Chemical Confinement Research Articles

Coordinative Binding of Polymers to Metal-Organic Framework Nanoparticles for Control of Interactions at the Biointerface.

Metal-organic framework nanoparticles (MOF NPs) are of growing interest in diagnostic and therapeutic applications, and due to their hybrid nature, they display enhanced properties compared to more established nanomaterials. The effective application of MOF NPs, however, is often hampered by limited control of their surface chemistry and understanding of their interactions at the biointerface. Using a surface coating approach, we found that coordinative polymer binding to Zr- fum NPs is a convenient way for peripheral surface functionalization. Different polymers with biomedical relevance were assessed for the ability to bind to the MOF surface. Carboxylic acid and amine containing polymers turned out to be potent surface coatings and a modulator replacement reaction was identified as the underlying mechanism. The strong binding of polycarboxylates was then used to shield the MOF surface with a double amphiphilic polyglutamate-polysarcosine block copolymer, which resulted in an exceptional high colloidal stability of the nanoparticles. The effect of polymer coating on interactions at the biointerface was tested with regard to cellular association and protein binding, which has, to the best of our knowledge, never been discussed in literature for functionalized MOF NPs. We conclude that the applied approach enables a high degree of chemical surface confinement, which could be used as a universal strategy for MOF NP functionalization. In this way, the physicochemical properties of MOF NPs could be tuned, which allows for control over their behavior in biological systems.

A high-entropy metal oxide as chemical anchor of polysulfide for lithium-sulfur batteries

Lithium-sulfur (Li-S) battery is anticipated as one of the most promising candidates for the next-generation rechargeable cell. In order to conquer the shuttle effect of dissolution lithium polysulfides (LIPSs), the chemical interactions between sulfur host and LIPSs on the performance of Li-S batteries has recently been highlighted. Herein, a facile strategy is proposed, which produces a high-entropy metal oxide (HEMO-1) as an anchor to restrain LIPSs in Li-S batteries via chemical confinement as demonstrated by strong bonding interaction between HEMO-1 and Li2S6. The as-prepared HEMO-1 incorporates five metal components, Ni, Mg, Cu, Zn and Co, into a metal oxide crystalline structure. The homogeneously dispersive multiple metal active species in HEMO-1 favor the restriction of LIPSs and facilitate the redox reaction in the cathode of Li-S batteries. Especially, the synergistic contribution of Li-O and S-Ni bonds from the interaction between HEMO-1 and LIPSs effectively alleviate the shuttle of LIPSs between the cathode and anode. As the promoter catalyst for LIPSs, HEMO-1 shows a competitive reversible capacity, outstanding cycling stability, and a low capacity decay of 0.077% per cycle after 600 cycles. This study not only presents a high-entropy oxide promoter for polysulfide immobilizing in Li-S batteries, but also provides an avenue of high-entropy metal oxides to a variety of energy conversion and storage fields.

Uniform Mesoporous MnO2 Nanospheres as a Surface Chemical Adsorption and Physical Confinement Polysulfide Mediator for Lithium-Sulfur Batteries.

The actual implementation of lithium-sulfur batteries is hindered by inferior cyclic stability and poor coulombic efficiency stemming from the notorious shuttling of soluble polysulfide intermediates. Herein, uniform mesoporous MnO2 nanospheres were prepared using a facile self-assembly and room-temperature reaction method. As a sulfur carrier of sulfur cathodes, the versatile architecture of MnO2 not only provides powerful chemical adsorption to anchor polysulfide intermediates on the large polar surface area but also restrains them within the nanopores by physical confinement. The mesoporous MnO2-stabilized sulfur cathode demonstrates a high initial reversible capacity of 1349.3 mA h g-1 and a capacity fading rate of 0.073% at 1.0 C over 500 cycles. Furthermore, a reversible areal capacity of 2.5 mA h cm-2 was achieved with stable cycling performance at a sulfur content of 80.7%. Our work offers a facile method to build efficient sulfur cathodes for high performance lithium-sulfur batteries.

