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At least 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Exploring the influence of interfacial solvation on electrochemical CO 2 reduction using plasmon‐enhanced vibrational sum frequency generation spectroscopy

Although interfacial solvation plays an important role in determining carbon dioxide reduction (CO 2 R) kinetics, present understanding of the potential dependent properties of the electrochemical double layer under conditions relevant for CO 2 R remains limited. This article summarizes the development and recent applications of plasmon-enhanced vibrational sum frequency generation (VSFG) spectroscopy to study the effects of cation hydration and interfacial solvation on CO 2 R using CO as a vibrational Stark reporter. Results show that electrolyte cations retain their entire solvation shell upon adsorption to inactive sites, while active sites retain only a single water layer between the gold surface and the cation. Measurements also show that the total interfacial electric field can be separated into two contributions: one from the electrochemical double layer (Stern field) and another from the polar solvation environment (Onsager field). Surprisingly, correlating VSFG spectra with reaction kinetics reveals that it is the solvation-mediated Onsager field that governs the chemical reactivity at the electrode/electrolyte interface. Measuring the interfacial water spectra during electrocatalysis also provides evidence for the proton source during H2 evolution, which competes with CO 2 R in aqueous electrolyte. These findings highlight the importance of directly probing cation hydration and interfacial solvation, which mediates reaction kinetics at electrochemical interfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Solvent Acts as the Referee in a Match‐Up Between Charged and Preorganized Receptors

The prevalence of anion-cation contacts in biomolecular recognition under aqueous conditions suggests that ionic interactions should dominate the binding of anions in solvents across both high and low polarities. Investigations of this idea using titrations in low polarity solvents are impaired by interferences from ion pairing that prevent a clear picture of binding. To address this limitation and test the impact of ion-ion interactions across multiple solvents, we quantified chloride binding to a cationic receptor after accounting for ion pairing. In these studies, we created a chelate receptor using aryl-triazole CH donors and a quinolinium unit that directs its cationic methyl inside the binding pocket. In low-polarity dichloromethane, the 1 : 1 complex (log K 1 : 1 ~ 7.3) is more stable than neutral chelates, but fortuitously comparable to a preorganized macrocycle (log K 1 : 1 ~ 6.9). Polar acetonitrile and DMSO diminish stabilities of the charged receptor (log K 1 : 1 ~ 3.7 and 1.9) but surprisingly 100-fold more than the macrocycle. While both receptors lose stability by dielectric screening of electrostatic stability, the cationic receptor also pays additional costs of organization. Thus even though the charged receptor has stronger binding in apolar solvents, the uncharged receptor has more anion affinity in polar solvents.

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

Synergic regulation of mechanically interlocked molecules via lanthanide-contraction-based metal modulation and constituent ratios

A set of mechanically interlocked molecules (MIMs) can be synthesized efficiently using a one-pot procedure by selecting different trivalent lanthanide metal cations (M 3+ , M = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu) and adjusting the proportion of the reaction components. In this system, a flexible tetracationic macrocycle, often referred to as the “Texas-sized molecular box”, interacts with terephthalate dianions and trivalent lanthanide metal cations to form various structures. The transition from metal-organic rotaxane frameworks (MORFs) to metal-containing rotaxane supramolecular organic frameworks (RSOFs) is largely dictated by the lanthanide contraction effect, which leads to a decrease in the coordination number of the lanthanide ions. In addition, the nature of the MIMs within the MORFs can be fine-tuned by varying the ratio of the cation to the other components, allowing for additional control over the interlocked system. Furthermore, these findings demonstrate that the choice of metal cation and adjustments in the building block ratios component represent promising strategies for controlling the structures of MIM-based frameworks.

