Porous Host Research Articles

(Invited) High Surface Area N-Doped Carbon Fibers with Accessible Reaction Sites for All Solid State Lithium Sulfur Batteries

All solid-state lithium-sulfur batteries (ASSLSBs) are believed to deliver extremely higher energy density and remarkable safety than conventional Lithium-Sulfur batteries using liquid electrolytes. However, the low utilization of active material (sulfur) caused by sluggish reaction kinetics greatly hindered the development of ASSLSBs. It is significant to fabricate an advanced electrode where sulfur has efficient electron/ion accessibility. Porous carbon host, which has been widely used in liquid cells, is proposed to address the challenges. However, the conventional porous carbon host used in liquid cells can not be directly used in ASSLSBs, because the nonmobile solid electrolytes can not reach the sulfur confined in the pores buried deeply inside the carbon. An ideal porous carbon host should own a large specific surface area to provide sufficient sites for sulfur, but it is very critical that the pores should only locate at the out surface of the carbon. Till now, though many works reported the application of porous carbon in ASSLSBs, but none of them discussed the structure requirement of porous carbon. Here, for the first time, we discussed the ideal structure of the porous carbon and developed a polyacrylonitrile-derived porous carbon fibers (named PPCF) with a unique core-shell structure where a layer of micropores cover on dense core contributing to a high specific surface area.Porous carbon fibers were successfully prepared through electrospinning and following carbonization and activation processes. This PPCF owns a unique core-shell structure where a layer of micropores is covered on the dense cores. A high specific surface area of 1519 m2 g-1 was achieved, and the micropores could effectively confine the sulfur avoiding the formation of bulky sulfur. More importantly, the pores mainly distributed on the outer surface which rendered remarkable ion access to sulfur, contributing to high sulfur utilization. The fibrous morphology enabled efficient electron conduction paths through effective percolation. Compared with the vapor grown carbon fibers (VGCF), a common carbon fiber with no surface pores, the cathode using PPCF exhibited improved reaction kinetics with an overpotential reduction by 149 mV. The reduced overpotential explains the faster kinetic and higher utilization of sulfur in S-PPCF-SE. In the dQ/dV measurement, S-PPCF-SE showed strong anodic/cathodic peaks with high intensity of 3156/4367 mAh g-1 V-1 which are significantly higher than 1010/1268 mAh g-1 V-1 in S-VGCF-SE, demonstrating a greatly improved reaction kinetics. The ASSLSBs using PPCF exhibited three times enhanced initial capacity of 1166 mAh g-1 at C/20. After 50 cycles, the capacity gradually decreased to 710 mAh g-1 and was maintained stable after 220 cycles at C/10. A remarkable capacity of 889 mAh g-1 at C/2 was achieved. In comparison, the ASSLSBs using VGCF as carbon additive delivered a low rate capacity of 100 mAh g-1 at C/2.

Mechanistic Insight into Li–Host Interactions in Carbon Hosts for Reversible Li Metal Storage

