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Results for “electrolyte reactions”

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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Stability Enhancement in Na 0.67 Fe 0.2 Mn 0.8 O 2 Positive Electrodes via Spherical Coprecipitated Hydroxide Precursor Synthesis for Na-Ion Batteries

Mn/Fe-based layered transition metal oxides (LTMOs) are promising positive electrode materials for sodium-ion batteries (SIBs) due to their high abundance, low cost, and stable price fluctuations. At commercial scale, the fabrication of these materials commonly employs coprecipitation of hydroxide precursors, which allows for the scalable synthesis of uniform, dense particles with a tunable morphology. However, the common chelating agent (ammonia) forms unstable complexes with Fe 2+ ions, resulting in uncontrollable particle morphology and poor electrochemical properties. Here, in this study, three chelation strategies (no chelation, ammonia, oxalate) for Fe/Mn-based hydroxides are evaluated. It was found that oxalate chelation produced uniform, dense spherical hydroxide particles while particles via ammonia / no chelate routes exhibited no morphological control. The LTMOs synthesized from the oxalate-chelated hydroxide precursor formed uniform spherical particles, while the other two LTMOs showed greater variation in particle morphology. The oxalate-chelated LTMO electrode exhibited increased cycling stability due to reduced parasitic reactions with the electrolyte, as characterized by static leakage current measurements and electrochemical impedance spectroscopy.

25 ENERGY STORAGE↗
DOE OSTI2020

Highly reversible oxygen redox in layered compounds enabled by surface polyanions

Oxygen-anion redox in lithium-rich layered oxides can boost the capacity of lithium-ion battery cathodes. However, the over-oxidation of oxygen at highly charged states aggravates irreversible structure changes and deteriorates cycle performance. Here, we investigate the mechanism of surface degradation caused by oxygen oxidation and the kinetics of surface reconstruction. Considering Li 2 MnO 3 , we show through density functional theory calculations that a high energy orbital (lO 2p’ ) at under-coordinated surface oxygen prefers over-oxidation over bulk oxygen, and that surface oxygen release is then kinetically favored during charging. We use a simple strategy of turning under-coordinated surface oxygen into polyanionic (SO 4 ) 2- , and show that these groups stabilize the surface of Li 2 MnO 3 by depressing gas release and side reactions with the electrolyte. Experimental validation on Li 1.2 Ni 0.2 Mn 0.6 O 2 shows that sulfur deposition enhances stability of the cathode with 99.0% capacity remaining (194 mA h g -1 ) after 100 cycles at 1 C. Our work reveals a promising surface treatment to address the instability of highly charged layered cathode materials.

25 ENERGY STORAGE↗
DOE OSTI2025

Thermal processing to modulate surface chemistry and bulk charge distribution in nickel-rich layered lithium positive electrodes

The broader application of nickel-rich layered oxides as positive electrode materials for lithium-ion batteries has been hindered by their high manufacturing cost and inferior cycling stability. Thermal processing, which is integral to electrode materials manufacturing and fundamental in materials science, has not been fully utilized to design advanced positive electrode materials. Herein, we demonstrate the capability of using quenching heat treatment to regulate Li distribution and modulate electronic structure near particle surface. The resulting materials exhibit less parasitic reactions with the electrolyte and an improved charge distribution homogeneity in secondary particles, leading to more stable cycling performance at high voltages (4.5 V vs Li/Li + ). Our synchrotron X-ray analyses reveal the underlying interplay between surface structure and bulk charge distribution in positive electrode materials particles. While strategies used to stabilize positive electrode materials through compositional control, surface modification, and electrolyte engineering have become mature, thermal processing can be advantageous to further improve positive electrode materials manufacturing.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Ni/NiO Reference Electrode Potential Measurements in Molten CaCl 2 –CaO

A direct oxide reduction (DOR) process is used to reduce PuO 2 to Pu metal via Ca metal. Molten CaCl 2 is commonly used as the electrolyte for this reaction. As the DOR reaction proceeds, CaO accumulates in the salt and must be measured in real-time to know when the reaction has gone to completion. Open circuit potential (OCP) was measured in this report between a reference electrode consisting of Ni/NiO contained in a MgO tube and a tungsten working electrode. Two methods of CaO additions were performed over several experiments, and both methods correlated to a 0.11 to 0.23 V decrease in OCP up to 14.4 wt% CaO. CaO concentrations were separately measured via sampling and acid-base titration. A plot of OCP versus concentration of CaO fits the Nernst equation with the CaO powder additions up to 5.2 wt% and also at the higher end of the CaO pellet concentration range. While the MgO tubes were observed to be structurally stable in the molten salt, scanning electron microscopy and energy dispersive X-ray spectroscopy showed that Mg in the tubes had been partially replaced with Ca.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Influence of Single-Crystalline Morphology on the Electrochemical Behavior of High-Nickel Layered Oxide Cathodes

