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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Microelectrode Arrays for Electrochemical Cycling of Individual Battery Particles

The electrochemical characterization of battery materials is usually performed on porous electrodes containing conductive additives, binders, and ensembles of redox-active particles at densities as high as 10 15 cm –3 . These complex structures often obscure individual battery particles’ intrinsic properties, hindering insights into the fundamentals of battery electrochemistry. To address this challenge, we developed microelectrode arrays to enable the charge and discharge of individual battery particles in liquid electrolytes. In this Methods and Protocols paper, we describe the fabrication of the microelectrode array chips, the assembly of particles onto microelectrodes, and the different types of electrochemical techniques that can be used, including galvanostatic cycling, cyclic voltammetry, potentiostatic intermittent titration, and electrochemical impedance spectroscopy. We use micron-sized lithium cobalt oxide as a model system to showcase the reliability and versatility of single-particle electrochemical experiments enabled by our microelectrode array. In conclusion, we aim to provide a detailed description to promote future uses of microelectrode arrays in fundamental research of batteries and other electrochemical systems.

25 ENERGY STORAGE↗
DOE OSTI2025

Surface Manipulation on Pt 2.2 Ni(111) Nanocatalysts for Boosting Their ORR Performance in Alkaline Media

We have previously shown that Pt–Ni alloy nano-octahedra with {111} facets exhibit outstanding electrochemical performance in the oxygen reduction reaction (ORR) in acidic media when their surfaces are finely tailored at the atomic level. Here, in this investigation, we further refine the surface structure of Pt 2.2 Ni octahedral nanocatalysts to improve ORR performance in a 0.1 M KOH solution using diverse surface manipulation techniques. Through systematic analysis using electrochemical CO stripping, cyclic voltammetry, and X-ray photoelectron spectroscopy, we examined the surfaces of Pt 2.2 Ni octahedral nanocatalysts pretreated with various methods, including etching in acetic acid or perchloric acid, and subsequent electrochemical activation in an alkaline solution or an acidic solution. Among these treatments, those involving acidic media, particularly electrochemical cycling in acidic electrolytes, demonstrated significantly enhanced ORR activity in 0.1 M KOH. The latter exhibited a mass activity of 2.95 A/mg pt and a specific activity of 8.71 mA/cm 2 at 0.90 V, surpassing state-of-the-art Pt/C by 12-fold and 34-fold, respectively. Furthermore, this identified nanocatalyst displayed robust stability, with negligible activity decay observed after 10,000 cycles. This study suggests that the improved ORR activity can be attributed to the Pt-rich surfaces with well-preserved {111} lattices on the surface-modified Pt–Ni nano-octahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Spectroscopic Investigation into P(NDI2OD-T2) Charge Localization

P(NDI2OD-T2), commonly referred to as N2200, stands out as a promising electron-transporting (n-type) polymer for low-cost, flexible (photo)electrochemical applications due to its reversible two-electron reduction and high electron mobility. UV–vis spectroelectrochemistry in the tetrabutyl ammonium hexafluorophosphate/acetonitrile electrolyte shows two sets of chemically reversible redox signals in the cyclic voltammetry corresponding to the reduction of the neutral polymer film to polaronic and bipolaronic species. These electrochemical signatures suggest a distinct electronic reorganization upon reduction (polaron/bipolaron formation), highlighting the need for molecular-level insights into how charges are accommodated within the polymer backbone. While it has been previously hypothesized that charge predominantly localizes on the naphthalene diimide (NDI) unit during reductive charging, specific changes in atomic environments that confirm this localization have not been characterized in n-type polymers. Herein, we use near-edge X-ray absorption fine structure (NEXAFS) spectroscopy to probe electronic transitions in an electrochemically charged polymer to deduce charge localization. The O K-edge (1s) spectra exhibit two distinct π* peaks; the intensity of the lower-energy π* a peak that corresponds to an excitation to a largely localized carbonyl state decreases with reductive potentials relative to the higher-energy π* b peak. We corroborate this with Raman spectroscopy at different potentials, which shows a decrease in intensity on the C–C/C═C and C═O stretching bands of NDI as well as a red shift of the carbonyl band due to the formation of a polaron on the NDI. Additionally, new Raman active NDI signals associated with elongated C═O and C═C bonds are observed at lower energy during the formation of charged states. Together with theoretical calculations, these findings show that the injected charge spatially localizes on the NDI units and is dominantly distributed on the carbonyl groups. In conclusion, the combination of NEXAFS, optical and vibrational spectroscopies, and theoretical calculations is generalizable to other pi-conjugated polymers and can identify charge localization for the further development of organic semiconductors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Synthesis and Characterization of [Ni(H 2 O)(7-P Ph 2 N ArSO3 ) 2 ](NaBF 4 ) for Light-Driven Quantum Dot-Catalyst Hydrogen Evolution

