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Fabrication of hierarchical Lewis acid Sn-BEA with tunable hydrophobicity for cellulosic sugar isomerization
Lewis acid Sn-BEA catalysts with tunable morphology and hydrophobicity were successfully synthesized by the recrystallization of post-synthetic Sn-BEA in the presence of ammonium fluoride (NH4F) and tetraethylammonium bromide (TEABr). Three-dimensionally ordered mesoporous imprinted (3DOm-i) and nanocrystalline Sn-BEA catalysts with hydrophobic surface were synthesized for the first time by the method. This recrystallization method includes the dissolution of crystalline zeolite BEA by fluoride ions and the rearrangement of different types of silanol defects in the presence of TEABr. The method allows the final products to simultaneously inherit the morphology of their parent Al-BEA zeolites, and significantly reduce silanol defects within the catalysts. The Sn-BEA catalysts synthesized from the recrystallization method show largely enhanced catalytic performance for both glucose isomerization and bulky lactose isomerization in different solvents, which is presumably due to the hydrophobic surface and improved molecular transport property in the hierarchical zeolites. The recrystallization approach is a facile and reliable strategy to improve the hydrophobicity of zeolite catalysts with tunable morphologies ranging from nanocrystals to hierarchical structures.
Computational modelling of the thermoelectric properties of p-type Zintl compound CaMg2Bi2
Not Available
Ab initio study of electron mean free paths and thermoelectric properties of lead telluride
Not Available
Nanoscale Protection Layers To Mitigate Degradation in High-Energy Electrochemical Energy Storage Systems
In the pursuit of energy storage devices with higher energy and power, new ion storage materials and high-voltage battery chemistries are of paramount importance. Yet, they invite—and often enhance—degradation mechanisms, which are reflected in capacity loss with charge/discharge cycling and sometimes in safety problems. Degradation mechanisms are often driven by fundamentals such as chemical and electrochemical reactions at electrode–electrolyte interfaces, volume expansion and stress associated with ion insertion and extraction, and profound inhomogeneity of electrochemical behavior. Although it is important to identify and understand these mechanisms at some reasonable level, it is even more critical to design strategies to mitigate these degradation pathways and to develop means to implement and validate the strategies. A growing set of research highlights the mitigation benefits achievable by forming thin protection layers (PLs) intentionally created as artificial interphase regions at the electrode–electrolyte interface. These advances highlight a promising—perhaps even generic—pathway for enabling higher-energy and higher-voltage battery configurations. In this Account, we summarize examples of such PLs that serve as mitigation strategies to avoid degradation in lithium metal anodes, conversion-type electrode materials, and alloy-type electrodes. Examples are chosen from a larger body of electrochemical degradation research carried out in Nanostructures for Electrical Energy Storage (NEES), our DOE Energy Frontier Research Center. Overall, we argue on the basis of experimental and theoretical evidence that PLs effectively stabilize the electrochemical interfaces to prevent parasitic chemical and electrochemical reactions and mitigate the structural, mechanical, and compositional degradation of the electrode materials at the electrode–electrolyte interfaces. The evidenced improvement in performance metrics is accomplished by (1) establishing a homogeneous interface for ion insertion and extraction, (2) providing mechanical constraints to maintain structural integrity and robust electronic and ionic conduction pathways, and (3) introducing spatial confinements on the electrode material matrix to alter the phase transformation (delaying the occurrence of the conversion reaction) upon Li insertion, which results in superior electrode performance, excellent capacity retention, and improved reversibility. Taken together, these examples portray a valuable role for thin protection layers synthesized over electrode surfaces, both for their benefit to cycle stability and for revealing insights into degradation and mitigation mechanisms. Furthermore, they underscore the impact of complex electrochemical behavior at nanoscale materials and nanostructure interfaces in modulating the behavior of energy storage devices at the mesoscale and macroscale.