Nano sulfur particles decorated bi-lamella composites for superior electromagnetic wave absorption

Sulfur nanoparticles decorated bi-lamella composites with multiple interfaces were constructed by introducing a handful of nano-S particles into the interlayer of graphene and poly (3,4-ethylene-dioxythiophene): poly (styrenesulfonate) (GSP). Graphene and PEDOT: PSS with large surface areas and abundant functional groups offer adequate contact sites for the chemical confinement of sulfur nanoparticles. Based on the equivalent circuit theory, insulating sulfur could commendably regulate hopping conduction by slowing down the hopping electrons among the layers. Meanwhile, the substantial conductivity differences result in evident interfacial polarization (MWS effect). With the favorable permittivity behavior and multiple interfacial polarizations, more microwaves could be brought into the interior of absorber and were consumed. The GSP-paraffin composites with 35 wt% GSP loading possess the minimum reflection loss (RL) value of −21.9 dB at 1.6 mm, and effective absorption bandwidth of 4.72 GHz. This work demonstrates the significant role of multi-interfaces on microwave absorption.

Squalene-derived sulfur-rich copolymer@ 3D graphene-carbon nanotube network cathode for high-performance lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries with high theoretical energy density and low cost are considered a promising energy storage system. However, great challenges still remain in achieving high sulfur loading and long cycle life. Herein we report a well-designed sulfur-rich copolymer@ 3D graphene-carbon nanotubes (G-CNT) network cathode for high-performance Li-S batteries. The sulfur-rich copolymer (87.29% sulfur) synthesised by inverse vulcanization between two eco-friendly sources, sulfur and squalene, can greatly suppress the dissolution of sulfur and polusulfides due to the chemical confinement from the crosslinking of polysulfur chains with the squalene molecules. The interlinked Sp2 G-CNT network can not only further enhance the polysulfide entrapment capability, but also provide the composite with an 3D electrical conductive path as well as an eminent mechanical resilience towards the huge volume change of sulfur. The as-developed cathode can deliver a high specific capacity of 1265 mAh g−1 at 0.2C with excellent rate performance and cycling stability (782 mAh g−1 at after 300 cycles at 1C).

Chemical anchoring of SeS2 on a fluoro-substituted covalent organic framework as a high-performance cathode material.

In this work, a high-performance cathode material was achieved by using SeS2 post-functionalization of a fluorinated covalent organic framework (COF) through SNAr chemistry. The chemical and physical confinement of polysulfides and polyselenides combined with enhanced conductivity boosted its electrochemical performance as a cathode material for lithium-sulfur batteries (LSBs). COF-F-SeS2 delivered a discharge capacity of 1633 mA h g-1 at 0.1C, an excellent C-rate performance of 1163 mA h g-1 at 1C and favorable long cycle performance. This work provides a feasible strategy to overcome the bottlenecks of LSBs for high capacity, excellent C-rate performance and enhanced cycle performance.

Improvement of Li-Sulfur Cell Cycling Performance by Use of Fe1-xS@NC as a Functional Additive for Chemical Confinement of Lithium Polysulfides

Lithium-sulfur cells using sulfur as an active cathode material offer high energy density and low-cost. However, dissolution and migration of lithium polysulfides (the ‘shuttle effect’) remain key obstacles for the practical development of lithium-sulfur cells. Here, we demonstrate that Fe1-xS (pyrrhotite) coated by N-doped carbon (Fe1-xS@NC) with high affinity for polysulfides and high electronic conductivity can be used as a functional additive to trap lithium polysulfides and reutilize reaction intermediates in the sulfur cathode during cycling. The addition of Fe1-xS@NC into the sulfur cathode results in the enhancement of cycling performance of the lithium-sulfur cell in terms of initial discharge capacity, capacity retention and rate capability. This superior cycling performance can be attributed to strong chemical interactions between electrically conductive Fe1-xS@NC particles and lithium polysulfides, which suppress the dissolution of lithium polysulfides and enhance the utilization of active sulfur during repeated cycling.

Highly Fluoro-Substituted Covalent Organic Framework and Its Application in Lithium-Sulfur Batteries.