Light-driven hydrogen generation from water is a route to carbon-neutral fuels. However, the integrated light absorbers and catalysts must be compatible and functional under the same conditions. A sulfate-functionalized complex, [Ni(H 2 O)(7-P Ph 2 N ArSO3 ) 2 ](NaBF 4 ), where P Ph 2 N ArSO3 = 4-(3,6-diphenyl-1,3,6-azadiphosphepan-1-yl)benzenesulfonate), was synthesized and characterized. A solid-state structure from single-crystal X-ray crystallography is also reported. The electrocatalytic activity for hydrogen evolution of this complex in 7:3 H 2 O:CH 3 CN was characterized by cyclic voltammetry and controlled potential electrolysis, with a maximum observed rate of 83 s –1 . Density functional theory was used to characterize the favorable binding of the sulfate functionalities to cadmium sulfide quantum dots. Experimental assembly of these catalysts onto cadmium sulfide quantum dots was successful. In conclusion, both fast electron transfer and light-driven pH-dependent hydrogen evolution were observed.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Alizarin Multilayers Adsorbed onto Glassy Carbon Electrodes for Electrochemical Sequestration of Manganese, Sodium, and Lithium Cations

The development of efficient methods for metal ion recovery and water remediation is critical for addressing the nation’s urgent need for secure domestic supply chains, overcoming critical materials challenges, and ensuring resilient manufacturing. Here, we present a novel approach for synthesizing stable Alizarin (Alz, 1,2-dihydroxy anthraquinone) multilayers on glassy carbon electrodes (GCEs) for electrochemical sequestration of manganese, sodium, and lithium cations. Alz-GCEs exhibit negatively shifted reduction potentials, indicating strong interactions between Alz and metal cations through metal-coupled electron transfer (MCET) mechanisms. The cation binding interactions and redox behavior of these electrodes were investigated using cyclic voltammetry (CV) and density functional theory (DFT) calculations. Our results demonstrate that Alz forms multilayer structures on GCEs with redox properties that are modulated by the presence of metal cations in the electrolyte. DFT calculations provide insights into the electrochemical mechanism, indicating both stepwise and concerted pathways for metal binding. The findings highlight the potential of Alz-GCEs for efficient and selective metal ion capture, which could be useful for developing sustainable materials for critical metal recovery and water remediation. This work suggests that redox-mediated organic adlayers are promising candidates for advancing electrochemical separation technologies of metal ions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Cobalt-Doped Tungsten Oxide Nanoparticles for Electrochemical Sensing and Detection of a Penicillin Antibiotic: Amoxicillin