High-Nickel layered oxides are being pursued for their high specific capacities. With increasing nickel content, the layered oxides also suffer from structural and morphological instabilities, which degrade the electrochemical performance. Single-crystalline morphology presents an attractive solution to these problems, simultaneously reducing surface area available for parasitic reactions and preventing electrolyte penetration into the bulk with the removal of grain boundaries. Single-crystal cathodes have already shown promising results with NMC composition cathodes, but there are still gaps in the fundamental understanding of how single-crystalline morphology alters electrochemical behavior. We attempt to fill some of these gaps by studying in detail the electrochemical operation of polycrystalline and single-crystalline LiNiO 2 (LNO). Single-crystal LNO is prepared through a molten salt method yielding high-quality, distinct crystals with comparable lattice chemistry to polycrystalline LNO. The single-crystal LNO achieves far greater stability during long-term cycling, reaching 500 cycles with 82.5% capacity retention. Interestingly, the single-crystalline LNO also displays superior rate performance, delivering 157 mA h g −1 at 10C discharge rate. Investigation of the phase evolution behavior during cycling strongly suggests that the absence of grain boundaries in single-crystalline LNO is responsible for the superior performance.

25 ENERGY STORAGE↗
NASA NTRS1979

Electrochemical fluorination of trichloroethylene and N, N-dimethyltrifluoroacetamide

Fluorination of trichloroethylene and N, N-dimethyltrifluoroacetamide was carried out on a laboratory scale in an advanced Simons type electrochemical apparatus which could be operated automatically from ambient to 50 psi pressure. A variety of fluorine-substituted products are formed, depending upon electrolysis conditions and concentrations of reactant relative to the NaF, KF, HF electrolyte. A new reaction mechanism of electrochemical fluorination of trichloroethylene is proposed. The solvency-to-fluorine content relationship of fluorinated N, N-dimethyltrifluoroacetamide is described.

Hsu, L. C.↗
NASA NTRS1979

Electrochemical fluorination of trichloroethylene and N, N-dimethyltrifluoroacetamide

The paper presents the results of experiments concerning the fluorination of trichloroethylene and N, N-dimethyltrifluoroacetamide carried out on a laboratory scale in an advanced 'Simons' type electrochemical apparatus which could be operated automatically from ambient to 50 psi pressure. It is shown that a variety of fluorine-substituted products are formed, depending upon electrolysis conditions and concentrations of reactant relative to the NaF, KF, HF electrolyte. A new reaction mechanism of electrochemical fluorination of trichloroethylene is proposed. Finally, the solvency-to-fluorine content relationship of fluorinated N, N-dimethyltrifluoroacetamide is described.

Hsu, L.-C.↗
DOE OSTI2026

Identification of Solid-Electrolyte Interphase Species by Joint Characterization of Li-Ion Battery Chemistry by Mass Spectrometry and Electrochemical Reaction Networks

The formation and stability of the solid-electrolyte interphase (SEI) play central roles in determining the long-term performance and safety of modern electrochemical energy storage systems. Despite decades of research, the SEI’s heterogeneous, dynamic, and multiphase nature has defied comprehensive molecular-level characterization, creating a critical knowledge gap that limits rational battery design. In this work, we introduce a computational−experimental framework that integrates high-throughput quantum chemistry calculations, data-driven electrochemical reaction networks (eCRNs), stochastic algorithms, and laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry (LDI-FTICR-MS) to unravel SEI formation in carbonatebased electrolytes without imposing predefined mechanisms. We constructed the most comprehensive eCRN to date, spanning over 10,000 species and 209 million reactions. Through stochastic network analysis, we successfully recovered 27 species that were previously reported in the literature and predicted 28 novel SEI species nearly doubling our scientific knowledge in this area. Each new species was rigorously confirmed through advanced mass spectral analysis of its distinct molecular and isotopic signatures. We kinetically refined the formation pathways for a select set of both previously reported and novel SEI products, revealing kinetically feasible elementary reaction mechanisms with activation barriers below 1 eV. This computational−experimental approach deepens our molecular-level understanding of SEI chemistry by resolving which species form and through which decomposition mechanisms they emerge. Such knowledge provides the foundation necessary to connect electrolyte composition to the resulting SEI components, a critical step toward a more informed electrolyte development in next-generation lithium-based batteries.