Nanocellulose toward Advanced Energy Storage Devices: Structure and Electrochemistry
We report that cellulose is the most abundant biopolymer on Earth and has long been used as a sustainable building block of conventional paper. Note that nanocellulose accounts for nearly 40% of wood’s weight and can be extracted using well-developed methods. Due to its appealing mechanical and electrochemical properties, including high specific modulus (~100 GPa/(g/cm 3 )), excellent stability in most solvents, and stability over a wide electrochemical window, nanocellulose has been widely used as a separator, electrolyte, binder, and substrate material for energy storage. Additionally, nanocellulose-derived carbon materials have also drawn increasing scientific interest in sustainable energy storage due to their low-cost and raw-material abundance, high conductivity, and rational electrochemical performance. The inexpensive and environmentally friendly nature of nanocellulose and its derivatives as well as simple fabrication techniques make nanocellulose-based energy storage devices promising candidates for the future of “green” and renewable electronics. For nanocellulose-based energy storage, structure engineering and design play a vital role in achieving desired electrochemical properties and performances. Thus, it is important to identify suitable structure and design engineering strategies and to better understand their relationship. In this Account, we review recent developments in nanocellulose-based energy storage. Due to the limited space, we will mainly focus on structure design and engineering strategies in macrofiber, paper, and three-dimensional (3D) structured electrochemical energy storage (EES) devices and highlight progress made in our group. We first present the structure and properties of nanocellulose, with a particular discussion of nanocellulose from wood materials. We then go on to discuss studies on nanocellulose-based macrofiber, paper, and 3D wood- and other aerogel-based EES devices. Within this discussion, we highlight the use of natural nanocellulose as a flexible substrate for a macrofiber supercapacitor and an excellent electrolyte reservoir for a breathable textile lithium–oxygen battery. Paper batteries and supercapacitors using nanocellulose as a green dispersant, nanocellulose-based paper as a flexible substrate, and nanocellulose as separator and electrolyte are also examined. We highlight recent progress on wood-based batteries and supercapacitors, focusing on the advantages of wood materials for energy storage, the structure design and engineering strategies, and their microstructure and electrochemical properties. We discuss the influence of structure (particularly pores) on the electrochemical performance of the energy storage devices. By taking advantage of the straight, nature-made channels in wood materials, ultrathick, highly loaded, and low-tortuosity energy storage devices are demonstrated. Lastly, we offer concluding remarks on the challenges and directions of future research in the field of nanocellulose-based energy storage devices.
(-)ESI/CAD MS n Procedure for Sequencing Lignin Oligomers Based on a Study of Synthetic Model Compounds with β-O-4 and 5-5 Linkages
Here, seven synthesized G-lignin oligomer model compounds (ranging in size from dimers to an octamer) with 5-5 and/or β-O-4 linkages, and three synthesized S-lignin model compounds (a dimer, trimer, and tetramer) with β-O-4 linkages, were evaporated and deprotonated using negative-ion mode ESI in a linear quadrupole ion trap/Fourier transform ion cyclotron resonance mass spectrometer. The collision-activated dissociation (CAD) fragmentation patterns (obtained in MS 2 and MS 3 experiments, respectively) for the negative ions were studied to develop a procedure for sequencing unknown lignin oligomers. On the basis of the observed fragmentation patterns, the measured elemental compositions of the most abundant fragment ions, and quantum chemical calculations, the most important reaction pathways and likely mechanisms were delineated. Many of these reactions occur via charge-remote fragmentation mechanisms. Deprotonated compounds with only β-O-4 linkages, or both 5-5 and β-O-4 linkages, showed major 1,2-eliminations of neutral compounds containing one, two, or three aromatic rings. The most likely mechanisms for these reactions are charge-remote Maccoll and retro-ene eliminations resulting in the cleavage of a β-O-4 linkage. Finally, facile losses of H 2 O and CH 2 O were also observed for all deprotonated model compounds, which involve a previously published charge-driven mechanism. Characteristic “ion groups” and “key ions” were identified that, when combined with their CAD products (MS 3 experiments), can be used to sequence unknown oligomers.
Chemoresponsive Nanofluidic Pump That Turns Off in the Presence of Lead Ion
There are many applications that require the integration of a pump and a chemical sensor so that the solution being pumped can be analyzed in real time for a specific chemical species and the flow adjusted according to the measured concentration of that species. In this paper, we describe an alternative strategy: a chemoresponsive pump where a single device acts as both the sensor and pump simultaneously. We demonstrate this concept with a nanofluidic Pb 2+ -responsive pump that uses electroosmotic flow as the pumping technology, and a Pb 2+ -binding ionophore that allows the device to selectively respond to Pb 2+ . The pump yields high flow rates at low Pb 2+ concentrations (<1 μM), but flow rate decreases with concentrations above this threshold and ultimately goes to zero at concentrations above 100 μM.
Structural Relationships and Absorption Spectroscopy of β-[NH 4 ][UF 5 ] and [NH 4 ][Pu 3 F 13 ]
Not provided.
