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At least 433 records · Page 24

All sources NASA NTRS DOE OSTI

DOE OSTI2026

An Acid-Free, Temperature-Based Cation Contamination Removal Strategy for PEM Water Electrolysis

It is widely understood that the durability and reliability of polymer electrolyte membrane (PEM) water electrolyzers are heavily dependent on feedwater purity, with cation contaminants that originate from incomplete water purification and balance of plant materials significantly harming electrolyzer performance. However, contamination remains a challenge and a common cause of failure at the stack level, indicating the need for strategies to recover the performance of contaminated cells. In this study, we investigate the effects of temperature on the uptake, electrochemical impacts, and removal of contaminant calcium and iron cations. Lower operating temperatures increase the sensitivity of the cell performance to contaminant cations, while also decreasing cation uptake and promoting contaminant removal. Computational charge transfer modelling shows that lower temperature increases the concentration of contaminant at the cathode and facilitates their removal from the cell. By testing single cells under scenarios designed to mimic stack temperature dynamics, we investigate low-temperature operation as an approach to stack-relevant contaminant recovery. Together, these results demonstrate that the low-temperature recovery approach is a promising approach for acid-free contamination recovery for PEM water electrolysis to promote stack reliability and durability.

08 HYDROGEN↗

DOE OSTI2016

Effect of Organic Cations on Hydrogen Oxidation Reaction of Carbon Supported Platinum

Effect of organic cations on hydrogen oxidation reaction (HOR) of carbon supported platinum (Pt/C) is investigated using three 0.1 M alkaline electrolytes, tetramethylammonium hydroxide (TMAOH), tetrabutylammonium hydroxide (TBAOH) and tetrabutylphosphonium hydroxide (TBPOH). Rotating disk electrode experiments indicate that the HOR of Pt/C is adversely impacted by time-dependent and potential-driven chemisorption of organic cations. In-situ infrared reflection adsorption spectroscopy experiments indicated that the specific chemisorption of organic cations drives the hydroxide co-adsorption on Pt surface. The co-adsorption of TMA + and hydroxide at 0.1 V vs. reversible hydrogen electrode is the strongest; consequently, complete removal of the co-adsorbed layer from Pt surface is difficult even after exposure the Pt surface to 1.2 V. Conversely, the chemisorption of TBP+ is the weakest, yet notable decrease of HOR current density is still observed. The adsorption energies, ΔE, for TMA + , TBA + , and TBP + on Pt (111) surface from density functional theory are computed to be -2.79, -2.42 and -2.00 eV, respectively. The relatively low adsorption energy of TBP + is explained by the steric hindrance and electronic effect. This study emphasizes the importance of cationic group on HOR activity of alkaline anion exchange membrane fuel cells.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2016

A divalent cation-dependent variant of the glmS ribozyme with stringent Ca 2+ selectivity co-opts a preexisting nonspecific metal ion-binding site

Ribozymes use divalent cations for structural stabilization, as catalytic cofactors, or both. Because of the prominent role of Ca 2+ in intracellular signaling, engineered ribozymes with stringent Ca 2+ selectivity would be important in biotechnology. The wild-type glmS ribozyme (glmSWT) requires glucosamine-6-phosphate (GlcN6P) as a catalytic cofactor. Previously, a glmS ribozyme variant with three adenosine mutations (glm SAAA ) was identified, which dispenses with GlcN6P and instead uses, with little selectivity, divalent cations as cofactors for site-specific RNA cleavage. We now report a Ca 2+ -specific ribozyme (glmSCa) evolved from glm SAAA that is >10,000 times more active in Ca 2+ than Mg 2+ , is inactive in even 100 mM Mg2+, and is not responsive to GlcN6P. This stringent selectivity, reminiscent of the protein nuclease from Staphylococcus, allows rapid and selective ribozyme inactivation using a Ca 2+ chelator such as EGTA. Because glmSCa functions in physiologically relevant Ca 2+ concentrations, it can form the basis for intracellular sensors that couple Ca 2+ levels to RNA cleavage. Biochemical analysis of glmSCa reveals that it has co-opted for selective Ca 2+ binding a nonspecific cation-binding site responsible for structural stabilization in glmSWT and glmSAAA. Fine-tuning of the selectivity of the cation site allows repurposing of this preexisting molecular feature.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2023

Efficient Synthesis of High-Performance Anion Exchange Membranes by Applying Clickable Tetrakis(dialkylamino)phosphonium Cations

