118 Search Results

Current efforts to integrate CO2 capture and electrochemical conversion (reactive capture) are often performed under aqueous conditions, resulting in undesired hydrogen evolution and reliance on precious metal catalysts and pure CO2 streams. Here we explore reactive capture in aprotic media. By shifting the amine–CO2 adduct speciation to carbamic acid (instead of carbamate) in dimethyl sulfoxide, we increased CO2 uptake threefold compared with an aqueous medium, suppressing hydrogen evolution and supporting a 78% Faradaic efficiency towards CO over an earth-abundant zinc catalyst. Under simulated high-oxygen-content flue gas (17% CO2, 17% O2, 66% N2), we also obtained up to 43% CO Faradaicmore » efficiency over multiple capture–conversion cycles. Our findings showcase the confluence of reactant speciation, electrolyte composition and electrocatalyst design in enabling selective and active electrochemical transformations.« less

Computational studies of CO 2 reduction to yield various products were carried out on the basal plane and edges of different MXene materials. The impact of vacancies upon Mo 2 TiC 2 T x, W 2 TiC 2 T x, and Ti 3 C 2 T x (T x = O and OH) was also examined for both edge and basal sites. Initial calibrations were carried out to generate surfaces with optimal oxide/hydroxide ratios and proper termination sites upon which various vacancy sites were explored to ensure an accurate model of the surfaces’ resting states. From this work, Mo 2more » TiC 2 O was determined to exhibit the lowest theoretical overpotential for methane as determined by volcano plot analyses. At a large enough vacancy concentration, the CO 2 reduction reaction (CO 2 RR) is predicted to outcompete the hydrogen evolution reaction (HER) as the predominant reaction on the surface. When examining the edge of Mo 2 TiC 2 O, stronger CO 2 binding was exhibited to such an extent that the reaction was predicted to terminate after the generation of formate on the edge.« less

Understanding the distinct roles of lithium ions (Li+) and lithium polysulfide intermediates, Li2Sx (LiPS) is critical for designing electrolytes that can extend the practical cycle life of lithium–sulfur (Li–S) batteries. In this work, we decouple the solvation and solubility effects of Li+ and LiPS and correlate them with electrochemical performance through a cosolvent strategy. Li+ solubility and solvation primarily dictate the electrolyte’s ionic conductivity and the reversibility of lithium anode stripping/plating. In contrast, LiPS solvation governs the thermodynamics of sulfur (S8), LiPS, and lithium sulfide (Li2S) interconversion, while the LiPS solubility determines their redox kinetics. By employing a fluorinated–glyme (F-glyme)more » cosolvent, specifically 1,2-bis(2,2-difluoroethoxy)ethane (F4DEE), that exhibits low LiPS solubility yet moderate Li+ solvation, we designed an electrolyte that enhances lithium anode stability while maintaining sufficient sulfur cathode kinetics, thereby prolonging Li–S cell cycle life. This study provides mechanistic insights into the interplay between Li+ and LiPS in Li–S electrochemistry and offers design principles for next-generation electrolytes for Li–S batteries.« less

Area selective atomic layer deposition (AS-ALD) is a bottom-up synthesis approach with potential for deposition with molecular level precision. The site-specific hydration of metal oxide substrates, combined with surface H2O-selective ALD processes, provides a potentially powerful path to targeted synthesis. Density functional theory (DFT) calculations are used to predict the thermodynamics of ALD precursor reactivity and hydration for (001), (101), (110), and (100) rutile SnO2 facets as a function of temperature. Trimethylaluminum (TMA) and dimethyl aluminum isopropoxide (DMAI) dimers are predicted to react with both dehydrated and hydrated SnO2 (001), (101), and (110) facets at ALD-relevant temperatures, while the SnO2more » (100) facet is predicted to be uniquely unreactive with TMA and DMAI monomers as well as dehydrate near 177 °C making this facet more amenable to targeted ALD. In situ ellipsometric studies of Al2O3 ALD on polycrystalline SnO2 at 150 °C are consistent with the computational predictions of rapid and unselective nucleation, in stark contrast to inhibited and selective ALD on isostructural rutile TiO2.« less

Atomically dispersed Fe-N-C catalysts with high oxygen reduction reaction (ORR) activity have attracted great attention since the last decade. Due to comparable ORR activity and low material cost, they are promising platinum group metal (PGM)-free catalysts that can replace the commercialized Pt/C materials; furthermore, it can facilitate the efficiency of the fuel cell technologies and mitigate dependence on fossil fuels. Great advancements have been made to experimentally optimize the synthesis approach of the Fe-N-C catalysts, enhance the ORR activity, and improve the catalyst stability. Similarly, recent theoretical studies also provide enriched understanding of the active site structures, properties, and reactionmore » mechanisms. In this review, discussions are made upon utilizing combined experimental and computational spectroscopy to reveal the active site structures, employing mechanistic studies to investigate reaction thermodynamics and kinetics, as well as developing scaling relationships to assist the design and development of future PGM-free catalyst materials. Furthermore, recent advances in studying Fe-N-C catalysts utilizing electrified surface models and explicit solvation models are also discussed. Not only can these aspects improve the accuracy of theoretical simulation and predictions but also deepen the understanding of the catalyst properties and reaction mechanisms under the effect of surface charges and solvent molecules.« less

