Mesoporous Host Research Articles

Enhanced Cycling Stability of All-Solid-State Lithium-Sulfur Battery through Nonconductive Polar Hosts.

All-solid-state lithium-sulfur batteries (ASSLSBs) are promising next-generation battery technologies with a high energy density and excellent safety. Because of the insulating nature of sulfur/Li2S, conventional cathode designs focus on developing porous hosts with high electronic conductivities such as porous carbon. However, carbon hosts boost the decomposition of sulfide electrolytes and suffer from sulfur detachment due to their weak bonding with sulfur/Li2S, resulting in capacity decays. Herein, we propose a counterintuitive design concept of host materials in which nonconductive polar mesoporous hosts can enhance the cycling life of ASSLSBs through mitigating the decomposition of adjacent electrolytes and bonding sulfur/Li2S steadily to avoid detachment. By using a mesoporous SiO2 host filled with 70 wt % sulfur as the cathode, we demonstrate steady cycling in ASSLSBs with a capacity reversibility of 95.1% in the initial cycle and a discharge capacity of 1446 mAh/g after 500 cycles at C/5 based on the mass of sulfur.

Defect engineering enables an advanced separator modification for high-performance lithium-sulfur batteries

High-energy–density lithium-sulfur batteries have been rated as a promising, yet challenging, next-generation battery technology. Typically, the serious shuttle of polysulfide intermediates and sluggish solid–solid reaction kinetics often result in irreversibly sulfur loss, low Coulombic efficiency, and limited lifespan. Herein, we propose a facile and efficient separator modification strategy using a rationally designed sulfiphilic and lithiophilic mediator, i.e. in-situ confinement growth of oxygen-deficient TiO2-x nanoparticles within nitrogen-doped mesoporous carbon matrix to modulate the sulfur electrochemistry. The nanoscale defective catalyst within open mesoporous host affords favorable adsorption of polysulfides and catalytic conversion ability. Moreover, the versatile composite improves the electrolyte wettability and Li+ transfer kinetics and alleviates self-discharge behavior. Resultantly, the Li-S batteries using modified separator achieves significantly improved cycling stability with a low capacity decay of only 0.067% per cycle after 500 cycles at 2C. The defect engineering together with separator modification strategies enable efficient and durable Li-S batteries.

Insights into the aspect ratio effects of ordered mesoporous carbon on the electrochemical performance of sulfur cathode in lithium-sulfur batteries

Tailoring porous host materials, as an effective strategy for storing sulfur and restraining the shuttling of soluble polysulfides in electrolyte, is crucial in the design of high-performance lithium-sulfur (Li-S) batteries. However, for the widely studied conductive hosts such as mesoporous carbon, how the aspect ratio affects the confining ability to polysulfides, ion diffusion as well as the performances of Li-S batteries has been rarely studied. Herein, ordered mesoporous carbon (OMC) is chosen as a proof-of-concept prototype of sulfur host, and its aspect ratio is tuned from over ∼ 2 down to below ∼ 1.2 by using ordered mesoporous silica hard templates with variable length/width scales. The correlation between the aspect ratio of OMCs and the electrochemical performances of the corresponding sulfur-carbon cathodes are systematically studied with combined electrochemical measurements and microscopic characterizations. Moreover, the evolution of sulfur species in OMCs at different discharge states is scrutinized by small-angle X-ray scattering. This study gives insight into the aspect ratio effects of mesoporous host on battery performances of sulfur cathodes, providing guidelines for designing porous host materials for high-energy sulfur cathodes.

Preparation and characterization of biomimetic heterogeneous catalysts with Cu(II) and Mn(III) complexes

New catalysts were synthesized by immobilization of Cu(II) and Mn(III) biomimetic complexes onto mesoporous SBA-15 silica, amino-functionalized SBA-15, montmorillonite and Al-pillared montmorillonite supports. [Cu(acac)(phen)(OH2)](ClO4) and [Cu(acac)(Me2bipy)](ClO4) copper complexes and [Mn(III)(valen)(H2O)(CH3CN)](ClO4)∙CH3CN manganese complex supported on silica pore surface or intercalated into the interlayer spaces of clays, were characterized by X-ray diffraction, N2 adsorption-desorption, TGA-DTA analysis, IR and UV-Vis spectroscopy. These results have confirmed the structural stability of the mesoporous hosts and successful anchoring of the metal complexes over the supports. In order to verify the biomimetic comportment, catalytic activities of the free and immobilized complexes and that of Trametes versicolor laccase, immobilized on the same supports, were tested by oxidation with air of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), the most used substrate for estimation of specific activity of laccases. The supported complexes were more active than the free ones. Furthermore, the stability tests for the most active heterogeneous catalyst confirmed that the best support was NH2-SBA-15.