In recent years, the industrial requirements for rechargeable batteries in terms of energy density have continuously increased owing to the widespread adoption of portable electronic devices and electric vehicles. Li metal has been identified as a promising anode material to meet the ever-increasing demand for rechargeable batteries with high energy densities because of its low redox potential (−3.04 V vs. standard hydrogen electrode)and high specific capacity (3860 mAh g−1) [1]. Despite these advantages, the commercial use of Li metal anodes has been hindered by unresolved critical issues, such as the uncontrollable growth of Li dendrites and the severe volume changes during cycling. In practice, the dendritic growth of Li deposits causes the formation of dead Li species and triggers internal short-circuiting of batteries during cycling, leading to a significant loss of reversibility and raising safety concerns. Moreover, large volume changes in the Li metal anode during Li plating–stripping, which originate from the “hostless” character of the Li metal, impose severe stresses on the solid–electrolyte interphase (SEI) layers, and thus reducing the mechanical stability of SEIs. Once the SEI layers are cracked or fractured, bare Li metal is exposed to the electrolyte, leading to the continuous formation of thick SEI layers on the anode surface. This is mainly responsible for the continuous, irreversible loss of active Li, i.e., low Coulombic efficiency and short cycle lifetimes.3D “host” architectures are beneficial for securing the dimensional stability of Li metal anodes by utilizing internal pores (i.e., free-spaces) as reservoirs for Li storage. Moreover, they provide large active surface areas and hence reduce the effective current densities, suppressing uneven Li plating (dendritic growth) during high-rate operations. Metal-organic framework (MOF)-derived carbon offers many advantages over conventional carbon materials in terms of specific surface area, pore volume, and structural tunability. Furthermore, the critical role of atomically dispersed heteroatoms has been verified in reducing the energy barriers for the nucleation and growth of Li [2].Herein, we report MOF-derived porous carbon hosts with strong Li–host interactions achieved by galvanically displaced lithiophilic seeds. Owing to the distinctive chemical and structural nature of zeolitic imidazolate frameworks (ZIF-8), atomically dispersed Zn can be spontaneously replaced by Ag with a strong lithiophilicity via a galvanic displacement (GD) reaction. Based on a comparative study of carbon hosts with different sizes, morphologies, and distributions of Ag, in particular, we assess the efficacy of lithiophilic Ag in promoting reversible Li storage inside porous carbon hosts. The strong Li–host interactions enabled by lithiophilic Ag effectively reduce the overpotentials for nucleation and growth of Li, and more importantly, the role of lithiophilic Ag in governing the reversibility of Li plating–stripping is discussed in terms of the spatial distribution characteristics of Ag. The atomically dispersed Ag triggers the outward growth of Li from the internal pores of the carbon host, showing a stable cycling performance (>745 cycles). Contrarily, the surface-anchored Ag nanoparticles induce uneven Li plating on the outer surface of the carbon host, resulting in a rapid performance drop (~305 cycles) during cycling. This work provides new insights into the development of advanced 3D host materials for reversible Li metal anodes by utilizing strong Li–host interactions.

Li Metal Storage in Porous Carbon Frameworks: Effect of Li–Substrate Interaction

Lithium-metal electrodes are of particular interest for next-generation rechargeable batteries because of their high specific capacity and low redox potential. Therefore, Li-metal-based batteries may afford higher energy densities than commercially available Li-ion batteries with graphite anodes. However, various bottlenecks have hampered the commercial development of these batteries, including uncontrolled Li dendrite formation and huge volume changes during cycling. Consequently, Li-metal batteries suffer from low Coulombic efficiency and poor cycling stability. In recent years, there has been extensive research on the design and construction of three-dimensional (3D) porous electrodes that can host metallic Li. However, the low pore utilization and uneven Li plating remain crucial issues. This can be understood in terms of electronic and ionic transport through the framework electrode. The carbon frameworks exhibit high electronic conductance; however, large resistance to Li+ migration in the electrolytes of internal and interparticle pores inhibits the penetration of Li+ deep into the electrode. In this work, we demonstrate that a strong interaction between Li and a lithiophilic nanolayer on a substrate plays a critical role in enhancing pore utilization in carbon framework electrodes. As a model architecture, we examine a Li storage process in a framework electrode consisting of porous carbon derived from metal-organic frameworks (MOFs) and a galvanically displaced Ag layer on a Cu substrate (Cu@Ag). The electrochemical experiments combined with operando XRD measurements and microstructural characterizations suggest that a lithiophilic Ag on the Cu substrate preferentially reacts with Li+ to form Li x Ag during the initial stage of Li plating. This Li x Ag phase acts as a seed that can regulate the subsequent Li plating, promoting confined Li storage in the carbon framework electrode while suppressing top plating. Because of these advantages, the MOF-C framework electrode on Cu@Ag exhibits better cycling stability (>250 cycles) than the MOF-C framework electrode on Cu (140cycles). However, when the thickness of the MOF-C framework is increased to 90 μm, the diffraction peak for Ag remains dominant throughout Li plating-stripping, and the formation of Li x Ag alloys is not clearly detectable in the diffraction patterns, suggesting that only a limited amount of Ag is involved in the alloying reaction with Li+. Based on the computational studies, the efficacy of lithiophilic layers toward improving pore utilization is discussed in terms of the kinetic competition between Li+ transport through porous channels and the interfacial reaction of Li+ with the substrate. This study conveys an important message that the Li-substrate interaction plays a vital role in promoting the confined Li storage; hence, it should be considered a key design factor for porous carbon frameworks with high capacity and long cycle lifetime.References Yun, H. R. Shin, E.-S. Won, H. C. Kang, J.-W. Lee, Confined Li metal storage in porous carbon frameworks promoted by strong Li-substrate interaction, Chem. Eng. J. 430 (2022) 132897.Jin, Y. Ye, Y. Niu, Y. Xu, H. Jin, J. Wang, Z. Sun, A. Cao, X. Wu, Y. Luo, H. Ji, L. J. Wan, Solid-solution-based metal alloy phase for highly reversible lithium metal anode, J. Am. Chem. Soc. 142 (2020) 8818–8826.Kim, J. Lee, J. Yun, S.H. Choi, S.A. Han, J. Moon, J.H. Kim, J.-W. Lee, M.-S. Park, Functionality of dual-phase lithium storage in a porous carbon host for lithium-metal anode, Adv. Funct. Mater. 30 (2020) 1910538.

