Lithium–sulfur batteries are among the most promising electrochemical energy storage devices of the near future. Especially the low price and abundant availability of sulfur as the cathode material ...and the high theoretical capacity in comparison to state‐of‐the art lithium‐ion technologies are attractive features. Despite significant research achievements that have been made over the last years, fundamental (electro‐) chemical questions still remain unanswered. This review addresses ten crucial questions associated with lithium–sulfur batteries and critically evaluates current research with respect to them. The sulfur–carbon composite cathode is a particular focus, but its complex interplay with other hardware components in the cell, such as the electrolyte and the anode, necessitates a critical discussion of other cell components. Modern in situ characterisation methods are ideally suited to illuminate the role of each component. This article does not pretend to summarise all recently published data, but instead is a critical overview over lithium–sulfur batteries based on recent research findings.
Promising storage: This review addresses ten crucial questions associated with lithium–sulfur batteries and critically evaluates current research with respect to them. The sulfur–carbon composite cathode is in the particular focus, but its complex interplay with other hardware components, such as the electrolyte and the anode, necessitates a critical discussion as well.
Dynamic metal–organic frameworks (MOFs) represent a subgroup of frameworks featuring unique performance, as they are capable of adapting their pore size and/or the orientation of framework ...constituents in response to specific guest molecules such as gases or solutes and often outperform their rigid analogus in gas storage, sensing, or separation. In this review, the authors focus on recent methodical developments of advanced in situ diffraction and spectroscopic techniques for comprehensive characterization of porous frameworks. Examples for advanced instrumentation are highlighted for in situ nuclear magnetic resonance, electron paramagnetic resonance, and optical spectroscopies as well as X‐ray and neutron diffraction. Several examples of high‐resolution transmission electron microscopy (HRTEM) on MOFs are shown because HRTEM is an emerging technique for the characterization of time‐resolved structural dynamics in MOFs. These methods shed light on structural features and phase transitions of the host, its spin state, electronic structure, specific host–guest and guest–guest interactions, preferable adsorption sites, and bonding situation in the framework, focusing on the most prominent recent case studies. The synergistic development of novel in situ characterization methods and exploration of well‐defined model framework systems are crucial to advance the understanding of dynamic processes in porous materials in future.
Structural switchability, accompanied by a large breathing amplitude of the unit cell, is a unique phenomenon in flexible metal–organic frameworks (MOFs). Recent advances in the development of in situ spectroscopic (optical, nuclear magnetic and electron paramagnetic resonance) and diffraction (X‐ray, neutron and electron) techniques for monitoring the dynamic behavior of switchable MOFs upon applying external stimuli are reviewed.
Rattle‐type Fe3O4@SiO2 hollow mesoporous spheres with different particle sizes, different mesoporous shell thicknesses, and different levels of Fe3O4 content are prepared by using carbon spheres as ...templates. The effects of particle size and concentration of Fe3O4@SiO2 hollow mesoporous spheres on cell uptake and their in vitro cytotoxicity to HeLa cells are evaluated. The spheres exhibit relatively fast cell uptake. Concentrations of up to 150 µg mL−1 show no cytotoxicity, whereas a concentration of 200 µg mL−1 shows a small amount of cytotoxicity after 48 h of incubation. Doxorubicin hydrochloride (DOX), an anticancer drug, is loaded into the Fe3O4@SiO2 hollow mesoporous spheres, and the DOX‐loaded spheres exhibit a somewhat higher cytotoxicity than free DOX. These results indicate the potential of Fe3O4@SiO2 hollow mesoporous spheres for drug loading and delivery into cancer cells to induce cell death.
Hollow mesoporous spheres of Fe3O4@SiO2 exhibit relatively fast cell uptake and no cytotoxicity up to a concentration of 150 µg mL−1 after 48 h of incubation. Doxorubicin hydrochloride (DOX)‐loaded spheres exhibit a somewhat higher cytotoxicity than free DOX (see picture). The Fe3O4SiO2 spheres have potential for drug loading and delivery into cancer cells to induce cell death.