A sensitive electrochemical sensor for the determination of antibacterial amoxicillin (AMXL) in pharmaceutical dosage and environmental samples was developed, since its residues were found in water, food, and biological samples to pose adverse health risks such as immune–allergic reactions and antimicrobial resistance. WO 3 -based sensors are reported to provide higher sensitivity, selectivity, and stability during the electrochemical reaction. Considering this, Co-doped WO 3 nanostructures were synthesized by the hydrothermal method yielding a mixture of nanoparticle and nanorod structures and applied to the assay of AMXL. Extensive characterizations were carried out by SEM, XRD, TEM, and XPS analysis that confirm the monoclinic crystal structure with a uniform Co distribution in the WO 3 lattice. The optimum doping amount of Co in the lattice is found to be 1.80 at %. The electrochemical performance of the Co-WO 3 /carbon paste electrode (CPE) was evaluated for the determination of AMXL under optimum conditions using cyclic voltammetry, electrochemical impedance spectroscopy, and square wave voltammetry. The Co-WO 3 /CPE showed two linear detection ranges at 0.01–0.1 μM with the linear regression I pa = 3.73 [AMXL] + 0.77 with R 2 = 0.96 and at 0.1 to 30.0 μM with the linear regression I pa = 3.76 [AMXL] + 0.69 with R 2 = 0.95. The limit of detection was 9.1 nM (SNR = 3), and the limit of quantification was 30.6 nM (SNR = 10). The sensitivities for lower and higher concentration ranges were 63.22 and 63.73 μA μM –1 cm –2 , respectively. Furthermore, Co-WO 3 /CPE showed high selectivity and anti-interference capabilities. In conclusion, the sensing and disposable Co-WO 3 /CPE sensor showed a great potential for AMXL analysis in spiked soil, water, and Amoxil tablet samples with desirable percentage recovery.

Shanbhag, Mahesh M. [KLE Technological University,↗
DOE OSTI2025

Bis( tert -butoxydiphenylsilyl)amide Divalent Lanthanide Complexes

The development of new ligand systems to stabilize “nontraditional/ non-classical” divalent lanthanides is key to tuning the chemical and physical properties of their mixed principal quantum number 4f n 5d 1 ground states. The design and study of novel ligand systems which stabilize occupation of differing orbitals within the 5d manifold for these ions constitutes an area ripe for exploration. Our efforts toward the development of redox-innocent bulky silylamide ligands to stabilize pseudo-octahedral coordination geometries for divalent lanthanides have resulted in the synthesis of the bis( tert -butoxydiphenylsilyl) amide ligand, whose coordination complexes with Sm 2+ , Eu 2+ , and Yb 2+ are reported herein. These systems have been fully characterized by single-crystal X-ray diffraction, elemental analysis, cyclic voltammetry, direct-current magnetometry, and infrared, nuclear magnetic resonance, and electronic absorption spectroscopies. Attempts to extend this system to the more reducing Tm 2+ ion resulted in an inseparable mixture of products from which crystals of the analogous Tm 2+ species and a reduced dinitrogen, bimetallic Tm 3+ -Tm 3+ complex bridged by a η 2 -N 2 3− radical could be identified. Though progress toward six-coordinate complexes of reducing “traditional/ classical” divalent ions is noted for these systems, further work is needed to improve the synthetic utility of this ligand framework for the study of “non-traditional/non-classical” divalent lanthanides with a mixed-principal quantum number 4f n 5d 1 ground state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Ligand-Driven Electrochemical Tuning of Co 6 Se 8 Chevrel Clusters

Molecular “Chevrel-type” clusters of the formula Co 6 Se 8 L 6 (L = neutral ligand) are a well-studied class of clusters due to their utility as molecular analogues to the Chevrel extended solid phase and their application as subunits in hierarchical materials. However, their solution and optical properties remain relatively underexplored. Aiming to develop the fundamental relationships between the molecular and electronic structures of these clusters and their electrochemical and photophysical properties, this work reports the preparation of a series of Co 6 Se 8 (P­(C 6 H 4 R) 3 ) 6 -type clusters with R = Cl (1), F (2), H (3), CH 3 (4), and OCH 3 (5) via a stepwise synthetic approach. Solution and solid-state experimental characterization and density functional theory calculations reveal that the Co 6 Se 8 cores of 1–5 maintain consistent electronic and structural properties despite the variation of the triarylphosphine ligand para-substituent Hammett parameters (σ p ). However, cyclic voltammetry measurements indicate that the electron transfer energetics of 1–5 are strongly influenced by ligand substitution, with the E 1/2 of a given redox event spanning ∼0.5 V depending on the triarylphosphine ligand’s σ p . In conclusion, these findings support the characterization of Co 6 Se 8 clusters as atomically precise nanoclusters with both the structural robustness and the electrochemical tunability needed to act as components in larger charge transfer assemblies.