Novel porous thermosensitive gel electrolytes for wearable thermo-electrochemical cells

Thermo-electrochemical cells (TECs) represent an efficient and low-cost heat-harvesting device that can directly convert human body heat energy into electricity. However, the flexible, solid-state gelled electrolytes used in wearable thermocell devices suffer from poor mass transport of electrolyte. Here, a novel porous gel is developed via sodium acetate (NaAc) templates and freeze-drying treatment that is applied in p-type gelled electrolyte: poly-acrylamide (PAM) - K3/4[Fe(CN)6] and integrated into platinum (Pt) electrodes for wearable devices. Moreover, the guanidinium ([Gdm]+) is initially introduced into gelled electrolytes, and the p-type cell effectively boosts the maximum power density from 4.01 to 7.68 mW m−2 at ΔT = 10 °C, and exhibits a quick thermosensitive response under a broad temperature range (15 – 55 °C), which is sufficient for working conditions of wearable devices. The optimised porous gel host was also utilized in series with an n-type: PAM-FeCl2/3-HCl gelled electrolyte. The multiple thermocells (12 pairs) were further fabricated into a device by alternating p- and n-type cells in series. This device was found to output nearly 0.23 V at ΔT = 10 °C, and was manufactured into a flexible wearable device that was demonstrated to successfully harvest human body heat by both charging a supercapacitor (100 mF), and illuminating an LED, demonstrating the potential of actual application of our n-p-type in series devices.

One-Dimensional Porous Li-Confinable Hosts for High-Rate and Stable Li-Metal Batteries.

Li-confinable core-shell hosts have been extensively studied because they mitigate Li dendrite growth and volume change by reducing the effective current density and storing Li inside the core space during consecutive cycling. However, despite these fascinating features, these hosts suffer from unwanted Li growth on their surface (i.e., top plating) due to the carbon shell hindering Li-ion movement especially at higher current densities and capacities, resulting in poor electrochemical performance. In this study, we propose a one-dimensional porous Li-confinable host with lithiophilic Au (Au@PHCF), which is synthesized by a scalable dual-nozzle electrospinning. Because of the well-interconnected conductive networks forming three-dimensional structure, porous shell design enabling facile Li-ion transport, and hollow core space with lithiophilic Au storing metallic Li, the Au@PHCF can suppress the Li top plating and improve the Li stripping/plating efficiency compared to their counterparts even at 5 mA cm-2, eventually achieving stable cycling performances of the LiFePO4 full cell and Au@PHCF-Li symmetric cell for over 1000 and 2000 cycles, respectively. Finite element analysis reveals that the structural merit and lithiophilicity of Au enable fast reversible Li operation at the designated core space of the Au@PHCF, implying that the structural design of the Li-confinable host is crucial for the stable operation of promising Li-metal batteries at a practical test level.