Tetrakis(dialkylamino)phosphonium (TKDAAP) compounds exhibit extraordinary base resistance, a prerequisite feature for high-performance anion exchange membranes (AEMs). It is, however, challenging to synthesize a TKDAAP compound with reactive functionality that can be used to link the cation to a polymer backbone. In this study, two TKDAAP compounds with alkyne functionality were synthesized and incorporated into an azide-modified SBS triblock copolymer backbone via Cu(I)-catalyzed alkyne–azide cycloaddition (CuAAC) “click” chemistry. The properties of the resulting AEMs were characterized. It was found that (1) the triazole linker between the cation and the polymer backbone was stable under alkaline conditions; (2) varying the substituents of TKDAAP compounds could dramatically alter the stability; and (3) increasing the hydrophilicity of the AEM was an efficient way to enhance its ionic conductivity. Using clickable TKDAAP compounds makes it easy to combine various cations into polymer backbones with adjustable cation content, thus potentially leading to an efficient way to screen a wide variety of polyelectrolyte structures to identify the most promising candidates for high-performance AEMs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2016

VUV PHOTO-PROCESSING OF PAH CATIONS: QUANTITATIVE STUDY ON THE IONIZATION VERSUS FRAGMENTATION PROCESSES

Interstellar polycyclic aromatic hydrocarbons (PAHs) are strongly affected by the absorption of vacuum ultraviolet (VUV) photons in the interstellar medium (ISM), yet the branching ratio between ionization and fragmentation is poorly studied. This is crucial for the stability and charge state of PAHs in the ISM in different environments, affecting in turn the chemistry, the energy balance, and the contribution of PAHs to the extinction and emission curves. We studied the interaction of PAH cations with VUV photons in the 7–20 eV range from the synchrotron SOLEIL beamline, DESIRS. We recorded by action spectroscopy the relative intensities of photo-fragmentation and photo-ionization for a set of eight PAH cations ranging in size from 14 to 24 carbon atoms, with different structures. At photon energies below ∼13.6 eV fragmentation dominates for the smaller species, while for larger species ionization is immediately competitive after the second ionization potential (IP). At higher photon energies all species behave similarly; the ionization yield gradually increases, leveling off between 0.8 and 0.9 at ∼18 eV. Among isomers, PAH structure appears to mainly affect the fragmentation cross section but not the ionization cross section. We also measured the second IP for all species and the third IP for two of them; all are in good agreement with theoretical ones, confirming that PAH cations can be further ionized in the diffuse ISM. Determining actual PAH dication abundances in the ISM will require detailed modeling. Our measured photo-ionization yields for several PAH cations provide a necessary ingredient for such models.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1994

Infrared spectroscopy of polycyclic aromatic hydrocarbon cations. 1: Matrix-isolated naphthalene and perdeuterated naphthalene

Ionized polycyclic aromatic hydrocarbons (PAHs) are thought to constitute an important component of the interstellar medium. Despite this fact, the infrared spectroscopic properties of ionized PAHs are almost unknown. The results we present here derive from our ongoing spectroscopic study of matrix isolated PAH ions and include the spectra of the naphthalene cation, C10H8(+), and its fully deuterated analog, C10D8(+), between 4000 and 200/cm. Ions are generated by in situ Lyman-alpha photoionization of the neutral precursor. Bands of the C10H8(+) ion are observed at 1525.7, 1518.8, 1400.9, 1218.0, 1216.9, 1214.9, 1023.2, and 758.7/cm. Positions and relative intensities of these bands agree well with those in the available literature. The 758.7/cm band has not previously been reported. C10D8(+) ion bands appear at 1466.2, 1463.8, 1379.4, 1373.8, 1077.3, 1075.4, and 1063.1/cm. Compared to the analogous modes in the neutral molecule, the intensities of the cation's CC modes are enhanced by an order of magnitude, while CH modes are depressed by this same factor. Integrated absorption intensities are calculated for the strongest bands of C10H8 and for the observed bands of C10H8(+). Absolute intensities derived for the naphthalene cation differ from earlier experimental results by a factor of approximately 50, and from theoretical predictions by a factor of approximately 300. Reasons for these discrepancies and from the astronomical implications of PAH cation spectra are discussed.

