Dimethylammonium Addition to Halide Perovskite Precursor Increases Vertical and Lateral Heterogeneit
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Jariwala, Sarthak↗
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In Situ Studies of the Swelling by an Electrolyte in Electrochemical Doping of Ethylene Glycol-Substituted Polythiophene
Organic mixed ionic electronic conductors (OMIECs) have the potential to enable diverse new technologies, ranging from biosensors to flexible energy storage devices and neuromorphic computing platforms. However, a study of these materials in their operating state, which convolves both passive and potential-driven solvent, cation, and anion ingress, is extremely difficult, inhibiting rational material design. In this report, we present a novel approach to the in situ studies of the electrochemical switching of a prototypical OMIEC based on oligoethylene glycol (oEG) substitution of semicrystalline regioregular polythiophene via grazing-incidence X-ray scattering. Here by studying the crystal lattice both dry and in contact with the electrolyte while maintaining potential control, we can directly observe the evolution of the crystalline domains and their relationship to film performance in an electrochemically gated transistor. Despite the oEG side-chain enabling bulk electrolyte uptake, we find that the crystalline regions are relatively hydrophobic, exhibiting little (less than one water per thiophene) swelling of the undoped polymer, suggesting that the amorphous regions dominate the reported passive swelling behavior. With applied potential, we observe that the π–π separation in the crystals contracts while the lamella spacing increases in a balanced fashion, resulting in a negligible change in the crystal volume. The potential-induced changes in the crystal structure do not clearly correlate to the electrical performance of the film as an organic electrochemical transistor, suggesting that the transistor performance is strongly influenced by the amorphous regions of the film.
36 MATERIALS SCIENCE↗
Dynamics of Cation-Induced Conformational Changes in Nanometer-Sized Uranyl Peroxide Clusters
Conformational changes of the pyrophosphate (Pp)-functionalized uranyl peroxide nanocluster [(UO 2 ) 24 (O 2 ) 24 (P 2 O 7 ) 12 ] 48– ({U 24 Pp 12 }), dissolved as a Li/Na salt, can be induced by the titration of alkali cations into solution. The most symmetric conformer of the molecule has idealized octahedral ( O h ) molecular symmetry. One-dimensional 31 P NMR experiments provide direct evidence that both K + and Rb + ions trigger an O h -to- D 4 h conformational change within {U 24 Pp 12 }. Variable-temperature 31 P NMR experiments conducted on partially titrated {U 24 Pp 12 } systems show an effect on the rates; increased activation enthalpy and entropy for the D 4 h -to- O h transition is observed in the presence of Rb + compared to K + . Two-dimensional, exchange spectroscopy 31 P NMR revealed that magnetization transfer links chemically unique Pp bridges that are present in the D 4 h conformation and that this magnetization transfer occurs via a conformational rearrangement mechanism as the bridges interconvert between two symmetries. The interconversion is triggered by the departure and reentry of K (or Rb) cations out of and into the cavity of the cluster. This rearrangement allows Pp bridges to interconvert without the need to break bonds. Cs ions exhibit unique interactions with {U 24 Pp 12 } clusters and cause only minor changes in the solution 31 P NMR signatures, suggesting that O h symmetry is conserved. Single-crystal X-ray diffraction measurements reveal that the mixed Li/Na/Cs salt adopts D 2 h molecular symmetry, implying that while solvated, this cluster is in equilibrium with a more symmetric form. Thus, these results highlight the unusually flexible nature of the actinide-based {U 24 Pp 12 } and its sensitivity to countercations in solution.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Field-Driven Simulations to Probe the Impact of Ionic Correlations on Solution Transport Coefficients in Binary, Ternary, and Reciprocal Quaternary Aqueous Electrolytes
Ionic correlations play a critical role in governing transport properties of mixed-salt aqueous electrolyte solutions, yet their quantitative characterization remains challenging, particularly for multicomponent aqueous systems. Here, we develop a general nonequilibrium molecular dynamics framework to efficiently compute Onsager transport coefficients and ionic correlations in mixed-salt aqueous solutions. Using field-driven simulations, we obtain accurate Onsager matrices for LiCl/ KCl, KCl/KBr, and LiBr/KCl electrolyte solutions with significantly reduced computational cost relative to equilibrium Green−Kubo methods. The framework enables direct assessment of how attractive cation−anion and repulsive like-ion interactions contribute to conductivity and salt diffusivity across compositions. While static ion pairing exhibits strong composition dependence, dynamic ion correlations remain nearly invariant, leading to constant deviations from Nernst−Einstein predictions. These results highlight the disconnect between static ion association and dynamic transport correlations, and they establish a transferable approach for analyzing ion transport in complex electrolyte environments relevant to separation processes and electrochemical systems.