Classification-based motion analysis of single-molecule trajectories using DiffusionLab

Single-particle tracking is a powerful approach to study the motion of individual molecules and particles. It can uncover heterogeneities that are invisible to ensemble techniques, which places it uniquely among techniques to study mass transport. Analysis of the trajectories obtained with single-particle tracking in inorganic porous hosts is often challenging, because trajectories are short and/or motion is heterogeneous. We present the DiffusionLab software package for motion analysis of such challenging data sets. Trajectories are first classified into populations with similar characteristics to which the motion analysis is tailored in a second step. DiffusionLab provides tools to classify trajectories based on the motion type either with machine learning or manually. It also offers quantitative mean squared displacement analysis of the trajectories. The software can compute the diffusion constant for an individual trajectory if it is sufficiently long, or the average diffusion constant for multiple shorter trajectories. We demonstrate the DiffusionLab approach via the analysis of a simulated data set with motion types frequently observed in inorganic porous hosts, such as zeolites. The software package with graphical user interface and its documentation are freely available.

Salt in matrix for thermochemical energy storage - A review

Thermal energy storage (TES) method plays a vital role in storing and retrieving thermal energy from various sources (e.g. solar energy, industrial waste heat). Among all viable options for the TES, the reversible reaction pathway of thermochemical energy storage (TCES) has proved an experimentally much efficient form of energy storage over the latent and sensible energy storage. This review article focuses on a solid-gas system with water as sorbate for the TCES. At the material level, emphasis is put on comparing various pure thermochemical materials (TCMs) and salt in matrix (SIM), a thermochemical compound with porous material as a host. The basis of comparison among the compounds has been energy density and cyclic stability. It has been found that a pure TCM offers higher energy storage density compared to the SIM, while the latter exhibits better thermal cyclic stability. The porous host increases the surface area of the TCM leading to better mass and energy transfer and also prevents the deliquescence of the salt during the hydration process. This study also focuses on the synthesis of SIM, properties of host materials for SIM, and the use of various characterization methodologies for the analysis of SIM.[copyright information to be updated in production process]

Fabrication of LiOH-metal organic framework derived hierarchical porous host carbon matrix composites for seasonal thermochemical energy storage

Fabrication of LiOH-metal organic framework derived hierarchical porous host carbon matrix composites for seasonal thermochemical energy storage

In-situ growth of iron nanoparticles on porous carbon nanofibers for structural high-performance lithium metal anode

Lithium metal anodes have attracted increasing attention in recent years. However, there are still significant challenges in the electrochemical cycle of lithium metals, including the growth of lithium dendrites, the formation of "dead lithium" layers, and unrestricted volume expansion. To solve these problems, using inexpensive acetylacetonate salt, polyacrylonitrile, and polymethyl methacrylate as raw materials, a 3D porous carbon nanofiber scaffold decorated with iron nanoparticles is reasonably designed by novel and unique in-situ growth method, without hazardous atmosphere, expensive catalyst deposition, and additional carbon sources. Notably, the obtained iron-doped 3D porous fibers can be used as lithium metal anode framework with low lithium deposition overpotential and long cycling stability under various current densities. The porous host structure can adapt to the inherent volume expansion and the transmission of lithium ions in the process of lithium plating/stripping, thereby improving the cycling stability. Density functional theory calculations indicate that carbon nanofibers decorated with Fe nanoparticles are more likely to absorb lithium atoms, resulting in more uniform lithium deposition. The present work provides a low-cost and scalable strategy for constructing 3D structural high-efficiency lithium metal anode, and opens new horizons for the research of lithium metal batteries and even other metal batteries.

Porous Polymers as Universal Reversal Agents for Heparin Anticoagulants through an Inclusion-Sequestration Mechanism.

Heparins are widely used anticoagulants for surgical procedures and extracorporeal therapies. However, all of them have bleeding risks. Protamine sulfate, the only clinically approved antidote for unfractionated heparin (UFH), has adverse effects. Moreover, protamine can only partially neutralize low-molecular-weight heparins (LMWHs) and is not effective for fondaparinux. Here, an inclusion-sequestration strategy for efficient neutralization of heparin anticoagulants by cationic porous supramolecular organic frameworks (SOFs) and porous organic polymers (POPs) is reported. Isothermal titration calorimetric and fluorescence experiments show strong binding affinities of these porous polymers toward heparins, whereas dynamic light scattering and zeta potential analysis confirm that the heparin sequences are adsorbed into the interior of the porous hosts. Activated partial thromboplastin time, anti-FXa, and thromboelastography assays indicate that their neutralization efficacies are higher than or as high as that of protamine for UFH and generally superior to protamine for LMWHs and fondaparinux, which is further confirmed by tail-transection model in mice and ex vivo aPTT or anti-FXa analysis in rats. Acute toxicity evaluations reveal that one of the SOFs displays outstanding biocompatibility. This work suggests that porous polymers can supply safe and rapid reversal of clinically used heparins, as protamine surrogates, providing an improved approach for their neutralization.