Hudgins, D. M.↗

NASA NTRS2019

Highly Accurate Quartic Force Field and Rovibrational Spectroscopic Constants for the Azirinyl Cation (c-C2NH2+) and Its Isomers

Azirinyl cation is an aromatic cyclic molecule that is isoelectronic with cyclopropenylidene, c-C3H2, and c-C3H3+. Cyclopropenylidene has been shown to be ubiquitous, existing in many different astrophysical environments. Given the similar chemistry between C and N, and the relative abundances between C and N in astrophysical environments, it is expected that there should be aromatic ringed molecules that incorporate N in the ring, but as yet, no such molecule has been identified. To address this issue, the present study uses high levels of electronic structure theory to compute a highly accurate quartic force field (QFF) for azirinyl cation and its two lowest lying isomers, the cyanomethyl and isocyanomethyl cations. The theoretical approach uses the singles and doubles coupled-cluster method that includes a perturbative correction for connected triple excitations, CCSD(T), together with extrapolation to the one-particle basis set limit and corrections for scalar relativity and core-correlation. The QFF is then used in a second order vibrational perturbation theory analysis (VPT2) to compute the fundamental vibrational frequencies and rovibrational spectroscopic constants for all three C2NH2+ isomers. The reliability of the VPT2 vibrational frequencies is tested by comparison to vibrational configuration interaction (VCI) calculations and excellent agreement is found between the two approaches. Fundamental vibrational frequencies and rovibrational spectroscopic constants for all singly substituted 13C, 15N, and D isotopologues are also reported. It is expected that the highly accurate spectroscopic data reported herein will be useful in the identification of these cations in high resolution experimental or astronomical observations.

Partha P Bera↗

DOE OSTI2013

Use of MgO doped with a divalent or trivalent metal cation for removing arsenic from water

Systems and methods for use of magnesium hydroxide, either directly or through one or more precursors, doped with a divalent or trivalent metal cation, for removing arsenic from drinking water, including water distribution systems. In one embodiment, magnesium hydroxide, Mg(OH).sub.2 (a strong adsorbent for arsenic) doped with a divalent or trivalent metal cation is used to adsorb arsenic. The complex consisting of arsenic adsorbed on Mg(OH).sub.2 doped with a divalent or trivalent metal cation is subsequently removed from the water by conventional means, including filtration, settling, skimming, vortexing, centrifugation, magnetic separation, or other well-known separation systems. In another embodiment, magnesium oxide, MgO, is employed, which reacts with water to form Mg(OH).sub.2. The resulting Mg(OH).sub.2 doped with a divalent or trivalent metal cation, then adsorbs arsenic, as set forth above. The method can also be used to treat human or animal poisoning with arsenic.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2017

Use of MgO doped with a divalent or trivalent metal cation for removing arsenic from water

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Ceramic cation exchange materials

Cation exchange membranes and materials including silica-based ceramics, and associated methods, are provided. In some aspects, cation exchange membranes that include a silica-based ceramic that forms a coating on and/or within a porous support membrane are described. The cation exchange membranes and materials may have certain structural or chemical attributes (e.g., pore size/distribution, chemical functionalization) that, alone or in combination, can result in advantageous performance characteristics in any of a variety of applications for which selective transport of positively charged ions through membranes/materials is desired. In some embodiments, the silica-based ceramic contains relatively small pores (e.g., substantially spherical nanopores) that may contribute to some such advantageous properties. In some embodiments, the cation exchange membrane or material includes sulfonate and/or sulfonic acid groups covalently bound to the silica-based ceramic.

Newbloom, Gregory Matthew↗

DOE OSTI2023

Mechanistic Insights into Copper(I) and Copper(II) Cation Exchange Reactions in CdSe Nanoplatelets

In this study, we investigated the synthesis of copper selenide nanoplatelets (NPLs) through a cation exchange reaction (CER) in 5-monolayer-thick CdSe NPLs using Cu(I) and Cu(II) precursors. We discovered that the exposure of CdSe NPLs to a Cu(I) precursor led to the transformation of NPLs into Cu 2-x Se while maintaining their nanoplatelet morphology. The replacement of Cd(II) with Cu(I) prevailed over the formation of doped structures. In the case of the Cu(II) precursor, we observed that Cu(II) was first reduced to Cu(I) before being intercalated into the host lattice, resulting in the synthesis of Cu 2-x Se, similar to CER with Cu(I) precursors but without preservation of the initial morphology of NPLs. Interestingly, the presence of oxygen was found to facilitate the cation exchange processes in CdSe NPLs, whereas a nitrogen atmosphere suppressed the CER. Further, despite the similar ionic sizes of Cu(I) and Cu(II), the substitution of Cd(II) with Cu(II) was found to be challenging, possibly due to the involvement of redox processes resulting in the significant deterioration of initial CdSe NPLs. We demonstrate that CER can achieve near-complete substitution of cadmium atoms with monovalent copper at room temperature. Understanding the processes involved in CERs is crucial for engineering more complex structures, such as high-entropy nanoparticles involving cation exchange with different oxidation states and development of material synthesis using machine learning and artificial intelligence approaches.