Solvent-Engineering Method to Deposit Compact Bismuth-Based Thin Films: Mechanism and Application to Photovoltaics
Bismuth-based materials have been studied as alternatives to lead-based perovskite materials for photovoltaic applications. However, poor film quality has limited device performance. Here, we developed a solvent-engineering method and show that it is applicable to several bismuth-based compounds. Through this method, we obtained compact films of methylammonium bismuth iodide (MBI), cesium bismuth iodide (CBI), and formamidinium bismuth iodide (FBI). On the basis of film growth theory and experimental analyses, we propose a possible mechanism of film formation. Additionally, we demonstrate that the resultant compact MBI film is more suitable to fabricate efficient and stable photovoltaic devices compared to baseline MBI films with pinholes. We further employed a new hole-transporting material to reduce the valence-band offset with the MBI. The best-performing photovoltaic device exhibits an open-circuit voltage of 0.85 V, fill factor of 73%, and a power conversion efficiency of 0.71%, the highest reported values for MBI-based photovoltaic devices.
Impact of Size Dispersity, Ligand Coverage, and Ligand Length on the Structure of PbS Nanocrystal Superlattices
Understanding self-assembly is a critical step toward controlling structure at the nanometer length scale. Furthermore, small changes in nanoscale morphology can have large impacts on the performance of nanomaterial devices. In this work, we experimentally explore how the physical properties of lead sulfide (PbS) nanocrystals, such as the surface ligands and core size dispersity, affect the ability of these nanocrystals to self-assemble. Here, we quantified the self-assembly quality by monitoring grain size and the percentage of nanocrystals with coherent alignment of their atomic planes. We found that the ensemble size dispersity plays a large role in superlattice formation and that even small improvements in size distribution led to shorter neighbor-to-neighbor distances in superlattices (more efficient packing), larger grain sizes, and increased nanocrystal alignment. Additionally, the ligand coverage on nanocrystal surfaces had a significant influence on the self-assembly, and excess precipitation steps were highly detrimental to the formation of ordered solids. We show that surface ligand length is a more flexible parameter and that high-quality superlattices can still be achieved with compact surface ligands, so long as the nanocrystal size dispersity and ligand coverage are sufficient. Lastly, we investigated several different colloidal solvents, finding toluene to provide the best ordering, and show that nanocrystal self-assembly is largely unhindered by nanocrystal age. Overall, these results guide our understanding of the underlying factors influencing nanocrystal self-assembly and provide strategies for forming well-engineered superlattices.
Formation Mechanisms and Defect Engineering of Imine-Based Porous Organic Cages
The syntheses of porous organic cages (POCs) represent an important synthetic puzzle in dynamic covalent chemistry based self-sorting. Improved understanding of the formation mechanisms of POCs can lead to control and rational design of cages with desired functionality. Herein, we explore the formation mechanisms of imine-based POCs using time-resolved electrospray mass spectrometry, and electronic structure calculations at the density functional theory and correlated molecular orbital theory levels. We find that the synthesis of the [4+6] cycloimine cage CC3-R and the [2+3] cycloimine cage CC-pentane both proceed through similar intermediates via a series of consecutive reactions. The proposed reaction mechanisms are supported by electronic structure calculations. Based on our observations from both experiments and calculations, we propose a comprehensive method for designing and predicting new POC species. In addition, the observation of stable incomplete cages during CC3-R synthesis inspired us to design intentionally defective cages. These “missing-linker” type molecular defects are installed into CC3-R via non-solvent induced crystallization. The defective CC3-R materials are found to have enhanced CO2 interaction and improved CO 2 uptake capacity due to the additional functional groups present within the CC3 crystals.
U 8 Al 19 Si 6 , A Uranium Aluminide Silicide with a Stuffed Supercell Grown from Aluminum Flux
In this work, U 8 Al 19 Si 6 is formed from the reaction of uranium oxide and silicon in aluminum flux. Growth of this material is dependent on the presence of surface hydroxyl groups on alumina in the crucible. The compound forms as large cuboid crystals with a complex new structure that is a cubic stuffed supercell of UAl 3 (AuCu 3 parent structure type). It features a 4-fold expansion of the unit cell axis and the addition of atoms on two extra positions resulting in Pm$\bar{3n}$ symmetry. The ordered distribution of aluminum and silicon was determined using single crystal neutron diffraction. The magnetic susceptibility shows temperature independent paramagnetic behavior, while heat capacity measurements are consistent with Fermi liquid characteristics at low temperatures where the Sommerfeld constant is enhanced in comparison to that of a conventional metal. Lastly, these bulk thermodynamic properties indicate that U 8 Al 19 Si 6 is an itinerant electron Pauli paramagnet with moderately enhanced mass charge carrier quasiparticles.