Low temperature synthesis of hierarchically porous carbon host for durable lithium-sulfur batteries

Porous carbons with abundant pores and good conductivity are the dominant sulfur host in lithium sulfur batteries. Herein, a facile simultaneous activation/carbonization with inexpensive FeCl3 and ZnCl2 as activators is employed to prepare sucrose derived porous carbon at low temperature of 600 °C. The as-prepared carbon materials not only have partial graphitization due to the FeCl3 catalysis, but also show abundant hierarchical porous structure with high specific surface area of 2104 m2 g−1 and large pore volume of 1.29 cm3 g−1, whilst obtaining a high yield of about 30 wt%. When used to encapsulate sulfur, the abundant porous structure is conductive to immobilizing polysulfides and buffering volume effect during charge/discharge. Owing to these structure merits and good electrical conductivity, the corresponding porous carbon/sulfur cathode with a sulfur content of 53 wt% delivers high first discharge capacity of 811 mAh g−1 at 0.2C. Even with 75 wt% sulfur, the reversible capacity of 446 mAh g−1 are also obtained after 200 cycles at 0.2C. Especially, a durable long life of 1000 cycles with a low capacity decay of 0.035% per cycle can be achieved at 1C when the sulfur content is 45 wt%. This work provides a scientific foundation for preparing high-performance porous carbon applied in energy-related storage/conversion.

A novel design of 3D carbon host for stable lithium metal anode

AbstractRational design of porous conductive hosts with high electrical conductivity, large surface area, and adequate interior space is desirable to suppressing dendritic lithium growth and accommodating large volume change of lithium metal anode during the Li plating/stripping process. However, due to the conductive nature of the conductive hosts, Li is easily deposited directly on the top of the hosts, which hinders it from fully functioning. To circumvent the issue, in this study, we designed a novel porous carbon host with a gradient‐pore‐size structure based on one‐dimensional (1D) carbon with different diameters. With this kind of host, stable cycling with high and stable Coulombic efficiency of ~98% is achieved at 0.5 mA cm−2 with an areal capacity of 1 mAh cm−2 over 320 cycles. In contrast, the normal three‐dimensional (3D) carbon nanotube host presents a moss‐like Li morphology with wildly fluctuating Coulombic efficiency after 100 cycles. The results reveal that the unique gradient‐pore‐size structure of the 3D conductive host greatly improves the performance of lithium metal batteries.

Minimizing Carbon Content with Three‐in‐One Functionalized Nano Conductive Ceramics: Toward More Practical and Safer S Cathodes of Li‐S Cells

Using porous carbon hosts in cathodes of Li‐S cells can disperse S actives and offset their poor electrical conductivity. However, such reservoirs would in turn absorb excess electrolyte solvents to S‐unfilled regions, causing the electrolyte overconsumption, specific energy decline, and even safety hazards for battery devices. To build better cathodes, we propose to substitute carbons by In‐doped SnO2 (ITO) nano ceramics that own three‐in‐one functionalities: 1) using conductive ITO enables minimizing the total carbon content to an extremely low mass ratio (~3%) in cathodes, elevating the electrode tap density and averting the electrolyte overuse; 2) polar ITO nanoclusters can serve as robust anchors toward Li polysulfide (LiPS) by electrostatic adsorption or chemical bond interactions; 3) they offer catalysis centers for liquid–solid phase conversions of S‐based actives. Also, such ceramics are intrinsically nonflammable, preventing S cathodes away from thermal runaway or explosion. These merits entail our configured cathodes with high tap density (1.54 g cm−3), less electrolyte usage, good security for flame retardance, and decent Li‐storage behaviors. With lean and LiNO3‐free electrolyte, packed full cells exhibit excellent redox kinetics, suppressed LiPS shuttling, and excellent cyclability. This may trigger great research enthusiasm in rational design of low‐carbon and safer S cathodes.