Wheaton, Amelia M. [Argonne National Laboratory (A↗
DOE OSTI2025

Electrocatalytic Ammonia Oxidation with Coordinatively Saturated Ruthenium Catalyst

This communication describes the investigation of a coordinatively saturated complex [Ru(tpy)(dmabpy)Cl] + ([Ru(Cl)] + ) as an ammonia oxidation catalyst. Cyclic voltammetry measurements show an ideal S-shaped wave, indicating total catalysis conditions with a k obs (TOF max ) of 9360 h −1 . The reaction was found to be first-order in [Ru(Cl)] + and third-order in [NH 3 ]. Stoichiometric reactions of the one-electron oxidized species, [Ru(Cl)] 2+ , were monitored following the addition of 15 NH 3 using 1 H and 15 N NMR spectroscopy. These experiments showed that the chloride-coordinated complex rapidly converts NH 3 to N 2 . NMR spectroscopy and electrochemistry results definitively show that NH 3 does not substitute the Cl − ligand to form the previously reported [Ru(NH 3 )] 2+ catalyst which operates by a different mechanistic pathway. Taken together these results indicate outersphere electron transfer mediated ammonia oxidation reaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Homoleptic An(IV) Dimethyl Sulfoxide Complexes of Th–Pu Enable Insight into Solution Speciation and Redox

A family of 8- and 9- coordinate homoleptic dimethyl sulfoxide An(IV) complexes is used to evaluate the solvation properties of tetravalent actinide ions in dimethyl sulfoxide (DMSO) vs aqueous media. These compounds are prepared from aqueous mixtures of DMSO and yield crystalline solids, whose solid-state electronic absorption spectra are compared to solution phase spectra, providing insight into the solution speciation. The thermodynamics of the equilibria between the 8- and 9-coordinate compounds were determined experimentally and computationally, showing a trend that correlates with ionic radius. Cyclic voltammetry data for the +IV/+III couples of Np and Pu in the DMSO electrolyte indicate that the +IV ions are significantly stabilized compared to aqueous media due to the more donating nature of DMSO compared to water. As a result, computational studies of these systems indicate that further reactivity may take place upon reduction to the +III oxidation state.

Actinides↗
DOE OSTI2026

A Guide to Nonaqueous Electrochemistry of f-Element Complexes

Electrochemistry is a powerful tool for assessing and understanding the redox chemistry of molecular complexes. Cyclic voltammetry enables the f-element community to study molecules in unusually high or low oxidation states, which potentially pose important broad-scope questions of electronic structure. In the pursuit of boundary-pushing compounds, reactive air- and moisture-sensitive species are often encountered, which can be challenging to characterize, especially when they are chemically incompatible with certain solvents, electrolytes, or electrodes or when their potentials lie outside of common electrochemical windows. Nonaqueous solvents and pseudo reference electrodes complicate many of the standard practices in acquiring high-quality and reproducible electrochemical data. This guide presents a detailed discussion of selecting appropriate cell conditions and referencing and addresses metrics for evaluating electrochemical and chemical reversibility. These methodological approaches have been extended to best practices for the electrochemical analysis of radioactive transuranic complexes.