Selective Transfer of Rotationally Commensurate MoS 2 from an Epitaxially Grown van der Waals Heterostructure
We report that large-scale synthesis of high-quality two-dimensional (2D) semiconductors is critical for their incorporation in emerging electronic and optoelectronic technologies. In particular, chemical vapor deposition (CVD) of transition-metal dichalcogenides (TMDs) via van der Waals epitaxy on epitaxial graphene (EG) leads to rotationally commensurate TMDs in contrast to randomly aligned TMDs grown on amorphous oxide substrates. However, the interlayer coupling between TMDs and EG hinders the investigation and utilization of the intrinsic electronic properties of the resulting TMDs, thus requiring their isolation from the EG growth substrate. To address this issue, we report here a technique for selectively transferring monolayer molybdenum disulfide (MoS 2 ) from CVD-grown MoS 2 -EG van der Waals heterojunctions using copper (Cu) adhesion layers. The choice of Cu as the adhesion layer is motivated by density functional theory calculations that predict the preferential binding of monolayer MoS 2 to Cu in contrast to graphene. Atomic force microscopy and optical spectroscopy confirm the large-scale transfer of rotationally commensurate MoS 2 onto SiO 2 /Si substrates without cracks, wrinkles, or residues. Furthermore, the transferred MoS 2 shows high performance in field-effect transistors with mobilities of up to 30 cm 2 /V s and on/off ratios of up to 10 6 at room temperature. Lastly, this transfer technique can likely be generalized to other TMDs and related 2D materials grown on EG, thus offering a broad range of benefits in nanoelectronic, optoelectronic, and photonic applications.
Tuning Anionic Chemistry To Improve Kinetics of Mg Intercalation
Rechargeable Mg batteries (RMBs) hold great promise for high energy density in consumer electronics because of the high theoretical volumetric capacity and dendrite-free stripping/plating of Mg. Their development, however, is severely limited by the sluggish diffusion of Mg 2+ in inorganic cathodes, mainly induced by strong interaction between Mg 2+ and host anions. In this paper, for the first time, we systematically investigate how anionic chemistry (O, S, and Se) affects Mg 2+ migration in layered MX 2 (M = Ti and V; X = O, S, and Se), by combining theoretical density functional theory (DFT) calculations with electrochemical characterizations. At room temperature, TiSe 2 and VSe 2 achieve much better electrochemical performance than TiS 2 and VS 2 , due to the faster migration of Mg 2+ in selenide than in sulfide and oxide, as demonstrated by electrochemical kinetic characterizations and DFT calculations. The improved kinetics of selenide can be attributed to three criteria: (i) larger diffusion channel, (ii) weaker interaction between Mg 2+ and anion lattice, and (iii) higher electronic conductivity. Finally, the three criteria might not only be applicable to layered materials but also be generalizable to materials with other structures, like Chevrel phase, spinel, olivine, etc., which paves the way for the future design and modification of intercalation materials for RMBs.
Role of Amine Structure on Hydrogen Sulfide Capture from Dilute Gas Streams Using Solid Adsorbents
The hydrogen sulfide composition in biogas ranges from 0 to 5% depending on the feed source to the biogas digester. To meet renewable natural gas specifications of 0–4 ppm of H 2 S content, technologies that remove H 2 S from raw biogas feeds are needed. This contribution assesses three adsorbents with similar textural and physical properties but with different amines grafted to the surface. Specifically, materials containing primary, secondary, and tertiary amines at the end of a propyl surface linker grafted on a silica support are explored. H 2 S adsorption isotherms and cyclic studies are presented for these materials, and it is shown that secondary amines have the best amine efficiency while tertiary amines are the most stable for H 2 S capture, of the materials studied. The results suggest the consideration of secondary and tertiary amines for the design of amine adsorbents suitable for H 2 S removal in dilute gas streams over multiple cycles.
Exploring the Acid Gas Sorption Properties of Oxidatively Degraded Supported Amine Sorbents
Amine-supported mesoporous oxide materials have proven to be effective acid gas sorbents. While the primary application of these supported amine species has been CO 2 capture, they have also shown to be proficient at adsorbing other damaging flue gas impurities such as SO x and NO x . The precise nature of the amine (primary, secondary, or tertiary) is known to dictate the gas–amine interactions, with tertiary amines of particular interest due to their inability to adsorb dry CO 2 , favoring SO x and NO x species. The different amine sites also provoke differences in oxidative stability, when exposed to temperatures similar to those used for thermal desorption procedures. Herein we focus on the structural and chemical changes that occur in a range of class 1 (amine-impregnated) and class 2 (amine-grafted) sorbents upon oxidation and correlate these with their variation in acid gas (CO 2 , NO 2 , and SO 2 ) uptakes, as a function of the oxidation temperature. These studies suggest that oxidatively degraded or “spent” supported amine materials may have possible uses as NO x or SO x sorbents. Specifically, despite oxidative degradation these aminopolymer species maintain a reasonable level of NO 2 uptake, despite losing the ability to capture SO 2 or CO 2 , offering unique possibilities in selective NO 2 capture.