Innovative Investigation of Ordered Mesoporous Carbon Modified Separator for High Performance Lithium-Sulfur Batteries

These days, many portable electronic devices are used widely, and it makes secondary batteries important for future innovation. Li-ion battery which is most commonly used has the high specific energy and long cycle life. But it has problems with high price and possibility of explosion. Also it reaches the limitations of energy density for electric vehicles (EVs) and energy storage systems (ESS). Lithium-Sulfur battery is becoming a one of the promising alternatives. It has high theoretical capacity (1,675 mAh g-1) and specific energy density (~2600 Wh kg-1) and low cost. Also it is eco-friendly and safe. However, there is the primary problem to be commercialized. That one is called shuttle effect, which means dissolution of polysulfide into the electrolyte in the repetitive charging and discharging. It makes capacity decrease and internal resistance increase. And the active material and the discharge products, which are sulfur and Li2S2, Li2S, have low conductivity. The irreversible volume expansion during electrochemical reaction reaches to 80%. [1,2] To alleviate these problems, various sulfur host materials and modified separators have been investigated. [3,4] One of the representative approach is to apply carbon materials as sulfur hosts. Sulfur must be dispersed throughout the carbon conductor because of its low intrinsic electrical conductivity. The carbon matrix functions as a network for rapid electron transport. Various carbon materials, such as porous carbons, carbon nanotubes, or carbon materials with heteroatoms or chemical groups such as N, O, and S, have been employed to minimize polysulfide migration. One of the most effective sulfur hosts for limiting polysulfide diffusion is mesoporous carbon. By virtue of their inherent porosity and conductive carbon architecture, mesoporous carbon hosts have demonstrated better cycling performance. Another method for dealing with the shuttle effect is to form an interlayer between the cathode and the separator. Because the separator is an important role in battery safety and electrochemical performance, designing a high quality separator is critical for the development of high performance Li-S batteries. Separators made of polypropylene (PP) or polyethylene (PE) are commercially used and have some physical and electrochemical advantages. However, these separators have drawbacks such as low ionic conductivity and poor electrolyte compatibility. Various materials have been studied and used for modifying materials on the separator. For example, carbon materials, graphene oxides, and metal-organic frameworks are excellent at suppressing the shuttle effect of polysulfide. On the other hand, characterizing these structures and comprehending polysulfide behavior in these systems during electrochemical reaction, remain substantial challenges. Herein, we report on a dual-functional modified separator by applying ordered mesoporous carbon (OMC) on a commercial separator.The mesopores and the micropores of the OMC own a specific physical adsorption capability for polysulfide, thus it can adsorb a large amount of polysulfide. In addition, it is thermally and chemically stable. Also, the OMC can be detected by operando small-angle scattering (SAXS). In recent years, SAXS approach was applied to explain the ordered porous structure of sulfur host materials for Li-S batteries. These research provide information on how sulfur is adsorbed by porous carbon. This analysis identifies the changes of sulfur species as to whether polysulfide is adsorbed in mesopores or solid discharge products are formed on the surface, or infiltrated into micropores. The use of in-depth characterization techniques allows for more precise and independent assessment of the rapid electrochemical reactions in Li-S batteries. In brief, the highly ordered mesoporous carbon was synthesized, and it was used as an interlayer that served not only as a physical barrier to limit the polysulfide shuttle phenomena but also as an additional current collector to reuse active materials. By promoting the electrochemical reaction of active materials, it exhibited better electrochemical performance such as high capacity, stable cycle performance, and improved rate performance. The adsorbed polysufide and the behavior of sulfur species in the OMC during cycling were investigated using operando SAXS to acquire insight into the role of the OMC modified separator.[1] Li, Z.; He, Q.; Xu, X.; Zhao, Y.; Liu, X.; Zhou, C.; Ai, D.; Xia, L.; Mai, L. Adv. Mater. 2018, 30 (45), 1804089.[2] Zeng, L.-C.; Li, W.-H.; Jiang, Y.; Yu, Y. Rare Met. 2017, 36 (5), 339-364.[3] Liu, Z.; Liu, B.; Guo, P.; Shang, X.; Lv, M.; Liu, D.; He, D. Electrochim. Acta 2018, 269, 180-187.[4] Schuster, J.; He, G.; Mandlmeier, B.; Yim, T.; Lee, K. T.; Bein, T.; Nazar, L. F. Angew. Chem. 2012, 124 (15), 3651-3655. Figure 1