We report the preparation of a highly fluoro-substituted crystalline covalent organic framework (COF) and its application as a cathode material in lithium-sulfur batteries (LSBs) upon sulfur confinement. A sulfur-functionalized COF with high sulfur content (60 wt %) was obtained through physisorption of elemental sulfur and subsequent SNAr reaction of sulfur with aromatic fluorides on the COF backbone. After such physical and chemical confinement of sulfur through a postfunctionalization approach, the COF material still shows some structural order, allowing us to investigate the structure-property relationship of such COF materials in LSB application. We compared the electrochemical performances of the two cathode materials prepared from a crystalline COF and its amorphous counterpart and studied the important factors that affect battery capacity, reaction kinetics, and cycling stability.

Robustly immobilized Ni2P nanoparticles in porous carbon networks promotes high-performance sodium-ion storage

Transition metal phosphides are promising anode materials for next-generation rechargeable sodium-ion batteries due to the high theoretical capacities. However, the inherent low conductivity and large volume expansion of transition metal phosphides during the repeated sodiation/desodiation process critically hinder their practical applications. Herein, we immobilize Ni2P nanoparticles robustly in porous carbon sheet networks via the pyrolysis and in-situ phosphatization of poly(acrylic acid)-Ni(NO3)2 gel. The resulted porous network structure, high conductivity, robust chemical combination and space confinement effect of the Ni2P-carbon composite offer the electrode not only rigid structural stability for volume expansion over long-term cycling, but also large specific capacity and fast Na+/electrons transfer kinetics. As a consequence, the composite delivers a large initial discharge capacity (932 mAh g−1 at 50 mA g−1), a high rate capability (77 mAh g−1 at 3500 mA g−1), as well as a significantly enhanced long cycle-life (146 mAh g−1 after 1500 cycles at 500 mA g−1). The excellent Na-storage performance makes the synthesized Ni2P-carbon composite a sound anode material for advanced rechargeable SIBs.

Controlled Synthesis of Sulfur-Rich Polymeric Selenium Sulfides as Promising Electrode Materials for Long-Life, High-Rate Lithium Metal Batteries.

High-energy lithium/sulfur (Li/S) batteries still suffer from unsatisfactory cycle life and poor rate capability caused by the polysulfides shuttle and insulating nature of S cathodes. Here, we report our findings in the controlled synthesis of selenium (Se)-containing S-rich co-polymers of various compositions as novel cathode materials through a facile inverse vulcanization of S with selenium disulfide (SeS2) and 1,3-diisopropenylbenzene (DIB) as co-monomers. Nuclear magnetic resonance and X-ray photoelectron spectroscopy results show that divinyl functional groups of DIB were chemically cross-linked with S/SeS2 chain radicals through a ring-opening polymerization. The newly formed bonds of C-S, C-Se, and S-Se in novel S-SeS2-DIB co-polymers effectively alleviate the shuttle effects of polysulfides/polyselenides. Furthermore, various electrochemical techniques confirm the positive roles of Se-containing co-polymers in enhancing the electrode reaction kinetics and the formation of stable solid electrolyte interphase layer with low charge-transfer resistance, leading to improved high-rate performances. The as-synthesized co-polymer was then infiltrated into well-interconnected, porous nanocarbon networks (Ketjenblack EC600JD, KB600) to provide effective paths for the fast electron transport. Due to the synergistic combination of chemical and physical confinement of the reaction intermediates during cycling, good reversibility for 500 cycles with a low decay rate of 0.0549% per cycle was achieved at 1000 mA g-1. These encouraging results suggest that the combination of chemical incorporation of SeS2 into S-rich co-polymer and the physical confinement of carbon networks is a promising strategy for advancing Li/S batteries and their viability for practical applications.

Fabrication of Fe2C Embedded in Hollow Carbon Spheres: a High‐Performance and Stable Catalyst for Fischer‐Tropsch Synthesis