Traditional ethylene carbonate (EC)-based electrolytes exhibit strong solvation power at the surface of the layered transition metal oxide cathodes, which accelerates transition metal dissolution. The subsequent migration and deposition of dissolved transition metal species on the anode surface lead to significant capacity fading. To overcome this challenge, we report a weakly solvating, all-fluorinated electrolyte designed to mitigate transition metal dissolution. For the first time, the role of electrolyte solvation in suppressing transition metal dissolution is systematically investigated. The tailored electrolyte significantly reduces transition metal dissolution and enhances the electrochemical performance of Li- and Mn-rich (LMR) cathode/graphite cells. This solvation-modulating strategymore » offers a broadly applicable framework for stabilizing interphases in other earth-abundant cathode chemistries, which similarly demand kinetic protection against interfacial degradation.« less

M-edge X-ray absorption spectroscopy (XAS), which probes 3p→3d transitions in first-row transition metals, provides detailed insights into oxidation states, spin-states, and local electronic structure with high element and orbital specificity. Operating in the extreme ultraviolet (XUV) region, this technique provides sharp multiplet-resolved features with high sensitivity to ligand field and covalency effects. Compared to K- and L-edge XAS, M-edge spectra exhibit significantly narrower full widths at half maximum (typically 0.3–0.5 eV versus >1 eV at the L-edge and >1.5–2 eV at the K-edge), owing to longer 3p core-hole lifetimes. M-edge measurements are also more surface-sensitive due to the lower photonmore » energy range, making them particularly well-suited for probing thin films, interfaces, and surface-bound species. The advent of tabletop high-harmonic generation (HHG) sources has enabled femtosecond time-resolved M-edge measurements, allowing direct observation of ultrafast photoinduced processes such as charge transfer and spin crossover dynamics. This review presents an overview of the fundamental principles, experimental advances, and current theoretical approaches for interpreting M-edge spectra. We further discuss a range of applications in catalysis, materials science, and coordination chemistry, highlighting the technique’s growing impact and potential for future studies.« less

An indium–sulfide tetramer ([InMe 2 (SSiMe 3 )] 4 ), which contains reactive silyl and methyl groups, is shown to be an isolable intermediate in cluster synthesis. The reactive groups allow it to act as a synthon in the formation of multinuclear indium–sulfide architectures, evidenced by the crystallization of a coordination polymer ([In 20 S 14 Me 32 (4,4’-bpy) 5 ·5CH 2 Cl 2 ] n ) utilizing In 10 S 7 clusters as nodes. The reaction between trimethylindium (InMe 3 ) and bis(trimethylsilyl)sulfide (S(SiMe 3 ) 2 ) is explored with and without the presence of a ligating bipyridine.more » In both cases, a sulfide-indium adduct is formed, which slowly converts into a multimetallic complex. The ligand 2,2’-bipyridine (2,2’-bpy) is coordinated to InMe 3 to form the adduct InMe 3 (bpy), which upon addition of sulfide, eliminates tetramethylsilane (TMS) and binds two additional InMe 3 moieties (InMe 2 (bpy)(μ 3 -SSiMe 3 )(InMe 3 ) 2 ). When reacted neatly without bipyridine, InMe 3 and S(SiMe 3 ) 2 form the adduct InMe 3 (S(SiMe 3 ) 2 ), which subsequently eliminates TMS and intermolecularly associates to yield [InMe 2 (SSiMe 3 )] 4 . Although stable in an inert atmosphere, [InMe 2 (SSiMe 3 )] 4 undergoes facile hydrolysis to yield [InMeS] n when exposed to air. The effect of ligand addition (4,4’-bipyridine (4,4’-bpy)) to [InMe 2 (SSiMe 3 )] 4 is then examined. In every case, it is shown that the presence of the bpy ligand has a profound influence on the resulting structure, as shown by the unexpected formation of a trimer and In 10 S 7 cluster network.« less

Selective ethylene oligomerization via oxidative cyclization, forming metalacyclic intermediates, is typically catalyzed by molecular titanium and chromium complexes to produce butenes, hexenes, or octenes, depending on the supporting ligand framework. However, this mechanism requires significant electron density at the metal active site and is not known to be generalizable to other first-row transition metals. Here, we computationally investigate the electronic modulation of five transition metals (Mn, Fe, Co, Ni, and Cu) supported on titania (TiO₂) through reductive lithium intercalation to promote selective oligomerization via oxidative cyclization, using density functional theory (DFT). Our findings predict that Mn/LiTiO₂ exhibits high catalytic activitymore » due to the exergonic nature of oxidative cyclization with two ethylene molecules. Additionally, lithium titanate (LiTiO₂) supports enhance catalytic performance compared to TiO₂. Experimental validation confirms that Mn/LiTiO₂ achieves higher conversion rates and improved selectivity towards hexene (C₄:C₆ = 1:2.6). The enhanced activity is attributed to lithiation, which alters the electronic environment around Mn active sites. Mechanistic studies reveal that the formation of a seven-membered ring, a key intermediate for hexene formation, is more favorable on LiTiO₂ than TiO₂. This work provides the first evidence of Mn catalyzing selective ethylene oligomerization via oxidative cyclization in either homogeneous or heterogeneous catalysis.« less

Modeling multimetallic systems efficiently enables faster prediction of desirable chemical properties and the design of new materials. This work describes an initial implementation for performing multireference wave function method localized active-space self-consistent field (LASSCF) calculations through the use of multiple graphics processing units (GPUs) to accelerate time-to-solution. Density fitting is leveraged to reduce memory requirements, and we demonstrate the ability to fully utilize multi-GPU compute nodes. Performance improvements of 5–10x in total application runtime were observed in LASSCF calculations for multimetallic catalyst systems up to 1200 AOs and an active space of (22e,40o) using up to four NVIDIA A100 GPUs.more » Furthermore, written with performance portability in mind, a comparable performance is also observed in early runs on the Aurora exascale system using Intel Max Series GPUs.« less