Investigating the impact of mesoporous and microporous carbon host materials on the performance of sulfur cathodes in Zinc-Sulfur batteries

The zinc-sulfur (Zn-S) batteries have attracted extensive research due to its high energy density and safety. However, numerous research focus has focused on optimizing the aqueous electrolyte, the effect of different confinement effects of carbon pores on sulfur on batteries is unclear. In this work, the effects of mesoporous and microporous hosts on electrochemical performance were investigated in detail. The microporous carbon structure provides higher confinement ability for sulfur compared to mesoporous carbon. Ex-situ XRD, EDS mapping, and XPS Ar ion etching techniques were utilized to analyze the factors contributing to the capacity decay of sulfur cathode materials. The insights gained from this study will not only enhance our understanding of the electrochemical behavior of Zn-S batteries, but also provide potential strategies for improving their performance.

Modulation of Fermi level gap and internal electric field over Cs3Bi2Br9@VO-In2O3 S-scheme heterojunction for boosted charge separation and CO2 photoconversion

Modulating the internal electric field (IEF) represents a potential strategy to stimulate the photocatalytic activity of heterojunctions, especially S-scheme photocatalysts. Herein, a Cs3Bi2Br9@VO-In2O3 (CBB@VO-In2O3) S-scheme heterojunction, of which Cs3Bi2Br9 perovskite quantum dots (PQDs) are embedded into mesoporous VO-In2O3 hosts, is rationally designed as a cornerstone for further IEF manipulation. Briefly, by introducing oxygen vacancies (VO) into the composed reduction semiconductor (mesoporous In2O3), an enlarged Fermi level (EF) gap between CBB and VO-In2O3 is achieved, yielding an intensified IEF over the CBB@VO-In2O3 heterojunction. Such an enhanced IEF affords a much more robust driving force for directional carrier delivery, leading to accelerated carrier transfer of CBB@VO-In2O3 heterojunction. Consequently, the optimized CBB@VO-In2O3 heterojunction features desirable CO2-to-CO conversion efficiency, and its CO production rate reaches 130.96 μmol g−1 h−1. The reaction intermediates and CO2 photoconversion pathway were unraveled by in-situ diffuse reflectance infrared Fourier transform spectroscopy. Combining with the DFT calculation, it was revealed that oxygen vacancies in VO-In2O3 act as reactive centers, which optimize the coordination modes of the intermediates, thus reducing the activation energy for photocatalytic CO2 reduction. Our work demonstrates that the IEF modulation of S-scheme-based heterojunction could significantly boost the charge separation and then to drive efficient catalytic reaction, achieving high-efficiency solar fuel production.

Nanostructurally Engineering Covalent Organic Frameworks for Boosting CO2 Photoreduction.

Herein, a series of imine-linked covalent organic frameworks (COFs) are developed with advanced ordered mesoporous hollow spherical nanomorphology and ultra-large mesopores (4.6nm in size), named OMHS-COF-M (M = H, Co, and Ni). The ordered mesoporous hollow spherical nanomorphology is revealed to be formed via an Ostwald ripening mechanism based on a one-step self-templated strategy. Encouraged by its unique structural features and outstanding photoelectrical property, the OMHS-COF-Co material is applied as the photocatalyst for CO2-to-CO reduction. Remarkably, it delivers an impressive CO production rate as high as 15 874µmol g-1 h-1, a large selectivity of 92.4%, and a preeminent cycling stability. From in/ex situ experiments and density functional theory (DFT) calculations, the excellent CO2 photoreduction performance is ascribed to the desirable cooperation of unique ordered mesoporous hollow spherical host and abundant isolated Co active sites, enhancing CO2 activation, and improving electron transfer kinetics as well as reducing the energy barriers for intermediates *COOH generation and CO desorption.