Electrodes↗
DOE OSTI2026

Coordination-Induced Weakening of N–H Bonds Driven by Bimetallic Cooperativity in Zr/Co Compounds

The bond dissociation free energy (BDFE) of the element-hydrogen bonds of protic substrates have been found to decrease upon metal coordination. Herein, an early/late heterobimetallic complex is used to examine the impact on the BDFE N−H when the substrate binding site and the redox-active site are two different metals that are spatially separated. A tris- (phosphinoamide) framework is used to link a d 0 ZrIV center with an accessible substrate binding site to a coordinatively saturated redox-active Co center, which serves as an appended electron reservoir. A series of aniline, amido, and imido Zr/Co model compounds were synthesized starting from the Zr IV /Co −I aniline adduct PhH 2 N−Zr(MesNP i Pr 2 ) 3 CoCN t Bu (2). 2,4,6-tristert- butylphenoxyl radical ( t Bu 3 ArO • ) was used to abstract one or two H atoms and produce the amido and imido complexes PhHNZr( MesNP i Pr 2 ) 3 CoCN t Bu (3) and PhN≡Zr(MesNP i Pr 2 ) 3 CoCNtBu (4), respectively. Using open-circuit potential measurements, the BDFE N−H within 2 and 3 were determined to be 37 kcal/mol (2) and 55 kcal/mol (3). Cyclic voltammetry measurements were conducted to determine the Co I/0 and Co 0/−I redox potentials. The pK a s were then estimated using the Bordwell equation to provide further insight into the thermochemical aspects of the observed proton coupled electron transfer (PCET) reactions.

Bond dissociation free energy↗
DOE OSTI2026

Synthesis and Reactivity of Heteroleptic U 4+ Alkyl, Benzyl, and Hydride Imidophosphorane Complexes

A series of heteroleptic U 4+ benzyl, neopentyl, and methyl complexes supported by the imidophosphorane ligand, [N = P(N,N′-ditert-butylethylenediamide)(diethylamide)] 1− (NP*), were synthesized from the monoiodide precursor, [UI(NP*) 3 ]. These heteroleptic complexes were synthesized through the selective formation of [UI(NP*) 3 ] under transmetalation conditions in the reaction between [UI 4 (1,4-dioxane) 2 ] and K[NP*]. Formation of the homoleptic complex [U(NP*) 4 ] was not observed even in the presence of excess K[NP*]. The oxidation and hydrogenolysis reactivity of the neopentyl complex, [U(Npt)- (NP*) 3 ] (Npt = neopentyl) was explored. While cyclic voltammetry indicates a potentially isolable U5+ alkyl cation, chemical oxidation of the neopentyl complex results in the isolation of a cationic U 4+ complex with a bound diethyl ether in the primary coordination sphere, [U4+(NP*)) 3 (Et 2 O)][(BArF 24 )] (BArF 24 = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate). Notably, hydrogenolysis of [U(Npt)(NP*) 3 ] with H2 gas at −20 °C results in the formation of a terminal hydride intermediate confirmed by in situ NMR spectroscopy and deuterium labeling with D 2 . The connectivity and structural parameters of this hydride intermediate, [UH(NP*) 3 ], which rapidly thermally decomposes to the homoleptic complex, [U(NP*) 4 ], can be confirmed by single-crystal X-ray diffraction studies of a crystal grown by chilling the reaction mixture. The identity of [U(NP*) 4 ] was confirmed by its direct, bulk synthesis from [U(Me)(NP*) 3 ] and HNP* in a protonolysis reaction.