25 ENERGY STORAGE↗
DOE OSTI2024

Continuous Flow Photoelectrochemical Reactor with Gas Permeable Photocathode: Enhanced Photocurrent and Partial Current Density for CO 2 Reduction

Photoelectrochemical (PEC) CO 2 reduction using a photocathode is an attractive method for making valuable chemical products due to its simplicity and lower overpotential requirements. However, previous PEC processes have often been diffusion-limited leading to low production rates of the CO 2 reduction reaction, due to inefficient gas diffusion through the liquid electrolyte to the catalyst surface, particularly at high current densities. In this study, a gas-permeable photocathode in a continuous flow PEC reactor is incorporated, which facilitates the direct supply of CO 2 gas to the photocathode-electrolyte interface, unlike dark reaction-based flow reactors. This concept is demonstrated using Ag-TiO 2 on carbon paper, illuminated through a quartz window and flowing liquid electrolyte. CO 2 supply is managed via pressure and flow control on the non-illuminated side of the carbon paper. The photocurrent density is significantly influenced by the flow rates and pressure of CO 2 gas, and the electrolyte flow rates. Compared to the traditional H-cell, the continuous PEC flow reactor achieves ≈10-fold increase in CO faradaic efficiency, 30-fold increase in production rate and 16-fold increase in stability without catalyst modifications. This work provides essential insights into the design and application of continuous gas-liquid flow PEC reactor systems, highlighting their potential for other PEC reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Exploring non-adiabaticity to CO reduction reaction through ab initio molecular dynamics simulation

Non-adiabatic chemical reaction refers to the electronic excitation during reactions. This effect cannot be modeled by the ground-state Born-Oppenheimer molecular dynamics (BO-MD), where the electronic structure is at the ground state for every step of ions' movement. Although the non-adiabatic effect has been explored extensively in gas phase reactions, its role in electrochemical reactions, such as water splitting and CO 2 reduction, in electrolyte has been rarely explored. On the other hand, electrochemical reactions usually involve electron transport; thus, a non-adiabatic process can naturally play a significant role. In this work, using one-step CO 2 reduction as an example, we investigated the role of the non-adiabatic effect in the reaction. The reaction barriers were computed by adiabatic BO-MD and non-adiabatic real-time time dependent density functional theory (rt-TDDFT). We found that by including the non-adiabatic effect, rt-TDDFT could increase the reaction barrier up to 6% compared to the BO-MD calculated barrier when the solvent model is used to represent water. Simulations were carried out using explicit water molecules around the reaction site under different overpotentials, and similar non-adiabatic effects were found.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Isothermal Microcalorimetry Analysis of Li/ β -MnO 2 Discharge

Despite widespread use over several decades, the lithium/manganese dioxide (Li/MnO 2 ) discharge mechanism is not completely understood owing to the structural complexity of the material. However, an improved understanding could lead to broader adoption as a primary and even secondary cathode material. Here, we examine the discharge of single-phaseβ-MnO 2 using isothermal microcalorimetry for the first time. Equilibrium voltage and entropy changes are characterized over the entire discharge range and used to rationalize the results. These measurements are supplemented by electrochemical impedance and X-ray diffraction data that give the clearest picture of theβ-MnO 2 lithiation process to date. We find that the first half of discharge is dominated by a two-phase reaction to form Li 0.5 MnO 2 followed by single-phase insertion to a composition of Li 1.0 MnO 2 , which confirms prior first-principles calculations. The tetragonalβ-MnO 2 lattice undergoes asymmetric expansion from Jahn-Teller distorted Mn 3+ to form an orthorhombic LiMnO 2 phase which retains the 1 × 1 tunnel structure. Microcalorimetry results suggest the presence of parasitic reactions occurring during the second half of discharge, which could arise from decomposition of electrolyte or release and reaction of residual water retained in the structure.

Electrochemistry↗
DOE OSTI2023

The nature and suppression strategies of interfacial reactions in all-solid-state batteries

Solid-state Li batteries are promising energy storage devices owing to their high safety and high theoretical energy density. However, the serious interfacial reaction between solid state electrolytes and cathodes deteriorates the battery performance, impeding the realization of long-term cyclability. The buried nature of the interphase layer presents a significant challenge in achieving a comprehensive understanding of the underlying interfacial reaction mechanisms. Herein, we systematically explore the interfacial reaction evolutions and interphase compositions and electronic properties between the popular oxide cathodes and sulfide solid electrolytes (SSEs). This includes analysis of the chemical and electrochemical reactions between cathodes/coatings and SSEs, as well as the electrochemical self-decomposition of SSEs by thermodynamic phase equilibrium analysis. Herein, we disclose that the driving force of the electrochemical reaction at the chemical potential of μ Li is much stronger than that of the chemical reaction, which dominates the interfacial reaction. Preventing the formation of an electronically conductive interphase is crucial in inhibiting the continuous interfacial degradation during long-term cycling, which can be achieved through the optimized combination of cathodes and SSEs, as well as the introduction of functional coatings between them. Based on these findings, the percentage of molar fraction ( f ) of electronically conductive species in the formed interphase is proposed as a key factor for indicating the interfacial stability for the first time. Furthermore, we propose a specific high-throughput screening scheme to filter the functional coating materials by comprehensively evaluating their functionality. The tiered screening identifies 48 coating materials with optimal properties. The work highlights the significant roles of rational coupling of the cathodes and SSEs, and optimizing interfacial coating materials for solid-state batteries. It opens new avenues for engineering an interphase with improved interfacial compatibility to realize long-term cyclability.