36 MATERIALS SCIENCE↗
Structure of Novel Phosphonium-Based Ionic Liquids with S and O Substitutions from Experiments and a Mixed Quantum-Classical Approach
This article presents experimental characterization information and synchrotron X-ray scattering measurements on a set of novel O- and S-substituted phosphonium-based ionic liquids (ILs) all coupled with the bis(fluorosulfonyl)imide (FSI-) anion. The ILs include the ethoxyethyltriethylphosphonium (P 222(2O2) + ) and triethyl[2-(ethylthio)ethyl]phosphonium (P 222(2S2) + ) cations, and we contrast results on these with those for unsubstituted triethylpentylphosphonium (P 2225 + ). The article also introduces a physics-based protocol that combines classical force field studies on larger simulation boxes with classical and first-principles studies on smaller boxes. The method produces significantly improved S(q) functions in the regime which in prior publications we have associated with inter- and intraionic adjacency correlations. By understanding which shorter-range structural changes improve S(q) in the q-regime of interest, we are also able to pinpoint specific deficiencies in the classical force field model. The approach we take should be quite general and could help study other complex liquids on different length scales.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
The Role of Dimethylammonium in Bandgap Modulation for Stable Halide Perovskites
Halide perovskites with bandgaps of 1.70–1.85 eV are of interest for multijunction photovoltaics. Mixing halides on the X site of the ABX3-structured perovskite system is a common way to reach these bandgaps, but this method introduces phase segregation pathways, limiting photovoltage. Recently, a new strategy for increasing the bandgap has been introduced, where cations normally too large to fit into the lattice, but compensated by smaller cations, are substituted on the A site. The mechanism underlying the increase of the bandgap with this strategy remained an open question. Here, we show that by partial substitution of the large dimethylammonium (DMA) cation at the A site of FA x Cs 1–x PbI y Br 3–y perovskites, a bandgap increase is observed not only when DMA is compensated by smaller Cs cations but also when only DMA is added, which is accompanied by an expansion of the crystal lattice. Our experimental findings suggest that adding DMA is causing an unexpected tilt in the perovskite octahedra, increasing the bandgap. Efficient solar cells based on 1.73 eV DMA-incorporated materials are extremely stable, retaining 96% of their original efficiency over 2200 h at 85 °C in the dark and 92% of their original efficiency after operation at 60 °C for 500 h. Finally, this octahedral tilting strategy is a promising route for attaining efficient and stable wide bandgap perovskite solar cells.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Dynamic Surface Reconstruction Unifies the Electrocatalytic Oxygen Evolution Performance of Nonstoichiometric Mixed Metal Oxides
Not Available
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Photoinduced iodide repulsion and halides-demixing in layered perovskites
Mixing halides in metal halide perovskites (MHPs) is an effective approach for adjusting the MHPs bandgap for applications in tandem solar cells. However, mixed-halide (MH-) MHPs undergo light-induced phase segregation (LIPS) under continuous illumination. Therefore, understanding the mechanism of LIPS is necessary for developing stable MH-MHPs. Here, we investigated LIPS in layered (L) MHPs and discovered a critical role of spacer cations in LIPS. Through probing chemical changes of LIPS, we unveil light-induced iodide repulsion and the formation of Br-rich-phase in illuminated regions during LIPS. This discovery also gives insight into the LIPS process in three-dimensional (3D) MHPs. By further investigating LIPS in 3D MHPs, we reveal that LIPS induces not only the formation of Br-rich and I-rich domains but also an overall change of halide distribution along the film thickness direction. Furthermore, LIPS is more significant in bulk due to a larger population of photogenerated charge carriers. Overall, this study reveals the chemical mechanism of LIPS in MHPs and its potential effect on device performance, offering insight into understanding the LIPS mechanism and improving the stability of MHPs.