Alkyls↗
DOE OSTI2024

Oxidation Temperature-Dependent Electrochemical Doping of WO 3 Deposited via Atomic Layer Deposition

Silicon-based photoelectrochemical devices show promise for the performance of light-driven CO 2 reduction but suffer from instability under photoelectrochemical conditions relevant to CO 2 reduction. Coating silicon electrodes with thin layers of metal oxides has shown promise to passivate unstable silicon surfaces, and many different metal oxides can be deposited on silicon using various techniques. In this study, we investigate the fundamental photoelectrochemical performance of WO 3 -coated silicon photoelectrodes, which were generated by oxidation of W-metal films deposited via atomic layer deposition on both degenerately doped (nSi + ) and low-doped (pSi) silicon. Two different oxidation temperatures were investigated (400 and 600 °C), and it was found that the monoclinic phase of WO 3 predominates at both temperatures but that more grain boundaries are present in the 600 °C film. From X-ray photoelectron spectroscopy, the stoichiometry of both films was found to be 1:3 W:O, and low electron energy loss experiments indicate band gaps of 3.0 and 3.1 eV for 400 and 600 °C films, respectively. Cyclic voltammetry experiments showed that the electron transfer kinetics increased after continued redox cycling, particularly for the material produced at 400 °C. X-ray photoelectron spectra suggest that the observed increase in electrode conductivity is due to the formation of oxygen vacancies in the film. Electrochemical impedance spectroscopy indicated that charge transport through the films was impacted by the grain boundaries that formed during oxidation of the film. Photoelectrochemical studies on pSi/WO 3 electrodes were highly variable, only producing a photocurrent and photovoltage with some samples. Our best sample, formed at 400 °C, produced a photovoltage of 180 mV, which is lower than what has previously been reported for WO 3 -coated silicon (500 mV). We hypothesize that the variability in photoelectrochemical experiments arose from a roughened WSiO x interface that is generated during film preparation. WO 3 shows promise as a metal oxide coating for silicon, but our results suggest that formation of a high-quality interface between Si and WO 3 is vital for best performance.

Charge transfer↗
DOE OSTI2024

Diazonium-Functionalized Silicon Hybrid Photoelectrodes: Film Thickness and Composition Effects on Photoelectrochemical Behavior

Aryl diazonium electrografting is a powerful method for imparting molecular functionality onto various substrates by forming a stable carbon-surface covalent bond. While the high reactivity of the aryl radical intermediate makes this method fast and reliable, it can also lead to the formation of an insulating and disordered multilayer film. These thick films affect electrochemical performance, especially for semiconductor substrates used in photoelectrochemical applications. For this work we studied the effects of film thickness and composition by electrografting in situ-generated aminobenzene diazonium salts onto both n-type and p-type silicon electrodes at fixed potentials. Next, we attached ferrocene to the amine-terminated films and probed their (photo)­electrochemical behavior. Cyclic voltammetry measurements showed decreased electrochemical reversibility with increasing diazonium film thickness; this reversibility was restored when ferrocene was incorporated throughout the film with a layer-by-layer deposition process. Finally, we compared the behavior of dark p-type electrodes to n-type photoelectrodes and observed differences in the electrochemical reversibility that we attribute to the change in potential drop across the two interfaces.

charge transfer↗
DOE OSTI2026

Rhodium-Catalyzed Arene Alkenylation Using Benzoquinone Derivatives as Oxidants

The Rh-catalyzed conversion of olefins and arenes to alkenyl arenes using [(η 2 -C 2 H 4 ) 2 Rh(μ-OPiv)] 2 as the catalyst precursor and 12 ortho- and para-substituted benzoquinone derivatives as the in situ oxidant is reported. Included are comparative studies of the quinone derivatives for (1) rate of styrene production from benzene and ethylene, (2) Markovnikov to anti-Markovnikov selectivity for reactions of benzene and propylene, and (3) ortho/meta/para selectivity when using tert-butylbenzene as the arene. Cyclic voltammetry was utilized to measure reduction potentials for each quinone to determine any possible influence of the quinone redox potential on arene alkenylation rate and selectivity. While significant differences in selectivity are observed between ortho -quinone derivatives, such differences are minimal when para-substituted quinones are utilized. These results suggest that ortho -benzoquinone derivatives likely serve as bidentate ligands, which explains the stronger influence on catalyst activity of ortho -benzoquinone identity compared to para -benzoquinones. Although ortho -benzoquinones generally give styrene production rates faster than those of para -benzoquinones, 3,5-di- tert -butyl- ortho -benzoquinone and ortho -chloranil react with ethylene to form bicyclo[2.2.2]oct-5-ene-2,3-dione derivatives as a significant side product.