AbstractThe Fischer−Tropsch synthesis (FTS) is a non‐petroleum‐based alternative route, which directly produces fuels and value‐added chemicals (e. g. lower olefins) from coal‐, biomass‐ or natural gas‐derived syngas. The ϵ‐iron carbide, such as Fe2C, has been predicted to be active but not stable under high‐temperature FTS conditions. In this work, we have fabricated a novel catalyst with Fe2C embedded in hollow carbon spheres (HCS) by pyrolyzing the coated polymer and Fe(NO3)3 on silica spheres and then etching the hard template. XRD, XPS, TEM and N2 physical adsorption were employed to characterize the evolution and properties of as‐prepared catalysts, which significantly depend on pyrolysis temperature. Under FTS conditions, the obtained catalysts exhibit good dispersion, robustness of geometric construction, and resistance to sintering. More importantly, Fe2C was confirmed as the dominant and stable iron carbide species. The unique chemical surrounding and confinement effect provided by carbon matrix contribute to these peculiarities that are responsible for superior activity and stability in FTS. Furthermore, we found that the products distribution could be manipulated by changing the geometric diameters of HCS, due to the tunable CO/H2 ratio.

Highly Reversible Li\u2013Se Batteries with Ultra-Lightweight N,S-Codoped Graphene Blocking Layer

The desire for practical utilization of rechargeable lithium batteries with high energy density has motivated attempts to develop new electrode materials and battery systems. Here, without additional binders we present a simple vacuum filtration method to synthesize nitrogen and sulfur codoped graphene (N,S-G) blocking layer, which is ultra-lightweight, conductive, and free standing. When the N,S-G membrane was inserted between the catholyte and separator, the lithium–selenium (Li–Se) batteries exhibited a high reversible discharge capacity of 330.7 mAh g−1 at 1 C (1 C = 675 mA g−1) after 500 cycles and high rate performance (over 310 mAh g−1 at 4 C) even at an active material loading as high as ~ 5 mg cm−2. This excellent performance can be ascribed to homogenous dispersion of the liquid active material in the electrode, good Li+-ion conductivity, fast electronic transport in the conductive graphene framework, and strong chemical confinement of polyselenides by nitrogen and sulfur atoms. More importantly, it is a promising strategy for enhancing the energy density of Li–Se batteries by using the catholyte with a lightweight heteroatom doping carbon matrix.

Graphene-Based Materials with Different Morphologies and Structures as Interlayers for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur batteries have recently attracted great attention as the promising candidates for next-generation energy storage devices due to its high theoretical capacity (~1675 mAh g-1), environmentally friendly, and natural abundance. However, the practical application of LSBs is still hindered by the shuttle of soluble lithium polysulfides (LPSs) and low conductivity of sulfur itself causing the poor electrochemical performance and poor cycling stability. In this work, graphene-based interlayers with different morphologies and structures were introduced to trap LPSs and reduce the shuttle effect. The LSB using 3D N-doped reduced graphene oxide aerogel interlayer exhibits the highest specific capacities of 1236.0, 1037.5, 979.7, 835.0, and 345.4 mAh g-1 at the applied current densities of 0.1, 0.2, 0.5, 1.0, and 2.0C, respectively which is higher than other graphene-related interlayers. The synergistic effect between N-doping and 3D frameworks can suppress the LPSs via both chemical adsorption interaction and physical confinement as well as increase the electrical conductivity of the entire electrode.

Nitrogen‐Doped Graphene‐Supported Mixed Transition‐Metal Oxide Porous Particles to Confine Polysulfides for Lithium–Sulfur Batteries

AbstractThe intricate charge–discharge reactions and bad conductivity nature of sulfur determine the extreme importance of cathode engineering for Li–S batteries. Herein, spinel ZnCo2O4 porous particles@N‐doped reduced graphene oxide (ZnCo2O4@N‐RGO) are prepared via the combined procedures of refluxing and hydrothermal treatment, consisting of interconnected uniform ZnCo2O4 nanocubes with an average size of 5 nm anchored on graphene nanosheets. The as‐obtained composite can act as an inimitable cathode scaffold to suppress the shuttling of polysulfides by chemical confinement of ZnCo2O4 and N‐RGO for the first time, as demonstrated by the adsorption energy of ZnCo2O4 to Li2S4 via the strong chemical bonding between Zn or Co and S. The RGO nanosheets with a relatively high specific surface area provide a good conductive network and structural stability. The introduction of doped N atoms and numerous ZnCo2O4 porous nanoparticles can inhibit the transfer of lithium polysulfides between the cathode and anode. Due to the unique structural and compositional features, the as‐obtained hybrid materials with the high sulfur loading of 71% and even 82% still deliver high specific capacity, good rate capability, and enhanced cycling stability with exceptionally high initial Coulombic efficiency, which displays a high utilization of sulfur.