Porous Liquids: Computational Design for Targeted Gas Adsorption.

In this Perspective, we present the unique gas adsorption capabilities of porous liquids (PLs) and the value of complex computational methods in the design of PL compositions. Traditionally, liquids only contain transient pore space between molecules that limit long-term gas capture. However, PLs are stable fluids that that contain permanent porosity due to the combination of a rigid porous host structure and a solvent. PLs exhibit remarkable adsorption and separation properties, including increased solubility and selectivity. The unique gas adsorption properties of PLs are based on their structure, which exhibits multiple gas binding sites in the pore and on the cage surface, varying binding mechanisms including hydrogen-bonding and π-π interactions, and selective diffusion in the solvent. Tunable PL compositions will require fundamental investigations of competitive gas binding mechanisms, thermal effects on binding site stability, and the role of nanoconfinement on gas and solvent diffusion that can be accelerated through molecular modeling. With these new insights PLs promise to be an exceptional material class with tunable properties for targeted gas adsorption.

Porous membrane host-derived in-situ polymer electrolytes with double-stabilized electrode interface enable long cycling lithium metal batteries

• DOL polymerized in-situ in the porous PVDF-HFP host to form the PVDF-HFP/ PDOL electrolytes. • Intimate contact in the double electrode interfaces have been created via the in-situ method. • The high lithium-ion transference number could be possibly attributed to the PVDF-HFP network. • Synergetic effect by SN and FEC improves the battery performance. • The Li/LiFePO 4 cell delivers capacity retention of 94.99% after 1000 cycles at room temperature. The application of solid polymer electrolytes (SPEs) has been impeded by the low ionic conductivity, narrow oxidation potential and poor mechanical strength. Herein, we designed a novel in-situ PVDF-HFP/Poly 1,3-dioxolane (PDOL) polymer electrolyte with dual-salts and functional plasticizers of succinonitrile (SN)/fluoroethylene carbonate (FEC). One of the dual-salts, Lithium difloro(oxalato)borate (LiDFOB), could initiate the polymerization of DOL in-situ in the porous PVDF-HFP host to improve the interfacial compatibility. SN is beneficial to the improvement of ionic conductivity and the stability of high voltage cathodes, while the FEC can generate the LiF-rich SEI on Li metal anode. The PVDF-HFP host can further restrict the motion of anion and increase the strength of the SPE. Therefore, the as-obtained SPE exhibits a thin thickness of ∼ 32 μm, high ionic conductivity of 1.06 × 10 −4 S cm −1 at room temperature, an enlarged electrochemical window of 5.86 V versus Li/Li + and high lithium-ion transference number t Li+ of 0.72. Benefited from the synergetic effect, the Li/LiFePO 4 cell delivers a high initial capacity of 141.7 mAh g −1 at 2C with a capacity retention of 94.99% after 1000 cycles. This three-dimensional porous film-derived in-situ polymer electrolytes provide a new sight and simple strategy for designing polymer electrolytes, exhibiting attractive potential in flexible and high-energy–density solid-state batteries.

A 3D Hierarchical Host with Enhanced Sodiophilicity Enabling Anode‐Free Sodium‐Metal Batteries (Adv. Mater. 14/2022)

Sodium-Metal Batteries In article number 2109767, Byung-Hyun Kim, Bumjoon J. Kim, Seung Woo Lee, and co-workers report anode-free sodium-metal batteries. The cover image depicts two batteries: the left shows typical sodium-metal batteries, where the continuous dendrite growth in the sodium-metal anodes causes a short-circuit, resulting in battery failure. Contrarily, the right shows highly reversible porous carbon hosts with carbon-shell-coated Fe nanoparticles for the sodium-metal anode, allowing superior cycling performance and improving the energy density of the batteries.