aromatic compounds↗
DOE OSTI2024

Electrochemical and Chemical Reactivities of Titanium Oxide-Based Materials with a Chloroaluminate Ionic Liquid Electrolyte for Aluminum Batteries

Here, by selecting three different types of electrode materials, we intended to better understand the Al 3+ intercalation chemistry of titanium oxide-based frameworks with an acidic chloroaluminate electrolyte. In agreement with previous reports, we confirmed that the native interstitial sites of anatase TiO 2 are less prone to accommodate Al 3 + than Li + or Na + ions, while introducing cationic vacancies largely increases the electrochemical storage capacity. Upon the first cycle, the highest reversible capacity, up to 277 mAh/g, was obtained for a hydrated layered structure featuring cationic vacancies. Total scattering data showed that the insertion of Al 3+ ions induced a strong distortion of the framework. In addition, combined 27 Al MAS NMR and DFT calculations revealed that in oxy-hydroxylated vacant sites, the coordination mode of Al 3+ ions depends on the arrangement of anions around vacancies inducing the occurrence of 4-, 5-, and 6-fold coordination modes. Further cycling experiments revealed a progressive capacity fading for all electrode materials. Using cyclic voltammetry on the used electrolyte, we evidenced that a partial dissolution has occurred, which is more pronounced for the layered hydrate compound, and that solubilized species are electrochemically active, giving rise to specific signatures in both CVs and galvanostatic experiments. Raman spectroscopy enabled us to characterize these species, which are derived from the Ti-Cl system. The solubilized species, however, eventually precipitated, as shown by a purple deposit observed on the separator and tentatively assigned to TiCl 3 , known to be insoluble in this medium. By providing further information on the Al 3+ intercalation chemistry and a better understanding of the electrochemical and chemical reactivities of electrode materials, this work will enable progress to be made in the development of aluminum-ion batteries.

Al3+-ion insertion chemistry↗
DOE OSTI2024

Impact of Synthetic Parameters on Structure and Electrochemistry of High-Entropy Layered Oxide LiNi 0.2 Co 0.2 Mn 0.2 Al 0.2 Fe 0.2 O 2

Here, this study explored a high-entropy layered oxide (HELO), LiNi 0.2 Co 0.2 Mn 0.2 Al 0.2 Fe 0.2 O 2 , prepared by coprecipitation followed by heat treatment. Coprecipitation yielded a kinetically favored product, and the subsequent heat treatment under various temperatures and times allowed tuning the material toward more thermodynamically favored structures. Refinement of X-ray powder diffraction (XRD) revealed that after 450 °C treatment, ~12% of the Ni 2+ in the structure was located within the lithium cation layer. After heat treatment at 600, 700, and 800 °C, there was a continued decrease of Ni 2+ in the lithium cation layer to 9.3, 6.3, and 3.7%, respectively. Longer heat treatment times at 800 °C decreased the level to 2.5%. Electrochemical behavior was evaluated by cyclic voltammetry, galvanostatic cycling, rate capability testing, and electrochemical impedance spectroscopy, where increased loaded voltage, functional capacity, rate capability, and decreased impedance were observed for samples treated at higher temperatures with lower cation mixing. X-ray absorption near edge spectroscopy (XANES) data indicated that the redox activity of Ni and Co was dominant in the electrochemistry, while the participation of Mn or Fe was minimal. The level of Ni oxidation state change between charge and discharge related to the heat treatment temperature where the samples with high cation mixing showed lower capacity consistent with some Ni 3+ in the transition metal layer inaccessible for electron transfer. Longer heat treatment times at 800 °C did not continue to provide a benefit in electrochemical function even with some additional reduction in cation mixing.

25 ENERGY STORAGE↗