Nontraditional Approaches To Enable High-Energy and Long-Life Lithium-Sulfur Batteries.

ConspectusLithium-sulfur (Li-S) batteries are promising for automotive applications due to their high theoretical energy density (2600 Wh/kg). In addition, the natural abundance of sulfur could mitigate the global raw material supply chain challenge of commercial lithium-ion batteries that use critical elements, such as nickel and cobalt. However, due to persistent polysulfide shuttling and uncontrolled lithium dendrite growth, Li-S batteries using nonencapsulated sulfur cathodes and conventional ether-based electrolytes suffer from rapid cell degradation upon cycling. Despite significant improvements in recent decades, there is still a big gap between lab research and commercialization of the technology. To date, the reported cell energy densities and cycling life of practical Li-S pouch cells remain largely unsatisfactory.Traditional approaches to improving Li-S performance are primarily focused on confining polysulfides using electronically conductive hosts. However, these micro- and mesoporous hosts suffer from limited pore volume to accommodate high sulfur loading and the associated volume change during cycling. Moreover, they fail to balance adsorption-conversion of polysulfides during charge-discharge, leading to the formation of massive dead sulfur. Such hosts are themselves electrochemically inactive, which decreases the practical energy density. In contrast, a series of nontraditional approaches, paired with advances in multiscale mechanistic understanding, have recently demonstrated exciting performance outcomes not only in conventional coin cells but also in practical pouch cells.In this Account, we first introduce our novel cathode design strategies to overcome polysulfide shuttling and sluggish redox kinetics in thick S cathodes via selenium-sulfur chemistry and cathode host engineering. Next, we gain a mechanistic understanding of Li-S batteries in various types of electrolytes via a series of spectroscopic, nuclear magnetic resonance, and electrochemical methods. Meanwhile, a novel cathode solid electrolyte interphase encapsulation strategy via nonviscous highly fluorinated ether-based electrolyte is introduced. The established selection rule by investigating how solvating power retards the shuttle effect and induces robust cathode/solid-electrolyte interphase formation is also included. We then discuss how the synergistic interactions between rational cathode structures and electrolytes can be exploited to tailor the reaction pathways and kinetics of S cathodes under high mass loading and lean electrolyte conditions. In addition, a novel interlayer design to simultaneously overcome degradation processes (polysulfide shuttling and lithium dendrite formation) and accelerate redox reaction kinetics is presented. Finally, this Account concludes with an overview of the challenges and strategies to develop Li-S pouch cells with high practical energy density, long cycle life, and fast-charging capability.

3D Lithiophilic CuZrAg Metallic Glass Based-Current Collector for High-Performance Lithium Metal Anode.

Lithium metal anodes face several challenges in practical applications, such as dendrite growth, poor cycle efficiency, and volume variation. 3D hosts with lithiophilic surfaces have emerged as a promising design strategy for anodes. In this study, inspiration from the intrinsic isotropy, chemical heterogeneity, and wide tunability of metallic glass (MG) is drew to develop a 3D mesoporous host with a lithiophilic surface. The CuZrAgMG is prepared using the scalable melt-spinning technique and subsequently treated with a simple one-step chemical dealloying method. This resultes in the creation of a host with a homogeneously distributed abundance of lithium affinity sites on the surface. The excellent lithiophilic property and capability for uniform lithium deposition of the 3D CuZrAg electrode have been confirmed through theoretical calculations. Therefore, the 3D CuZrAg electrode displays excellent cyclic stability for over 400 cycles with 96% coulomb efficiency, and ultra-low overpotentials of 5mV for over 2000h at 1.0mAcm-2 and 1.0mAhcm-2 . Additionally, the full cells partied with either LiFePO4 or LiNi0.8 Co0.1 Mn0.1 O2 cathode deliver exceptional long-term cyclability and rate capability. This work demonstrates the great potential of metallic glass in lithium metal anode application.