A MOF‐Derivative Decorated Hierarchical Porous Host Enabling Ultrahigh Rates and Superior Long‐Term Cycling of Dendrite‐Free Zn Metal Anodes (Adv. Mater. 14/2022)

Zinc-Metal Batteries In article number 2110047, Hongpeng Li, Lichao Tan, Zhongwei Chen and co-workers report a novel 3D host for Zn-metal anodes fabricated by assembling carbon nanotubes and graphene into a hierarchical porous structure, followed by decorating with Zn metal–organic framework (Zn-MOF) derivatives. The mechanically robust 3D host with high zincophilicity and conductivity could address the issues of dendrite growth, thereby enabling high-energy-density Zn-metal batteries.

Fundamental Study of the Optical and Vibrational Properties of Fx-AZB@MOF systems as Functions of Dye Substitution and the Loading Amount.

Controlling the switching efficiency of photoactive hybrid systems is an obligatory key prerequisite for systematically improving the design of functional materials. By modulating the degree of fluorination and the amount being embedded into porous hosts, the E/Z ratios of fluorinated azobenzenes were adjusted as both functions of substitution and the degree of loading. Octafluoroazobenzene (F8-AZB) and perfluoroazobenzene (F10-AZB) were inserted into porous DMOF-1. Especially for perfluoroazobenzene (F10-AZB), an immense stabilization of the E isomer was observed. In complementary molecular dynamics simulations performed at the DFTB (density functional tight binding) level, an in-depth characterization of the interactions of the different photoisomers and the host structure was carried out. On the basis of the resulting structural and energetic data, the experimentally observed increase in the amount of the Z conformer for F8-AZB can be explained, while the stabilization of E-F10-AZB can be directly related to a fundamentally different interaction motif compared to its tetra- and octafluorinated counterparts.

On the issue of textured crystallization of Ba(NO3)2 in mesoporous SiO2: Raman spectroscopy and lattice dynamics analysis

The lattice dynamics of preferentially aligned nanocrystals formed upon drying of aqueous Ba(NO3)2 solutions in a mesoporous silica glass traversed by tubular pores of approximately 12 nm are explored by Raman scattering. To interpret the experiments on the confined nanocrystals polarized Raman spectra of bulk single crystals and X-ray diffraction experiments are also performed. Since a cubic symmetry is inherent to Ba(NO3)2, a special Raman scattering geometry was utilized to separate the phonon modes of Ag and Eg species. Combining group-theory analysis and ab initio lattice dynamics calculations a full interpretation of all Raman lines of the bulk single crystal is achieved. Apart from a small confinement-induced line broadening, the peak positions and normalized peak intensities of the Raman spectra of the nanoconfined and macroscopic crystals are identical. Interestingly, the Raman scattering experiment indicates the existence of comparatively large,∼10–20 μm, single-crystalline regions of Ba(NO3)2 embedded in the porous host, near three orders of magnitude larger than the average size of single nanopores. This is contrast to the initial assumption of non-interconnected pores. It rather indicates an inter-pore propagation of the crystallization front, presumably via microporosity in the pore walls.

Covalent S and Cl grafted porous carbon host realized via the one-step pyrolysis method results in boosted Li–O2 battery performances

Li–O2 battery has attracted wide attention because it can satisfy the need for a new energy storage system with high energy density. However, poor oxygen reduction (ORR)/oxygen evolution (OER) kinetics involving Li2O2 formation/decomposition is a major obstacle to its development. By designing suitable cathode with desired structure and surface electronic states, the formation/morphology of Li2O2 and the reaction kinetics of charge process can be efficiently optimized simultaneously. In this work, a novel sulfur (S) and chlorine (Cl) co-doped porous carbon (CSC) were synthesized by one-step pyrolysis strategy, and the amount of heterogeneous atoms could be flexibly controlled by different calcination temperatures. Experimental combined with theoretical calculations show that the content of CCl bond plays an important role in the adsorption of intermediate LiO2, thus regulating the morphology of Li2O2 and ultimately affecting the release of battery energy. The CS bond mainly acts on the dynamics of the ORR and OER processes, which has an important influence on improving the round-trip efficiency of the battery. Benefiting from the synergistic effect of heteroatoms, the electrochemical performances of the Li–O2 battery, including round-trip efficiency, discharge capacity and cycling stability are greatly improved.