2D nanoplatelets↗

DOE OSTI2023

Combined Effects of Hemicolligation and Ion Pairing on Reduction Potentials of Biphenyl Radical Cations

Here, formal reduction potentials of highly oxidizing and short-lived radical cations of substituted biphenyls generated by pulse radiolysis in 1,2-dichloroethane (DCE) were measured using a redox equilibrium ladder method. The effect of halide ion–radical interactions on reduction potentials of biphenyls was examined by utilizing the ability of DCE to release Cl – in the vicinity of the radical cation. The Hammett correlation of measured potentials across a range of over 700 mV shows saturation at high Hammett sigma values. This effect has been explained by both ion-pairing and hemicolligation interactions between biphenyl radical cations and Cl – and appears to modulate reduction potentials by as much as 400 mV. This finding offers a convenient way to manipulate the energetics of electron transfer involving organic redox species.

14 SOLAR ENERGY↗

DOE OSTI2024

Enhancing Chiroptoelectronic Activity in Chiral 2D Perovskites via Chiral–Achiral Cation Mixing

Rational design of chiral two-dimensional hybrid organic–inorganic perovskites is crucial to achieve chiroptoelecronic, spintronic, and ferroelectric applications. Here, in this study, an efficient way to manipulate the chiroptoelectronic activity of 2D lead iodide perovskites is reported by forming mixed chiral (R- or S-methylbenzylammonium (R-MBA + or S-MBA + )) and achiral (n-butylammonium (nBA + )) cations in the organic layer. The strongest and flipped circular dichroism signals are observed in (R/S-MBA 0.5 nBA 0.5 ) 2 PbI 4 films compared to (R/S-MBA) 2 PbI 4 . Moreover, the (R/S-MBA 0.5 nBA 0.5 ) 2 PbI 4 films exhibit pseudo-symmetric, unchanged circularly polarized photoluminescence peak as temperature increases. First-principles calculations reveal that mixed chiral–achiral cations enhance the asymmetric hydrogen-bonding interaction between the organic and inorganic layers, causing more structural distortion, thus, larger spin-polarized band-splitting than pure chiral cations. Temperature-dependent powder X-ray diffraction and pair distribution function structure studies show the compressed intralayer lattice with enlarged interlayer spacing and increased local ordering. Overall, this work demonstrates a new method to tune chiral and chiroptoelectronic properties and reveals their atomic scale structural origins.

2D perovskites↗

DOE OSTI2023

Cation Disordered Anti-Perovskite Cathode Materials with Enhanced Lithium Diffusion and Suppressed Phase Transition

Recently, a new family of anti-perovskite Li 2 TMSO was discovered as promising cathode materials for Li-ion batteries (LIBs) with superiorities in high specific capacity, low cost, and environmental friendliness. However, the applications of these anti-perovskite materials meet severe challenges in the cyclability and rate performance. In this work, a cation-disordered anti-perovskite type solid solution Li 2 Fe 1– x Mn x SO (LFMSO, x = 0, 0.2, 0.5) with excellent electrochemical performance is reported. On the basis of comprehensive structural characterizations, the role of the cation disordering in LFMSO is clarified. In comparison with Li 2 FeSO (LFSO), the reduced Li-ion diffusion barrier and the increased Li-rich octahedral configurations in LFMSO with higher configurational entropy imply the facilitated long-range Li-ion diffusion and the suppressed phase transition, which favor the high-rate capability and cycling stability. In addition, the large lattice distortion and Coulombic interaction between the anions and cations lead to the breathing of the unit cell during charge/discharge. The variation of the unit cell volume decreases to 2.5% upon Li-ion delithiation. A superstructure is observed in LFMSO for the first time. These findings help to pave the way for the research and development of novel cathode materials for the next generation LIBs.

25 ENERGY STORAGE↗

DOE OSTI2020

Role of Redox-Inactive Transition-Metals in the Behavior of Cation-Disordered Rocksalt Cathodes