Rationally Tailored Mesoporous Hosts for Optimal Protein Encapsulation.

Proteins play important roles in the therapeutic, medical diagnostic, and chemical catalysis industries. However, their potential is often limited by their fragile and dynamic nature outside cellular environments. The encapsulation of proteins in solid materials has been widely pursued as a route to enhance their stability and ease of handling. Nevertheless, the experimental investigation of protein interactions with rationally designed synthetic hosts still represents an area in need of improvement. In this work, we leveraged the tunability and crystallinity of metal-organic frameworks (MOFs) and developed a series of crystallographically defined protein hosts with varying chemical properties. Through systematic studies, we identified the dominating mechanisms for protein encapsulation and developed a host material with well-tailored properties to effectively encapsulate the protein ubiquitin. Specifically, in our mesoporous hosts, we found that ubiquitin encapsulation is thermodynamically favored. A more hydrophilic encapsulation environment with favorable electrostatic interactions induces enthalpically favored ubiquitin-MOF interactions, and a higher pH condition reduces the intraparticle diffusion barrier, both leading to a higher protein loading. Our findings provide a fundamental understanding of host-guest interactions between proteins and solid matrices and offer new insights to guide the design of future protein host materials to achieve optimal protein loading. The MOF modification technique used in this work also demonstrates a facile method to develop materials easily customizable for encapsulating proteins with different surface properties.

Space-Confined Guest Synthesis to Fabricate Sn-Monodispersed N-Doped Mesoporous Host toward Anode-Free Na Batteries.

Severe issues including volume change and dendrite growth on sodium metal anodes hinder the pursuit of applicable high-energy-density sodium metal batteries. Herein, an in situ reaction approach is developed that takes metal-organic frameworks as nano-reactor and pore-former to produce a mesoporous host comprised of nitrogen-doped carbon fibers embedded with monodispersed Sn clusters (SnNCNFs). The hybrid host shows outstanding sodiophilicity that enables rapid Na infusion and ultralow Na nucleation overpotential of 2mV. Its porous structure holds a high Na content and guides uniform Na deposition. Such host provides favorable Na plating/stripping with an average Coulombic efficiency of 99.96% over 2000 cycles (at 3mA cm-2 and 3mA h cm-2 ). The Na-infused SnNCNF anode delivers extreme Na utilization of 86% in symmetric cells (at 10mA cm-2 and 10mA h cm-2 ), outstanding rate capability and cycle life in Na-SnNCNF||Na3 V2 (PO4 )3 full cells (at 1 A g-1 for over 1000 cycles with capacity retention of 92.1%). Furthermore, high-energy/power-density anode-less and anode-free Na cells are achieved. This work presents an effective heteroatom-doping approach for fabricating multifunctional porous carbon materials and developing high-performance metal batteries.

Nanoarhitectonics of Inorganic-Organic Silica-Benzil Composites: Synthesis, Nanocrystal Morphology and Micro-Raman Analysis.

The synthesis of nanosized organic benzil (C6H5CO)2 crystals within the mesoporous SiO2 host matrix was investigated via X-ray diffraction, transmission electron microscopy, Raman spectroscopy, and ab initio lattice dynamics analysis. Combining these methods, we have proved that the main structural properties of benzil nanocrystals embedded into SiO2 host membranes with pore diameters of 6.0, 7.8, 9.4, and 13.0 nm are preserved compared to a bulk benzil crystal. Space confinement has an insignificant impact on the lattice vibrational properties of benzil crystals implanted into the host matrices. The ab initio lattice dynamics calculation of the phonon spectrum in the Brillouin zone center shows the mechanical and dynamical stability of benzil lattice, revealing very low optical frequency of 11 cm-1 at point Γ.

