areas, and enable increased electrochemical fluid flow and decrease electrical conductivity in the second areas of the porous electrode with increased porosity compared to the first areas.

Beck, Victor Alfred↗
DOE OSTI2021

Computational design of microarchitected porous electrodes for redox flow batteries

Porous electrodes are used as the core reactive component across electrochemical technologies. In flowing systems, controlling the fluid distribution, species transport, and reactive environment is critical to attaining high performance. However, conventional electrode materials like felts and papers provide few opportunities for precise engineering of the electrode and its microstructure. To address these limitations, architected electrodes composed of unit cells with spatially varying geometry determined via computational optimization are proposed. Resolved simulation is employed to develop a homogenized description of the constituent unit cells. These effective properties serve as inputs to a continuum model for the electrode when used in the negative half-cell of a vanadium redox flow battery. Porosity distributions minimizing power loss are then determined via computational design optimization to generate architected porosity electrodes. The architected electrodes are compared to bulk, uniform porosity electrodes and found to lead to increased power efficiency across operating flow rates and currents. The design methodology is further used to generate a scaled-up electrode with comparable power efficiency to the bench-scale systems. Finally, the variable porosity architecture and computational design methodology presented here thus offers a novel pathway for automatically generating spatially engineered electrode structures with improved power performance.

25 ENERGY STORAGE↗
DOE OSTI2021

High-speed characterization of two-phase flow and bubble dynamics in titanium felt porous media for hydrogen production

Bubble dynamics and two-phase flow phenomena are closely related to the performance of proton exchange membrane electrolyzer cells (PEMECs). This paper reports an in-situ study of the oxygen bubble behavior and associated multiphase evolutions in the anode side of PEMECs with titanium (Ti) felt liquid gas diffusion layers (LGDLs) by a high-speed visualization system. The micro oxygen bubble dynamics was captured and analyzed at different locations and virous operating conditions. The results show that the bubble detachment frequency and detachment diameter greatly increase with the operating current density. Additionally, they are significantly impacted by the local pore structure and morphology of Ti felt LGDLs. In the flow channels, there exist only several discrete micro bubbles at a low current density (0.04 A/cm 2 ) and a large flow velocity (133 mm/s). At a current density (0.2 A/cm 2 ) and a flow velocity (67 mm/s), a number of gas slugs are formed in the follow channels, in addition to discrete micro bubbles. At a high current density (1 A/cm 2 ) and a flow velocity (67 mm/s), more bubbles appear in the channel, and the flow field is dominated by slug or annular flows. These investigations can help to better understand the two-phase flow and bubble detachment mechanism, and provide a foundation for electrochemical reaction, multiphase flow studies and optimize the design of gas diffusion layers and flow fields for PEMECs in the future.

08 HYDROGEN↗
DOE OSTI2023

High-Throughput Electrochemical Characterization of Aqueous Organic Redox Flow Battery Active Material

The development of redox-active organics for flow batteries providing long discharge duration energy storage requires an accurate understanding of molecular lifetimes. Herein we report the development of a high-throughput setup for the cycling of redox flow batteries. Using common negolyte redox-active aqueous organics, we benchmark capacity fade rates and compare variations in measured cycling behavior of nominally identical volumetrically unbalanced compositionally symmetric cells. We propose figures of merit for consideration when cycling sets of identical cells, and compare three common electrochemical cycling protocols typically used in battery cycling: constant current, constant current followed by constant voltage, and constant voltage. Redox-active organics exhibiting either high or low capacity fade rates are employed in the cell cycling protocol comparison, with results analyzed from over 50 flow cells.

Electrochemistry↗
DOE OSTI2022

A Review: Flow Electrode Capacitive Deionization for Improved Electrochemical Water Desalination

In many places of the world people have continued to suffer from major droughts and water shortages. With climate change climbing in intensity, these dry conditions will only worsen. With much of the world’s water in the ocean, both saltwater and brackish water have been identified as key water sources. Currently, there are several technologies available for water desalination and treatment such as reverse osmosis, capacitive deionization, electrodialysis, and flow electrode capacitive deionization. This paper will briefly review each of these technologies and propose a new design to improve the current flow electrode capacitive deionization architecture. The new design uses a current collector flow-electrode architecture that has the potential to achieve record thermodynamic energy efficiencies. This formulation is proprietary to Lawrence Livermore National Laboratory.

36 MATERIALS SCIENCE↗