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

High-throughput measurements of CO 2 permeance and solubility in ionic liquid reveal a synergistic role of ionic interactions and void fractions

The factors that govern CO 2 solubility in ionic liquids (ILs) are of great interest for the development of new materials for CO 2 capture and utilization. The cationic functional group (i.e., imidazolium, pyrrolidinium, pyridinium, etc.), alkyl chain length of cation, degree of fluorination of anion, anion size, and the void fraction in IL are known to influence CO 2 solubility. However, a comprehensive explanation of how these factors collectively affect CO 2 solubility has not been developed yet. This knowledge gap is largely attributed to the lack of CO 2 solubility data for IL structures other than imidazolium based ILs. We report here an automated high-throughput (HT) setup for the measurement of CO 2 solubility in room-temperature ILs (RTILs) combining six different anions and nine different cations for a total of 19 different specific ranges of RTILs. The HT setup first dispenses up to 200 µL of RTILs in a 96-well microtiter plate and then utilizes a robotic arm to measure cyclic voltammogram (CV) in each well using maneuverable Ag electrodes. The Cottrell analysis of the CO 2 reduction CV peak provides a direct measurement of CO 2 permeance in RTILs, which yields Henry’s constant from the estimated diffusion coefficient of CO 2 . Henry’s constants thus obtained are in very good agreement with those reported earlier. The measured CO 2 permeance and Henry’s constant of all RTILs seem to follow a first-order dependence on void fraction and a second-order dependence on electrostatic interaction between anion and cation of IL, with some synergistic dependence on the product of a void fraction and electrostatic interaction, making them two important descriptors for the design of novel ILs.

CO2 Solubility↗
DOE OSTI2024

Enhanced pozzolanic reactivity in hydrogen-form zeolites as supplementary cementitious materials

Pozzolans rich in silica and alumina react with lime to form cementing compounds and are incorporated into portland cement as supplementary cementitious materials (SCMs). However, pozzolanic reactions progress slower than portland cement hydration, limiting their use in modern construction due to insufficient early-age strength. Hence, alternative SCMs that enable faster pozzolanic reactions are necessary including synthetic zeolites, which have high surface areas and compositional purity that indicate the possibility of rapid pozzolanic reactivity. Synthetic zeolites with varying cation composition (Na-zeolite, H-zeolite), SiO 2 /Al 2 O 3 ratio, and framework type were evaluated for pozzolanic reactivity via Ca(OH) 2 consumption using ion exchange and in-situ X-ray diffraction experiments. Na-zeolites exhibited limited exchange reactions with KOH and Ca(OH) 2 due to the occupancy of acid sites by Na + and hydroxyl groups. Meanwhile, H-zeolites readily adsorbed K + and Ca 2+ from a hydroxide solution by exchanging cations with H + at Brønsted acid sites or cation adsorption at vacant acid sites. By adsorbing cations, the H-zeolite reduced the pH and increased Ca 2+ solubility to promote pozzolanic reactions in a system where Ca(OH) 2 dissolution/diffusion was a rate limiting factor. High H-zeolite reactivity resulted in 0.8 g of Ca(OH) 2 consumed per 1 g of zeolites after 16 h of reaction versus 0.4 g of Ca(OH) 2 consumed per 1 g of Na-zeolite. The H-zeolite modulated the pore fluid alkalinity and created a low-density amorphous silicate phase via mechanisms analogous to two-step C-S-H nucleation experiments. Finally, controlling these reaction mechanisms is key to developing next generation pozzolanic cementitious systems with comparable hydration rates to portland cement.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Hybrid bilayered vanadium oxide electrodes with large and tunable interlayer distances in lithium-ion batteries