Direct and Indirect DNP NMR Uncovers the Interplay of Surfactants with Their Mesoporous Host Material

Two different mesoporous silica materials (SBA-15 and MCM 41) were impregnated with four different, commercially available surfactants, namely, E5, PEG 200, C10E6, and Triton X-100. Differential scanning calorimetry was employed to confirm the confinement of the surfactants in the pores of their host materials. Dynamic nuclear polarization enhanced solid state 13C magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra were recorded for these materials, showing that both the direct as well as the indirect polarization transfer pathways are active for the carbons of the polyethylene glycol moieties of the surfactants. The presence of the indirect polarization pathway implies the presence of molecular motion with correlation times faster than the inverse Larmor frequency of the observed signals. The intensities of the signals were determined, and an approach based on relative intensities was employed to ensure comparability throughout the samples. From these data, the interactions of the surfactants with the pore walls could be determined. Additionally, a model describing the surfactants’ arrangement in the pores was developed. It was concluded that all carbons of the hydrophilic surfactants, E5 and PEG 200, interact with the silica walls in a similar fashion, leading to similar polarization transfer pathway patterns for all observed signals. For the amphiphilic surfactants C10E6 and Triton X-100, the terminal hydroxyl group mediates the majority of the interactions with the pore walls and the polarizing agent.

Hybrid achromatic microlenses with high numerical apertures and focusing efficiencies across the visible

Compact visible wavelength achromats are essential for miniaturized and lightweight optics. However, fabrication of such achromats has proved to be exceptionally challenging. Here, using subsurface 3D printing inside mesoporous hosts we densely integrate aligned refractive and diffractive elements, forming thin high performance hybrid achromatic imaging micro-optics. Focusing efficiencies of 51–70% are achieved for 15μm thick, 90μm diameter, 0.3 numerical aperture microlenses. Chromatic focal length errors of less than 3% allow these microlenses to form high-quality images under broadband illumination (400–700 nm). Numerical apertures upwards of 0.47 are also achieved at the cost of some focusing efficiency, demonstrating the flexibility of this approach. Furthermore, larger area images are reconstructed from an array of hybrid achromatic microlenses, laying the groundwork for achromatic light-field imagers and displays. The presented approach precisely combines optical components within 3D space to achieve thin lens systems with high focusing efficiencies, high numerical apertures, and low chromatic focusing errors, providing a pathway towards achromatic micro-optical systems.

Fe(III) induced synthesis of mesoporous tannic acid-based host–guest complex and its favorable nature towards Congo red removal

Tannic acid-based composites are a crop of promising mussel-inspired adsorbents to remediate toxic contaminants in wastewater. This work innovatively fabricated tannic acid-based host–guest complex for Congo red (CR) removal from simulated solution, via Fe(III) refining the poly(tannic acid-1,6-hexamethylenediamine) (PTHA) resin. Highly dispersed Fe/PTHA complex was endowed larger superficial area (50.41 m2 g−1) and mesoporosity (23.39 nm) than pure PTHA due to the reinvented physical crosslinking framework accompanied by the conversion of Fe(III) to Fe(II). The microstructure and composition of Fe/PTHA composites were confirmed by TEM, SEM, EDS, BET, XPS etc. The adsorption behavior of Fe/PTHA-4 was well interpreted by the pseudo-second-order kinetic model and Langmuir model that established its saturated adsorption capacity of 588.24 mg g−1. Meanwhile, the process of CR uptake was spontaneous and endothermic, which presented a rate-limiting step, and the removal mechanism might be attributed to the effects of electrostatic attraction, hydrogen bond, π–π stack, and pore filling. These results suggest the reusable Fe/PTHA-4 host–guest composite is a promising candidate for the CR elimination in water body.

Enabling High Precision Gradient Index Control in Subsurface Multiphoton Lithography.

Multiphoton lithography inside a mesoporous host can create optical components with continuously tunable refractive indices in three-dimensional (3D) space. However, the process is very sensitive at exposure doses near the photoresist threshold, leading previous work to reliably achieve only a fraction of the available refractive index range for a given material system. Here, we present a method for greatly enhancing the uniformity of the subsurface micro-optics, increasing the reliable index range from 0.12 (in prior work) to 0.37 and decreasing the standard deviation (SD) at threshold from 0.13 to 0.0021. Three modifications to the previous method enable higher uniformity in all three spatial dimensions: (1) calibrating the planar write field of mirror galvanometers using a spatially varying optical transmission function which corrects for large-scale optical aberrations; (2) periodically relocating the piezoelectrically driven stage, termed piezo-galvo dithering, to reduce small-scale errors in writing; and (3) enforcing a constant time between each lateral cross section to reduce variation across all writing depths. With this new method, accurate fabrication of optics of any index between n = 1.20 and 1.57 (SD < 0.012 across the full range) was achieved inside a volume of porous silica. We demonstrate the importance of this increased accuracy and precision by fabricating and characterizing calibrated two-dimensional (2D) line gratings and flat gradient index lenses with significantly better performance than the corresponding control devices. As a visual representation, the University of Illinois logo made with 2D line gratings shows significant improvement in its color uniformity across its width.