Owing to the capacity boost from oxygen redox activities, Li-rich cation-disordered rocksalts (LRCDRS) represent a new class of promising high-energy Li-ion battery cathode materials. Redox-inactive transition-metal (TM) cations, typically d 0 TM, are essential in the formation of rocksalt phases, however, their role in electrochemical performance and cathode stability is largely unknown. In the present study, the effect of two d 0 TM (Nb 5+ and Ti 4+ ) is systematically compared on the redox chemistry of Mn-based model LRCDRS cathodes, namely Li 1.3 Nb 0.3 Mn 0.4 O 2 (LNMO), Li 1.25 Nb 0.15 Ti 0.2 Mn 0.4 O 2 (LNTMO), and Li 1.2 Ti 0.4 Mn 0.4 O 2 (LTMO). Although electrochemically inactive, d 0 TM serves as a modulator for oxygen redox, with Nb 5+ significantly enhancing initial charge storage contribution from oxygen redox. Further studies using differential electrochemical mass spectroscopy and resonant inelastic X-ray scattering reveal that Ti 4+ is better in stabilizing the oxidized oxygen anions (O n- , 0 < n < 2), leading to a more reversible O redox process with less oxygen gas release. As a result, much improved chemical, structural and cycling stabilities are achieved on LTMO. Detailed evaluation on the effect of d 0 TM on degradation mechanism further suggests that proper design of redox-inactive TM cations provides an important avenue to balanced capacity and stability in this newer class of cathode materials.

25 ENERGY STORAGE↗

DOE OSTI2019

Modulation of Gas-Phase Lithium Cation Basicities by Microsolvation

In contrast to the extensive knowledge of lithium cation affinities and basicities, the thermochemistry of microsolvated lithium cations is much less explored. Here, we determine the relative stabilities of Li(A,B){sub n}{sup +} complexes, n = 2 and 3, by monitoring their gas-phase reactions with A and B substrate molecules, A/B = Me{sub 2}O, Et{sub 2}O, tetrahydrofuran, and MeCN, in a three-dimensional quadrupole-ion trap mass spectrometer. Kinetic analysis of the observed ligand displacement reactions affords equilibrium constants, which are then converted into Gibbs reaction energies. In addition, we use high-level quantum chemical calculations to predict the structures and sequential ligand dissociation energies of the homoleptic Li(A){sub n}{sup +} complexes, n = 1–3. As expected, the ligands dissociate more easily from complexes in higher coordination states. However, the very nature of the ligand also matters. Ligands with different steric demands can, thus, invert their relative Li{sup +} affinities depending on the coordination state of the metal center. This finding shows that microsolvation of Li{sup +} can result in specific effects, which are not recognized if the analysis takes into account only simple lithium cation affinities and basicities. .

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2017

ClbM is a versatile, cation-promiscuous MATE transporter found in the colibactin biosynthetic gene cluster

Multidrug transporters play key roles in cellular drug resistance to toxic molecules, yet these transporters are also involved in natural product transport as part of biosynthetic clusters in bacteria and fungi. The genotoxic molecule colibactin is produced by strains of virulent and pathobiont Escherichia coli and Klebsiella pneumoniae. In the biosynthetic cluster is a multidrug and toxic compound extrusion protein (MATE) proposed to transport the prodrug molecule precolibactin across the cytoplasmic membrane, for subsequent cleavage by the peptidase ClbP and cellular export. We recently determined the X-ray structure of ClbM, and showed preliminary data suggesting its specific role in precolibactin transport. Here, we define a functional role of ClbM by examining transport capabilities under various biochemical conditions. Our data indicate ClbM responds to sodium, potassium, and rubidium ion gradients, while also having substantial transport activity in the absence of alkali cations. - Highlights: • ClbM is a cation promiscuous MATE multidrug transporter. • The role of key residues were identified in both the cation and proton binding. • The biologically relevant substrate for ClbM is the natural product precolibactin.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2024

Engineering phonon transport through cation disorder in dimensionally constricted high entropy MXene

Designing materials with low thermal conductivity is a crucial objective for applications in thermal insulation and thermoelectrics. Traditional methods such as doping, mechanical strain and introducing defects in perfect crystals have been widely explored to impede the flow of heat. Here, this work introduces dimensional constriction and cationic disorder as novel avenues to manipulate lattice thermal conductivity (LTC). High entropy materials characterized by random distribution of multiple elements, creates a suitable environment for thermal insulation due to its configurational disorder and local lattice distortions. On the other hand, MXenes, derived from MAX-phase, have garnered considerable attention due to their unique structural attributes, leading to potential applications in catalysis and energy storage. Ti 2 AlC MAX-phase is examined to understand the impact of dimensional constriction on phonon transport of Ti 2 C with cationic disorder, i.e., (Ti 0.25 Nb 0.25 Cr 0.25 Ta 0.25 ) 2 C. The exponential reduction in LTC of HE-MXene is attributed to disorder scattering that significantly limits phonon mean free path (MFP) and relaxation time. The spread of mode-resolved LTC with MFP highlights the influence of disorder on phonon scattering. This work provides a systematic approach to engineer LTC through dimensional constriction and cationic disorder, laying the foundation for tailored materials with desired thermal properties.

2D materials↗