The interlayer distances in layered electrode materials, influenced by the chemical composition of the confined interlayer regions, have a significant impact on their electrochemical performance. Chemical preintercalation of inorganic metal ions affects the interlayer spacing, yet expansion is limited by the hydrated ion radii. Herein, we demonstrate that using varying concentrations of decyltrimethylammonium (DTA + ) and cetyltrimethylammonium (CTA + ) cations in chemical preintercalation synthesis followed by hydrothermal treatment, the interlayer distance of hybrid bilayered vanadium oxides (BVOs) can be tuned between 11.1 Å and 35.6 Å. Our analyses reveal that these variations in interlayer spacing are due to different amounts of structural water and alkylammonium cations confined within the interlayer regions. Increased concentrations of alkylammonium cations not only expand the interlayer spacing but also induce local bending and disordering of the V-O bilayers. Electrochemical cycling of hybrid BVO electrodes in non-aqueous lithium-ion cells show that specific capacities decrease as interlayer regions expand, suggesting that the densely packed alkylammonium cations obstruct intercalation sites and hinder Li + ion transport. Furthermore, we found that greater layer separation facilitates the dissolution of active material into the electrolyte, resulting in rapid capacity decay during extended cycling. In conclusion, this study emphasizes that layered electrode materials require both spacious interlayer regions as well as high structural and chemical stabilities, providing guidelines for structural engineering of organic–inorganic hybrids.

25 ENERGY STORAGE↗
DOE OSTI2021

Structural and spectral studies of hydrated hexaamminecobalt(III)–hexafluororhenate(IV)

The crystal structure of the [Co(NH 3 ) 6 ] 2 [ReF 6 ] 3 ·3H 2 O (I) salt is reported. The salt crystallizes in the trigonal space group P31m with the following unit cell dimensions: a = 15.8714(4) Å, b = 15.8714(4) Å, and c = 9.8657(4) Å. Here, the structure of (I) consists of [Co(NH 3 ) 6 ] 3+ cations, [ReF 6 ] 2– anions, and co-crystallized water molecules which are linked by hydrogen bonding. In (I), independent [ReF 6 ] 2– anions and [Co(NH 3 ) 6 ] 3+ cations octahedron are slightly distorted. Characteristic vibration bands of the [Co(NH 3 ) 6 ] 3+ cation, [ReF 6 ] 2– anion as well as the co-crystallized H 2 O molecules are observed in the infrared spectra of (I). UV-Visible analyses in water showed that the absorption of the [Co(NH 3 ) 6 ] 3+ cation predominate the spectra of (I).

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2020

Moderate pH changes alter the fluxes, selectivities and limiting currents in ion transport through polyelectrolyte multilayers deposited on membranes

Layer-by-layer (LBL) polyelectrolyte coatings on membranes are attractive for their high selectivities between monovalent and divalent ions. However, deposition of poly(4-styrenesulfonate) (PSS)/protonated poly(allylamine) (PAH) films on ion-exchange membranes leads to low ion fluxes that restrict productivity or current efficiency. This study shows that increasing the solution pH from 6.5 to 8.3 enhances cation fluxes and limiting currents through (PAH/PSS) 5 PAH-coated cation-exchange membranes while still achieving order of magnitude selectivity increases compared to bare membranes. In Donnan dialysis through (PAH/PSS) 5 PAH-coated Nafion, at pH 8.3 the K + /Mg 2+ selectivity is 100, and the K + flux is 22 times that at pH 6.5. Moreover, at the higher pH the electrodialysis limiting current through these membranes increases ~5-fold. This enables electrodialysis separation of K + and Mg 2+ with a current efficiency around 0.75, a selectivity of 18, and 50% K + recovery from the source phase. Transmembrane potential measurements and increases in Cl - /SO 4 2- selectivities (from 9.5 at pH 6.5 to ~70 at pH 8.3) for porous alumina membranes coated with (PSS/PAH) 5 PSS films suggest that the coating becomes cation-permselective at higher pH. Increased cation transference numbers in polyelectrolyte coatings likely lead to the enhanced limiting currents for coated Nafion at higher pH. Lastly, (PAH/PSS) 5 PAH-coated Nafion shows a Li + /Mg 2+ Donnan dialysis selectivity >700 at neutral pH and a selectivity of 10 at pH 8.3. However, the Li + flux is 6 times greater at pH 8.3, which might make operation at the higher pH desirable.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Crystal structure of meglumine diatrizoate, (C 7 H 18 NO 5 )(C 11 H 8 I 3 N 2 O 4 )