Enhancing lithium storage performance of bimetallic oxides anode by synergistic effects

Spinel bimetallic transition metal oxide anode such as ZnMn2O4, has drawn increasing interest due to attractive bimetal interaction and high theoretical capacity. While it suffers from huge volume expansion and poor ionic/electronic conductivity. Nanosizing and carbon modification can alleviate these issues, while the optimal particle size within host is unclear yet. We here propose an in-situ confinement growth strategy to fabricate pomegranate-structured ZnMn2O4 nanocomposite with calculated optimal particle size in mesoporous carbon host. Theoretical calculations reveal favorable interatomic interactions between the metal atoms. By the synergistic effects of structural merits and bimetal interaction, the optimal ZnMn2O4 composite achieves greatly improved cycling stability (811 mAh g−1 at 0.2 A g−1 after 100 cycles), which can maintain its structural integrity upon cycling. X-ray absorption spectroscopy analysis further confirms delithiated Mn species (Mn2O3 but little MnO). Briefly, this strategy brings new opportunity to ZnMn2O4 anode, which could be adopted to other conversion/alloying-type electrodes.

Heterojunction interlocked catalysis-conduction network in monolithic porous-pipe scaffold for endurable Li-S batteries

The development of high-performance Li-S batteries is impeded by polysulfide (LiPS) shuttling effect and slow conversion kinetics. Building durable catalyst systems with rational adsorption-catalysis-conduction configurations to alleviate these problems still remains a challenge. Herein, a novel heterojunction interlocked catalysis-conduction strategy is proposed to prepare monolithic porous-pipe scaffold for LiPS accommodation. Therein the Co terminal of Co/Mo2C heterostructure catalyzes the in-situ growth of carbon nanotubes (CNTs). The Co-bridging effect reinforces the charge transfer from CNT to the catalytic Mo2C terminal of Co/Mo2C and avoids the coarsening of heterostructure nanodomains with superior anchoring and dispersing abilities. This high tap-density electrocatalytic scaffold (Co/Mo2C@CNTs) without excessive carbon residue as separator modifier enables the excellent rate capability and long cycling stability of Li-S batteries even under the pouch cell configuration, high sulfur loading and decreased electrolyte amount. This work also provides a novel top-down method to prepare mesoporous host with built-in conductive network from simple compact precursor via C3N4 vapor modulation.

Development of a sample cell for Radio Frequency µSR studies of metal nanoparticle systems with surface-adsorbed reactants in mesoporous hosts

We have recently begun an investigation of paramagnetic (free-radical) final states formed on metal nanoparticles by muonium (Mu) reactivity with surface-adsorbed molecules. The nanoparticles are incorporated into mesoporous silica, facilitating specific reaction steps in the silica host that involve H-atom transfer reactions important to studies in heterogeneous catalysis. Radio frequency (RF) methods are an essential tool for characterising final state species in these systems, and a non-metallic sample cell is essential for the RF field to penetrate the sample. Unfortunately, several significant problems were encountered during initial experiments using a cell made from PEEK polymer, the most serious being a temporal instability in the signals likely due to reactant molecules adsorbing on the PEEK. This paper discusses the problems encountered using the PEEK cell, and then considers the development of a ceramic cell designed to give better reproducibility in the measurements. The success of this new cell is demonstrated both through off-line tests and by muon measurements, including a series of TF 2G Mu spin precession measurements verifying the temporal stability of the experimental setup. Finally, an RF cavity was fashioned, and RF measurements made for muons stopped in bare silica, with signals from both diamagnetic and paramagnetic muon states clearly seen.