Recent progress on confinement of polysulfides through physical and chemical methods

Abstract With high theoretical energy density and the natural abundance of S, lithium-sulfur (Li–S) batteries are considered to be the promising next generation high-energy rechargeable energy storage devices. However, issues including electronical insulation of S, the lithium polysulfides (LiPSs) dissolution and the short cycle lifespan have prevented Li–S batteries from being practical applied. Feasible settlements of confining LiPSs to reduce the loss of active substances and improve the cycle stability include wrapping sulfur with compact layers, designing matrix with porous or hollow structures, adding adsorbents owning strong interaction with sulfur and inserting polysulfide barriers between cathodes and separators. This review categorizes them into physical and chemical confinements according to the influencing mechanism. With further discussion of their merits and flaws, synergy of the physical and chemical confinement is believed to be the feasible avenue that can guide Li–S batteries to the practical application.

Vanadium Dioxide-Graphene Composite with Ultrafast Anchoring Behavior of Polysulfides for Lithium–Sulfur Batteries

The lithium-sulfur (Li-S) battery has been deemed as one of the most promising energy-storage systems owing to its high energy density, low cost, and environmental benignancy. However, the capacity decay and kinetic sluggishness stemming from polysulfide shuttle effects have by far posed a great challenge to practical performance. We herein demonstrate the employment of low-cost, wet-chemistry-derived VO2 nanobelts as the effective host additives for the graphene-based sulfur cathode. The VO2 nanobelts displayed an ultrafast anchoring behavior of polysulfides, managing to completely decolor the polysulfide solution in 50 s. Such a fast and strong anchoring ability of VO2 was further investigated and verified by experimental and theoretical investigations. Benefitting from the synergistic effect exerted by VO2 in terms of chemical confinement and catalytic conversion of polysulfides, the Li-S batteries incorporating VO2 and graphene manifested excellent cycling and rate performances. Notably, the batteries delivered an initial discharge capacity of 1405 mAh g-1 when cycling at 0.2 C, showed an advanced rate performance of ∼830 mAh g-1 at 2 C, and maintained a stable cycling performance at high current densities of 1, 2, and 5 C over 200 cycles, paving a practical route toward cost-effective and environmentally benign cathode design for high-energy Li-S batteries.

Porphyrin Organic Framework Hollow Spheres and Their Applications in Lithium-Sulfur Batteries.

Organic frameworks represent an emerging family of advanced materials that can be precisely controlled at the atomic level. However, morphology control of organic frameworks remains perplexing and difficult, strongly limiting the advantages of organic frameworks in multiple practical applications. Herein, porphyrin organic framework hollow spheres (POF-HSs) are fabricated by a template method as a proof of concept of organic frameworks with precisely controlled morphology. POF-HS exhibits explicit chemical structures of 2D POF and an expected hollow structure. The morphology of POF-HS is further regulated in terms of void size and shell thickness. Benefited from the polar chemical structures and the hollow spherical morphology, POF-HS sufficiently mitigates the shuttle of polysulfides by taking the dual effects of chemical adsorption and physical confinement and functions as a desirable host material for sulfur cathode to endow lithium-sulfur batteries with high capacity, long cycling life, and excellent rate performance. The accurate synthesis of POF-HSs demonstrates the highly controllable and versatile morphology of organic framework materials beyond precise integration of organic building blocks and represents infinite possibility of offering exotic organic frameworks for chemistry, sustainable energy, and material science.