The crystal structure of meglumine diatrizoate has been solved and refined using synchrotron X-ray powder diffraction data and optimized using density functional theory techniques. Meglumine diatrizoate crystallizes in space group P2 1 (#4) with a = 10.74697(4), b = 6.49364(2), c = 18.52774(7) Å, β = 90.2263(3), V = 1292.985(5) Å 3 , and Z = 2. Two different crystal structures, which yielded essentially identical refinement residuals and positions of the non-H atoms, were obtained. The differences were in the H atom positions and the hydrogen bonding. One structure was 123.0 kJ/mol/cell lower in energy than the other and was adopted for the final description. The crystal structure consists of alternating double layers of cations and anions along the c-axis. The hydrogen bonds link the cations and anions into a three-dimensional framework. Each of the hydrogen atoms on the ammonium nitrogen of the cation acts as a donor in a strong N–H∙∙∙O hydrogen bond. One of these is to a hydroxyl group of another cation, and the other is to the carboxylate group of the anion. Each of the amide nitrogen atoms of the anion forms a strong N–H∙∙∙O intermolecular hydrogen bond, one to a carbonyl and the other to a carboxylate group. The powder pattern has been submitted to ICDD for inclusion in the Powder Diffraction File™ (PDF®).

36 MATERIALS SCIENCE↗
DOE OSTI2022

Selective Crystallization for Green Separations of Lanthanides Using 5-(Pyrimidyl)Tetrazolate

In an effort to develop facile, low-cost, and environmentally benign separations of lanthanides, the coordination chemistry and selective crystallization of Ln 3+ cations with the water-soluble ligand 5-(pyrimidyl)tetrazolate (pmtz) have been investigated. The wide range of coordination modes of pmtz allows for discrimination between these cations, and five distinct compound types can be prepared that are dependent on the lanthanide employed. La 3+ leads to the formation of [La(pmtz) 2 (H 2 O) 6 ]Cl (S1). [Ln(pmtz) 3 (H 2 O) 3 ]·(3+n)H 2 O is obtained with Ce 3+ and Pr 3+ (S2). Ce 3+ can also form [(Ce(pmtz) 2 (H 2 O) 3 ) 2 (μ-pmtz)](pmtz)·11H 2 O (S3). [(Ln(pmtz) 2 (H 2 O) 3 ) 2 (μ-pmtz)] 2 (pmtz) 2 ·14H 2 O (S4) is formed with Nd 3+ and Sm 3+ . Here, the smaller Ln 3+ cations, Dy 3+ to Lu 3+ , all yield [Ln(H 2 O) 8 ](pmtz) 3 ·3H 2 O (S5). This selective crystallization of Ln 3+ cations based primarily on ionic radii provides a simple method for achieving group separations.

Bai, Zhuanling↗
DOE OSTI2024

Two Spacers, One Perovskite: Integrating Ruddlesden–Popper and Dion–Jacobson Halide Perovskites

Hybrid organic–inorganic perovskites are a rapidly developing class of materials due to their desirable properties for optoelectronic applications such as their ease of synthesis, solution-processable film formation, tunable band gap, strong photoluminescence, good charge carrier mobilities, and high defect tolerance. Here, we present a novel 2D perovskite motif that seamlessly integrates the structural elements from both Ruddlesden–Popper and Dion–Jacobson halide perovskites. We demonstrate the incorporation of two different organic spacer cations in an ordered manner in 5 novel 2D perovskite iodide materials. Both a cyclic diammonium cation 3-(aminomethyl)piperidinium (3AMP) and a linear alkyl monoammonium cation (Cn = C n H 2n+4 N, n = 4–8) are present in distinct alternating layers, making the new series (Cn) 2 (3AMP)[PbI 4 ] 2 . The crystallization of these materials was optimized through careful temperature control to obtain precise crystal structures via single-crystal X-ray diffraction (XRD) which confirmed the presence of the two cations in distinct layers. The influence of the two spacers on optical properties including the band gaps and photoluminescence spectra are found to more closely resemble (3AMP)PbI 4 than (Cn) 2 PbI 4 , which can be attributed to the amount of distortion imposed by the 3AMP spacer on the lead iodide layers. The findings are supported by density functional theory calculations. The strong photoelectric response of solution-processed thin films shows the potential of these materials in photodetectors or photovoltaics. This unprecedented amalgamation of RP–DJ in (Cn) 2 (3AMP)[PbI 4 ] 2 in a structurally ordered fashion suggests a potential vastly underexplored phase space of 2D perovskites in which there are chemically different spacers in distinct layers of the structure, providing an additional parameter to tune perovskite properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Selective Ion Enrichment and Charge Storage through Transport Hysteresis in Conical Nanopipettes