25 ENERGY STORAGE↗
DOE OSTI2025

Effect of Electrolyte Ions on Iridium Oxide-Based Water Oxidation Catalysis

The oxygen evolution reaction often limits the efficiency of renewable fuel syntheses due to its sluggish reaction kinetics. Of the factors that have been studied to improve this important reaction is how the choice of the electrolyte may alter the reaction kinetics. Despite its importance, sys-tematic studies of this effect have been relatively rare. Herein, we report an effort toward correcting this deficiency by investigating the effect of nitrate on water oxidation catalyzed by IrO x . The results show that nitrate can suppress the reaction, resulting in a decrease of the rate and an increase in the Tafel slope. The effect was found to be consistent with a microkinetic model incorporating competitive adsorption between reac-tion intermediates and nitrate, suggesting that the reaction mechanism was unaffected by anion identity. Moreover, this blocking effect exhibited dependence on the cations, following a trend Li + ≈ Na + ≈ K + > Cs + > TEA + . The results are expected to find broad applications in electrocatalysis.

Tafel slope analysis↗
DOE OSTI2025

Optimizing semi-hydrogenation of unsaturated hydrocarbons by electrolyte engineering approach

Electrochemical hydrogenation of unsaturated hydrocarbons, when powered by renewables, represents a unique opportunity to substitute current energy-intensive synthetic routes. Modulation of adsorption energies of the organic substrate and key intermediates of the reaction is critical for fine tuning of the yield, selectivity and kinetics of the reaction. Interestingly, mounting evidence exists regarding the role of electrolyte composition in the outcome of semi-hydrogenation reactions. Nevertheless, electrolyte optimization is a complex task, owing to its hybrid nature. Indeed, it is composed of water serving as a proton source, an organic solvent necessary to dissolve the organic substrate and a conducting salt. Herein, we demonstrate that varying conducting salt and organic solvent has a dramatic impact on the outcomes of semi-hydrogenation of alkynes. By varying salt and water concentrations, we demonstrate that water does not serve as a proton source, and instead addition of an acid is necessary. While increasing the acid concentration increases the yield of the reaction, at too large concentrations the hydrogen evolution reaction becomes predominant. Furthermore, by combining electrochemical measurements with spectroscopic techniques including Fourier transform infrared (FTIR) spectroscopy and small angle X-ray spectroscopy (SAXS), we demonstrate that the electrolyte solvation structure dramatically impacts the yield of the reaction. Organic solvents weakly interacting with water, including acetonitrile, form aqueous nanoheterogeneities that prevent the organic substrate from accessing the catalyst interface and thus lead to limited yields. Instead, solvents such as dimethylformamide form homogeneous mixtures with which all reactants can access the interface, leading to yields greater than 80% for optimized compositions.

Zhang, Rongyu↗
DOE OSTI2020

Optical Excitation of a Nanoparticle Cu/p-NiO Photocathode Improves Reaction Selectivity for CO 2 Reduction in Aqueous Electrolytes

We report the light-induced modification of catalytic selectivity for photoelectrochemical CO 2 reduction in aqueous media using copper (Cu) nanoparticles dispersed onto p-type nickel oxide (p-NiO) photocathodes. Optical excitation of Cu nanoparticles generates hot electrons available for driving CO 2 reduction on the Cu surface, while charge separation is accomplished by hot-hole injection from the Cu nanoparticles into the underlying p-NiO support. Photoelectrochemical studies demonstrate that optical excitation of plasmonic Cu/p-NiO photocathodes imparts increased selectivity for CO 2 reduction over hydrogen evolution in aqueous electrolytes. Specifically, we observed that plasmon-driven CO 2 reduction increased the production of carbon monoxide and formate, while simultaneously reducing the evolution of hydrogen. Our results demonstrate an optical route toward steering the selectivity of artificial photosynthetic systems with plasmon-driven photocathodes for photoelectrochemical CO 2 reduction in aqueous media.

25 ENERGY STORAGE↗