36 MATERIALS SCIENCE↗
Deep Eutectic Solvent Formed by Imidazolium Cyanopyrrolide and Ethylene Glycol for Reactive CO 2 Separations
Solvents made from a reactive ionic liquid, with an imidazolium cation and pyrrolide anion, and ethylene glycol at a wide compositional range were studied for separations of CO 2 at low partial pressures (<<0.1 bar up to 1 bar). Thermal analysis and measurements of viscosity and density show compacting of the liquid upon mixing with enhanced stability achieved by hydrogen bonding. A detailed mechanistic study was performed by IR, quantitative NMR, and ab initio calculations that show significant CO 2 absorption capacity below 5000 ppm of CO 2 in N 2 . Three reversible routes are found that yield carbonate (major product), carboxylate (moderate), and carbamate (minor) species. With CO 2 at 100% RH, bicarbonate along with carbonate species form. The CO 2 -ethlyene glycol reaction complex, the carbonate anion, is stabilized by the hydrogen bonding and Coulombic interactions, thus preventing evaporation of the solvent during regeneration. This study demonstrates a promising approach to designer green solvents for CO 2 separations in open systems such as direct air capture.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Competing magnetic interactions and emergent phase diagrams in double perovskite Y 2 Ni x Co 1–x MnO 6
We present a comparative study of double perovskites Y 2 Ni x Co 1–x MnO 6 for x = 1, 0.5, and 0. The polycrystalline samples of Y 2 Ni x Co 1–x MnO 6 with space group P2 1 /n were synthesized via sol-gel technique. X-ray photoelectron spectroscopy (XPS) confirms the presence of majority Ni 2+ /Mn 4+ in Y 2 NiMnO 6 (YNMO) and a mixed valence state Ni 2+/3+ /Co 2+/3+ /Mn 4+/3+ in co-doped Y 2 Ni 0.5 Co 0.5 MnO 6 (YNCMO). The temperature dependent magnetization results suggest homogeneous substitution of Ni ions with Co ions with minimal contribution of 3+ cationic magnetic interactions in YNCMO. The superexchange ferromagnetic (FM) interaction has a major contribution to the magnetism of YNMO. The strength of antiferromagnetic (AFM) coupling resulting from the antiphase boundaries in Y 2 Ni x Co 1–x MnO 6 increases with the increase in the Co concentration. The AC susceptibility (AC-χ) study further validates the presence of higher density of antiphase boundaries, which is reflected by the dynamics of domain walls in YNCMO. The isothermal magnetic entropy change (ΔS M ) as functions of temperature and magnetic field is exploited to assess the stabilization of different magnetic phases. Finally, the findings of ΔS M (T,µ 0 H) lead to the proposed new magnetic phase diagrams for Y 2 Ni x Co 1–x MnO 6 for x = 1 and 0.5, in comparison with the previously established phase diagram of Y 2 CoMnO 6 .
36 MATERIALS SCIENCE↗
Selectivity of Electrochemical Ion Insertion into Manganese Dioxide Polymorphs
The ion insertion redox chemistry of manganese dioxide has diverse applications in energy storage, catalysis, and chemical separations. Unique properties derive from the assembly of Mn–O octahedra into polymorphic structures that can host protons and nonprotonic cations in interstitial sites. Despite many reports on individual ion-polymorph couples, much less is known about the selectivity of electrochemical ion insertion in MnO 2 . In this work, we use density functional theory to holistically compare the electrochemistry of A x MnO 2 (where A = H + , Li + , Na + , K + , Mg 2+ , Ca 2+ , Zn 2+ , Al 3+ ) in aqueous and nonaqueous electrolytes. We develop an efficient computational scheme demonstrating that Hubbard-U correction has a greater impact on calculating accurate redox energetics than choice of exchange-correlation functional. Using PBE+U, we find that for nonprotonic cations, ion selectivity depends on the oxygen coordination environments inside a polymorph. When H + is present, however, the driving force to form hydroxyl bonds is usually stronger. In aqueous electrolytes, only three ion-polymorph pairs are thermodynamically stable within water’s voltage stability window (Na + and K + in α-MnO 2 , and Li + in λ-MnO 2 ), with all other ion insertion being metastable. We find Al 3+ may insert into the δ, R, and λ polymorphs across the full 2-electron redox of MnO 2 at high voltage; however, electrolytes for multivalent ions must be designed to impede the formation of insoluble precipitates and facilitate cation desolvation. We also show that small ions coinsert with water in α-MnO 2 to achieve greater coordination by oxygen, while solvation energies and kinetic effects dictate water coinsertion in δ-MnO 2 . Finally, taken together, these findings explain reports of mixed ion insertion mechanisms in aqueous electrolytes and highlight promising design strategies for safe, high energy density electrochemical energy storage, desalination batteries, and electrocatalysts.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Structural Stability of Tin-Lead Halide Perovskite Solar Cells
One of the key features that makes halide perovskite solar cells such an attractive and intensely researched photovoltaic (PV) technology, is the tunability of the bandgap of these halide perovskite materials [1], [2]. Shortly after it was established that the bandgap could be increased to 1.7-1.8 eV, investigations into the application for silicon based tandem solar cells launched. Within a few years, conversion efficiencies of up to 28 % have been reported [3]. Concurrently, the interest in commercial application of this technology emerged and have rapidly increased. Whereas there are advantages to piggy backing on an established PV technology such as silicon, efforts to develop all-perovskite tandem solar cells are of considerable interest. Partly substituting the metal cation in the ABX3 perovskite enables the low bandgap absorbers required for an all-perovskite tandem solar cell. One common approach is to partially substitute the lead with tin, however these materials often suffered from poor stability. Therefore the development of an efficient, stable mixed tin-lead perovskite is key to enabling all-perovskite tandem solar cells.