Greater selectivity and controls in the ion transport dynamics are essential in fields such as charge storage, separation, energy storage and conversion, neuromorphic computing and learning, electrochemistry, to name a few. Mechanistic insights into the intriguing hysteresis effects in the rectified electrokinetic transport through single conical nanopipettes are unveiled by combining time-resolved electroanalytical experiments with numeric simulation. Cations as counterions for surface charges are found to dominate not just the through-nanopore flux but also the hysteresis charges, that is, the net enriched or expelled charges during the transport process. Built on our earlier report on the through-nanopore ion flux dominated by counterions for surface charges, the “trapped ions” or hysteresis charges are analyzed herein. Cation selectivity is almost 100% in the hysteresis charges during the potential scans in low conductivity states driven by the combined applied and intrinsic surface electrical fields. Surprisingly, the cation selectivity in the total hysteresis charges remains high at 70–80% over a wide bulk concentration range in the high conductivity (HC) states, where higher ionic strength due to ion enrichment would decrease electrostatistic effects and thus ion selectivity. The retained high selectivity at HC is explained by the competition effects of electroosmotic flow against the co-ion migration. Furthermore, the respective cation and anion portions in the total hysteresis charges over a wide range of ionic strength and measurement conditions provide generalizable strategies for improvements in both transport throughput and selectivity.

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

Competitive Sorption of H 2 O and CO 2 in Clay Mineral Interlayers

The first-reported competitive CO 2 –H 2 O sorption isotherms on a naturally occurring expandable clay mineral (saponite) exchanged with Na, K, and Cs at near ambient CO 2 concentrations (1% CO 2 ) are reported by combining ATR-FTIR spectroscopy with gravimetric sorption methods. Little CO 2 sorption was observed at high relative humidity (RH) but increased significantly at low RH. Unlike prior work where CO 2 sorption was reported on samples that were previously subjected to heating and/or evacuation treatment to remove sorbed H 2 O, this study manipulated CO 2 sorption by controlling RH. CO 2 sorption increased in the order Cs- > K- > Na-exchanged saponite and was anticorrelated with the Gibbs energy of hydration of the exchangeable cation. As expected, H 2 O sorption followed the opposite trend, with increased H 2 O sorption occurring in the order Na > K > Cs. The amount of CO 2 sorbed using 1 atm CO 2 (p/p o = 1.0) ranged from 50 to 30 mg CO 2 /g clay and from 1.25 to 0.8 mg CO2 /g clay for 1% CO 2 (p/p o = 0.01) in N 2 . The sensitivity of the ATR-FTIR measurements is demonstrated by detecting the CO 2 stretch of adsorbed CO 2 from air containing 500 ppmv CO 2 . The spectral features of sorbed CO 2 were minimally affected by the nature of the exchangeable cation or variations in H 2 O content. However, the position of the HOH bending band shifted significantly from 1638 to 1610 cm –1 as H 2 O content decreased, reflecting changes in intermolecular hydrogen bonding between H 2 O molecules in the saponite interlayer. The shift in position of the HOH bending band to lower energy was coincident with increased CO 2 sorption. CO 2 sorption in clay mineral interlayers is consistent with sorption on weakly hydrated partially hydrophobic sites found on low charge density smectites and is enhanced by lower RH and by the presence of weakly hydrated exchangeable cations like Cs + or K + . In conclusion, the greatest CO 2 sorption occurs on Cs-saponite because this is the least hydrated cation of the three used in the study and indicates that CO2 sorption occurs on the neutral portion of the siloxane surface.