Double-Nets Enclosed Sulfur Composite As a New Cathode in Lithium Sulfur Batteries

Most of efforts on physical confinements of lithium polysulfides to kinetically slow down the ‘shuttling effect’ in Li-S batteries have been tried to date. However, to avoid the thermodynamic loss of the sulfides, a stronger bonding particularly with a chemical bonding displays more effective way to mitigate the ‘flow away’ process. Here we created a double-nets matrix, which is composed of a low cost, mesoporous activated carbon (AC) and a covered nanoporous oxide cap. The oxide cap not only efficiently ‘blocks’ the sulfide molecular, but also chemically bonds the molecular that greatly delays the diffusion of the sulfide, thus leading to a high capacity retention. The initial capacity of 1600 mAh/g was achieved, which is close to the theoretical capacity. An excellent capacity retention with >900 mAh/g and >705 mAh/g were obtained after 500 cycles at 0.2 and 0.5 C, respectively. At a higher rate of 2.0 C, a capacity of as high as 470 mAh/g was still maintained after 500 cycles, which still keeps a capacity of >400 mAh/g after 1000 cycles with a Coulombic efficiency of 99.8%. Further, a wide range of sulfur ratio of the composite is from 47% up to 73%, enabling a high loading of active material up to >5.0 mg/cm2. This outstanding cycling performance is attributed to the double-nets physical and chemical confinements. The current high cycling and rate performance of the Li-S battery using industry available AC and sulfur provide a high potential in mass production for broad applications of potable electronic devices.

Hydration dynamics of a lipid membrane: Hydrogen bond networks and lipid-lipid associations

Dynamics of hydration layers of a dimyristoylphosphatidylcholine (DMPC) bilayer are investigated using an all atom molecular dynamics simulation. Based upon the geometric criteria, continuously residing interface water molecules which form hydrogen bonds solely among themselves and then concertedly hydrogen bonded to carbonyl, phosphate, and glycerol head groups of DMPC are identified. The interface water hydrogen bonded to lipids shows slower relaxation rates for translational and rotational dynamics compared to that of the bulk water and is found to follow sub-diffusive and non-diffusive behaviors, respectively. The mean square displacements and the reorientational auto-correlation functions are slowest for the interfacial waters hydrogen bonded to the carbonyl oxygen since these are buried deep in the hydrophobic core among all interfacial water studied. The intermittent hydrogen bond auto-correlation functions are calculated, which allows breaking and reformations of the hydrogen bonds. The auto-correlation functions for interfacial hydrogen bonded networks develop humps during a transition from cage-like motion to eventual power law behavior of t−3/2. The asymptotic t−3/2 behavior indicates translational diffusion dictated dynamics during hydrogen bond breaking and formation irrespective of the nature of the chemical confinement. Employing reactive flux correlation analysis, the forward rate constant of hydrogen bond breaking and formation is calculated which is used to obtain Gibbs energy of activation of the hydrogen bond breaking. The relaxation rates of the networks buried in the hydrophobic core are slower than the networks near the lipid-water interface which is again slower than bulk due to the higher Gibbs energy of activation. Since hydrogen bond breakage follows a translational diffusion dictated mechanism, chemically confined hydrogen bond networks need an activation energy to diffuse through water depleted hydrophobic environments. Our calculations reveal that the slow relaxation rates of interfacial waters in the vicinity of lipids are originated from the chemical confinement of concerted hydrogen bond networks. The analysis suggests that the networks in the hydration layer of membranes dynamically facilitate the water mediated lipid-lipid associations which can provide insights on the thermodynamic stability of soft interfaces relevant to biological systems in the future.

Highly crosslinked organosulfur copolymer nanosheets with abundant mesopores as cathode materials for efficient lithium-sulfur batteries

Low sulfur utilization and poor cycling stability are two major factors that currently impede the wide-spread commercialization of lithium-sulfur (Li-S) batteries. Herein, sulfur-rich side chains are anchored onto Schiff-base copolymer of thiourea aldehyde resin (cp (S-TAR)) nanosheets via inverse vulcanization to form a large number of intermolecular crosslinkers as well as mesopores. Application of the resultant copolymer as a cathode material in Li-S batteries can not only provide abundant porous channels for Li+ diffusion but also significantly alleviate the dissolution of polysulfides by chemical confinement through the covalent bonds between sulfur-rich side chains and TAR. With this novel polymer cathode, a Li-S battery prototype is constructed which can operate at 1 C for over 500 charge-discharge cycles at nearly 99% coulombic efficiency, showing an ultralow cyclic fading rate of 0.045% per cycle, and an outstanding high-rate response of up to 5 C. The present strategy demonstrates the great potential of using highly crosslinked organosulfur copolymers as high-performance polymer cathode materials for low-cost, high-energy density Li-S batteries.