degradation↗
Net Electronic Charge as an Effective Electronic Descriptor for Oxygen Release and Transport Properties of SrFeO 3 -based Oxygen Sorbents
Perovskite oxides, as oxygen sorbents, exhibit excellent potential in thermochemical redox applications such as chemical looping air separation (CLAS), resulting from their excellent redox properties and high tunability. The structural and compositional flexibility of perovskites, while making these mixed oxides highly versatile, also poses challenges for their design and optimization. Moreover, the elevated operating temperature and dynamic oxygen partial pressure swings during redox processes add additional complications for oxygen sorbent design. From a fundamental standpoint, finding simple yet effective descriptors for the effect of cation substitutions on oxygen sorbents’ redox and oxygen transport properties are of significant importance for rational optimization of perovskite-based oxygen sorbents. In the present study, a series of A/B-site-doped SrFeO 3-δ perovskites are investigated using density functional theory (DFT) + U simulations. From these simulations, an effective electronic structural descriptor, the net electronic charge (Δe) of oxygen anions, is extracted based on its excellent correlations with vacancy formation energy, experimentally derived oxygen capacity, and oxygen vacancy migration barrier. Overall, these findings provide an effective tool to correlate the oxygen sorbents’ redox performances with a simple yet physically meaningful descriptor for rational design and optimization of perovskites in the context of CLAS.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Cesium exhibits different mesoscale segregation and ion pairing than lithium, sodium, or potassium in concentrated alkaline aqueous nitrite solutions
Understanding ion pairing in concentrated alkaline electrolytes facilitates the prediction and control of chemical processes in nuclear waste. While sodium is the dominant alkali metal in such systems, cesium often exhibits distinct bulk behavior relative to lighter alkali cations. Aqueous mixtures of cesium hydroxide and sodium nitrite were compared to alkali hydroxide analogs using small-angle x-ray scattering, revealing that cesium disrupts the sodium nitrite electrolyte structure, forming cesium-rich domains. This mesoscale segregation contrasts with the near-ideal mixing observed in other mixed hydroxide–nitrite systems. Raman spectroscopy indicates cesium–nitrite ion pairing, evidenced by vibrational shifts distinct from those associated with sodium. Multinuclear magnetic resonance spectroscopy further supports cesium–nitrite and cesium–hydroxide association, revealing a distinct local environment for nitrite in cesium-containing solutions. Together, these findings show that cesium promotes a unique solution structure dominated by specific ion pairing within segregated domains. This structural organization may influence radical generation pathways in high-ionic-strength alkaline media relevant to nuclear waste processing and management.