Johnston, Cliff T. [Purdue Univ., West Lafayette, ↗
DOE OSTI2023

Electric-Field-Induced Assembly of an Ionic Liquid–Water Interphase Enables Efficient Heavy Metal Electrosorption

Controlling ion desolvation, transport, and charge transfer at the electrode-electrolyte interface (EEI) is critical to enabling the rational design of efficient and selective separation of targeted heavy metals and decontamination of industrial waste water. One challenge is to sufficiently resolve and interrogate the intermediate transformation steps between solvated metal cations and bare cations for electroreduction at the EEI and establish pathways to modulate these steps to achieve efficient energy transfer for targeted reactive separations. Herein, we obtained a predictive understanding of the effect of adding a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium chloride (EMIMCl), to an aqueous electrolyte on modulating the desolvation and electrosorption of Pb 2+ cations using a combination of experimental and theoretical techniques. Here, we reveal formation of a compact interphase layer consisting of EMIMCl-Pb complex clusters under an applied electric field using operando electrochemical Raman spectroscopy, atomic force microscopy, and electrochemical impedance spectroscopy measurements combined with classical molecular dynamics simulations. The application of a larger negative potential is shown to result in formation of a well oriented layer with the positive imidazolium ring of the EMIMCl lying on the electrode and the long hydrophobic alkyl chain extending into the bulk electrolyte. This oriented layer is demonstrated to facilitate desolvation of incoming solvated Pb 2+ cations and decrease the charge transfer resistance for Pb electrodeposition, which has important implications for selective removal of Pb from contaminated mixtures. Overall, our studies open up new opportunities to modulate ion desolvation using hydrophobic ionic liquids in aqueous electrolytes for efficient heavy metal separation.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Understanding the Conductivity and Transference Trade-Off in Polymer Electrolytes Using a Robeson-Inspired Upper Bound

The development of high-performance electrolytes is crucial for advancing next-generation lithium and sodium battery technologies. Since the cation is the working ion in both technologies, electrolytes exhibiting the rapid cation transport are essential for making progress. Pathways to optimize electrolytes are unclear due to the inherent trade-off between conductivity and cation transference. While this trade-off is sometimes recognized, there are no well-accepted methodologies for quantifying it. Inspired by the Robeson upper bound for the permeability–selectivity trade-off in gas separation membranes, we propose an approach for quantifying the trade-off in electrolytes using Newman’s concentrated solution theory. We suggest calling this the Newman upper bound. By analyzing published data from 30 polymer electrolytes containing univalent lithium and sodium salts, the Newman upper bound is expressed as κ = 2.0­(1/ρ+ – 1) where κ (mS/cm) is conductivity and ρ+ is the current fraction measured in a symmetric cell as first described by Bruce et al. [J. Electroanal. Chem. Interfacial Electrochem. 1987, 225 (1), 1–17]. This formulation of the upper bound introduces a critical guiding metric for designing next-generation polymer electrolytes; it highlights factors underlying the trade-off, including the salt diffusion coefficient (D), cation transference number relative to solvent velocity ( t + 0 ), and thermodynamic factor (1 + (d lnγ+–)/(d lnm)), where γ+– is the mean molar activity coefficient and m is the molality. These parameters have been measured for very few electrolytes. We posit that establishing the molecular properties that govern these parameters will lead to improved electrolytes that greatly exceed the current upper bound.

He, Zirong↗
DOE OSTI2024

Ramifications of Ion Migration in 2D Lead Halide Perovskites

Lower dimensional or 2D halide perovskites with their versatile structural and functional properties, are known to improve the performance and room temperature stability of perovskite solar cells. One would expect 2D perovskites to be more resistant to ion migration compared to their 3D counterparts because of the presence of bulky organic cations. However, recent findings show ion migration indeed is prevalent in 2D halide perovskites similar to 3D perovskites. Halide ion migration in 2D perovskites manifests itself as halide ion segregation under photoirradiation as well as in halide exchange between physically paired films of 2D perovskites with different halide ions. Besides halide ion migration, cation migration of spacer cations and A-site cation is also seen when 2D/3D perovskite films are subjected to light and thermal stress. It is important to recognize the importance of ion migration while incorporating 2D perovskites in solar cells and other optoelectronic devices as it can be detrimental for achieving streamlined performance and long-term stability Furthermore, this perspective discusses recent reports on ion migration in 2D and in 2D/3D halide perovskite films under the operational conditions (at elevated temperature and given in-built bias) and presents a few mitigating strategies.

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

Unraveling the Combined Photothermal Stability of Common Perovskite Solar Cell Compositions

In halide perovskite solar cells, certain compositions, especially those with a high mixture of anions, degrade rapidly. Here, in this study, a degradation study compares the photo (exposure to light), thermal (exposure to elevated temperatures), and photo-plus-thermal (combination) stability of three representative perovskite compositions chosen for their relatively high performance and to independently test anion versus cation effects. Based upon experience and reports, the compositions studied are triple cation with a high Br ratio (Cs 0.05 (FA 0.98 MA 0.02 ) 0.95 Pb(I 0.5 Br 0.5 ) 3 ), all iodide with a moderately high Cs ratio (FA 0.8 Cs 0.2 PbI 3 ), and FA-dominated triple cation (Cs 0.05 (FA 0.98 MA 0.02 ) 0.95 Pb(I 0.98 Br 0.02 ) 3 ). Cs 0.05 (FA 0.98 MA 0.02 ) 0.95 Pb(I 0.98 Br 0.02 ) 3 displayed the best combined photo-plus-thermal stability. Degradation mechanisms were investigated by comparing the morphology, surface composition, and bulk and interface carrier dynamics. Under the harshest aging conditions (photo-plus-thermal), phase segregation and vaporization of organic cations occurred, along with the appearance of high-energy states indicating the interaction with C 60 . The findings were verified on perovskite films blade-coated in air used in devices (FTO/NiOx/SAM/Perovskite/C 60 /BCP/Cu), achieving an efficiency of 21.9% alongside correlated stability.

14 SOLAR ENERGY↗
DOE OSTI2024

Chemical Environment and Structural Variations in High Entropy Oxide Thin Film Probed with Electron Microscopy

For this work, we employ analytical transmission electron microscopy (TEM) to correlate the structural and chemical environment variations within a stacked epitaxial thin film of the high entropy oxide (HEO) Mg 0.2 Co 0.2 Ni 0.2 Cu 0.2 Zn 0.2 O (J14), with two layers grown at different substrate temperatures (500 and 200 °C) using pulsed laser deposition (PLD). Electron diffraction and atomically resolved STEM imaging reveal the difference in out-of-plane lattice parameters in the stacked thin film, which is further quantified on a larger scale using four-dimensional STEM (4D-STEM). In the layer deposited at a lower temperature, electron energy loss spectroscopy (EELS) mapping indicates drastic changes in the oxidation states and bonding environment for Co ions, and energy-dispersive X-ray spectroscopy (EDX) mapping detects more significant cation deficiency. Ab initio density functional theory (DFT) calculations validate that vacancies on the cation sublattice of J14 result in significant electronic and structural changes. The experimental and computational analyses indicate that low temperatures during film growth result in cation deficiency, an altered chemical environment, and reduced lattice parameters while maintaining a single phase. Our results demonstrate that the complex correlation of configurational entropy, kinetics, and thermodynamics can be utilized for accessing a range of metastable configurations in HEO materials without altering cation proportions, enabling further engineering of functional properties of HEO materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