Nienhuis, Emily T. [Pacific Northwest National Lab↗
Significance of Energy Conservation in Coupled-Trajectory Approaches to Nonadiabatic Dynamics
Practical methods for simulating photo-induced dynamics of molecules often rely on a trajectory-description of the nuclear dynamics, incorporating approximate electron-nuclear feedback. Through approximating electron–nuclear correlation terms in the exact factorization approach, trajectory-based methods have been derived and successfully applied to the dynamics of a variety of light-induced molecular processes, capturing quantum (de)coherence effects rigorously. These terms account for the coupling among the trajectories, recovering the nonlocal nature of quantum nuclear dynamics that is completely overlooked in traditional independent-trajectory algorithms. Nevertheless, some of the approximations introduced in the derivation of some of these methods do not conserve the total energy. We analyze energy conservation in the coupled trajectory mixed quantum-classical (CTMQC) algorithm and explore the performance of a modified algorithm, CTMQC-E, where some of the terms are redefined to restore energy conservation. Here, a set of molecular models is used as a test, namely, 2-cis-penta-2,4-dienimium cation, bis(methylene) adamantyl radical cation, butatriene cation, uracil radical cation, and neutral pyrazine.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
A competition between 2D and 3D magnetic orderings in novel mixed valent copper frameworks
Low-dimensional hybrid inorganic–organic frameworks exhibit high structural flexibility and allow for the inclusion of various magnetic and optically-active species into their host structures. The emergence of copper-based hybrid structures for various optical applications provides a promising foundation for exploring the integration of magnetic sublattices, paving the way for advancements in magneto-optical coupling and multifunctional materials. Herein, we introduce a novel class of hybrid copper frameworks with covalently-connected alternating magnetic 2D copper(II) formate and non-magnetic copper(I) bromide layers. The anionic framework is stabilized by A + cations to form ACu 5 Br 4 (COOH) 4 (A + = Na + , K + , Rb + , NH 4 + ) semiconductors (bandgaps 2.1–2.2 eV) with optical transitions suitable for optoelectronic applications. Comprehensive magnetometry studies show that ACu 5 Br 4 (COOH) 4 compounds exhibit low-dimensional 2D short-range antiferromagnetic order within the formate layers, characterized by strong exchange coupling (J/k B ∼ −100 K). Upon further temperature reduction, interactions between Cu(II) layers give rise to 3D long-range magnetic order at ∼40 K, despite the large (8.6–8.8 Å) spatial separation of the magnetic Cu(II) formate layers by nonmagnetic Cu(I)–Br bridging layers. This transition is further supported by electron paramagnetic resonance (EPR) spectroscopy. In conclusion, this study expands our understanding of low-dimensional hybrid frameworks and opens new avenues for the design of 2D multifunctional materials.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
On the early emergence of reverse transcription: theoretical basis and experimental evidence
Reverse transcriptase (RT) was first discovered as an essential catalyst in the biological cycle of retroviruses. However, in the past years evidence has accumulated showing that RTs are involved in a surprisingly large number of RNA-mediated transpositional events that include both viral and nonviral genetic entities. Although it is probable that some RT-bearing genetic elements like the different types of AIDS viruses and the mammalian LINE family have arisen in recent geological times, the possibility that reverse transcription first took place in the early Archean is supported by (1) the hypothesis that RNA preceded DNA as cellular genetic material; (2) the existence of homologous regions of the subunit tau of the E. coli DNA polymerase III with the simian immunodeficiency virus RT, the hepatitis B virus RT, and the beta' subunit of the E. coli RNA polymerase (McHenry et al. 1988); (3) the presence of several conserved motifs, including a 14-amino-acid segment that consists of an Asp-Asp pair flanked by hydrophobic amino acids, which are found in all RTs and in most cellular and viral RNA polymerases. However, whether extant RTs descend from the primitive polymerase involved in the RNA-to-DNA transition remains unproven. Substrate specificity of the AMV and HIV-1 RTs can be modified in the presence of Mn2+, a cation which allows them to add ribonucleotides to an oligo (dG) primer in a template-dependent reaction. This change in specificity is comparable to that observed under similar conditions in other nucleic acid polymerases. This experimentally induced change in RT substrate specificity may explain previous observations on the misincorporation of ribonucleotides by the Maloney murine sarcoma virus RT in the minus and plus DNA of this retrovirus (Chen and Temin 1980). Our results also suggest that HIV-infected macrophages and T-cell cells may contain mixed polynucleotides containing both ribo- and deoxyribonucleotides. The evolutionary significance of these changes in substrate specificities of nucleic acid polymerases is also discussed.
Non-NASA Center↗
Modulating coordinate site occupancy in high-entropy spinel electrocatalysts
High entropy spinel oxides provide a versatile platform for electrocatalysis because multiple metal cations can be incorporated into a single crystalline lattice, enabling tunable electronic structures. However, controlling how these cations distribute between tetrahedral and octahedral coordination sites remains a major challenge, limiting rational catalyst design. Here, we modulate cation coordination site occupancy between tetrahedral and octahedral sites in a Co–Fe–Cr–Mn–Ni framework by introducing a sixth cation (Zn, Ga, Mg, or Al) with distinct site preference energies. Using density functional theory, synchrotron X-ray absorption spectroscopy, and magnetic circular dichroism, we demonstrate that Zn preferentially occupies tetrahedral sites, driving increased octahedral occupancy of cobalt. This redistribution increases the population of octahedrally coordinated cobalt in mixed oxidation states, enhances electrical conductivity, and improves oxygen evolution reaction activity. Our findings establish coordination site occupancy as a critical design parameter, providing a strategic pathway for tailoring multicomponent spinel electrocatalysts with optimized performance.
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