Abstract
Direct electrochemical reduction of CO
2
to fuels and chemicals using renewable electricity has attracted significant attention partly due to the fundamental challenges related to reactivity ...and selectivity, and partly due to its importance for industrial CO
2
-consuming gas diffusion cathodes. Here, we present advances in the understanding of trends in the CO
2
to CO electrocatalysis of metal- and nitrogen-doped porous carbons containing catalytically active M–N
x
moieties (M = Mn, Fe, Co, Ni, Cu). We investigate their intrinsic catalytic reactivity, CO turnover frequencies, CO faradaic efficiencies and demonstrate that Fe–N–C and especially Ni–N–C catalysts rival Au- and Ag-based catalysts. We model the catalytically active M–N
x
moieties using density functional theory and correlate the theoretical binding energies with the experiments to give reactivity-selectivity descriptors. This gives an atomic-scale mechanistic understanding of potential-dependent CO and hydrocarbon selectivity from the M–N
x
moieties and it provides predictive guidelines for the rational design of selective carbon-based CO
2
reduction catalysts.
A set of porous carbons has been prepared by chemical activation of various fungi-based chars with KOH. The resulting carbon materials have high surface areas (1600–2500m2/g) and pore volumes ...(0.80–1.56cm3/g), regardless of the char precursors. The porosities mainly derived from micropores in activated carbons strongly depend on the activation parameters (temperature and KOH amount). All activated carbons have uniform micropores with pore size of 0.8–0.9nm, but some have a second set of micropores (1.3–1.4nm pore size), further broadened to 1.9–2.1nm as a result of increasing either the activation temperature to 750°C or KOH/char mass ratio to 5/1. These fungi-based porous carbons achieve an excellent H2 uptake of up to 2.4wt% at 1bar and −196°C, being in agreement with results from other porous carbonaceous adsorbents reported in the literature. At high pressure (ca. 35bar), the saturated H2 uptake reaches 4.2–4.7wt% at −196°C for these fungi-based porous carbons. The results imply a great potential of these fungi-based porous carbons as H2 on-board storage media.
Enhancing ionic conductivity of quasi‐solid‐state electrolytes (QSSEs) is one of the top priorities, while conventional metal–organic frameworks (MOFs) severely impede ion migration due to their ...abundant grain boundaries. Herein, ZIF‐4 glass, a subset of MOFs, is reported as QSSEs (LGZ) for lithium‐metal batteries. With lean Li content (0.12 wt%) and solvent amount (19.4 wt%), LGZ can achieve a remarkable ion conductivity of 1.61 × 10−4 S cm−1 at 30 °C, higher than those of crystalline ZIF‐4‐based QSSEs (LCZ, 8.21 × 10−5 S cm−1) and the reported QSSEs containing high Li contents (0.32–5.4 wt%) and huge plasticizer (30–70 wt%). Even at −56.6 °C, LGZ can still deliver a conductivity of 5.96 × 10−6 S cm−1 (vs 4.51 × 10−7 S cm−1 for LCZ). Owing to the grain boundary‐free and isotropic properties of glassy ZIF‐4, the facilitated ion conduction enables a homogeneous ion flux, suppressing Li dendrites. When paired with LiFePO4 cathode, LGZ cell demonstrates a prominent cycling capacity of 101 mAh g−1 for 500 cycles at 1 C with the near‐utility retention, outperforming LCZ (30.7 mAh g−1) and the explored MOF‐/covalent–organic frameworks (COF)‐based QSSEs. Hence, MOF glasses will be a potential platform for practical quasi‐solid‐state batteries in the future.
Glassy metal–organic frameworks with lean Li content (0.12 wt%) and solvent amount (19.4 wt%) show a high ion conductivity, prominent dendritic suppression, and remarkable electrochemical performance when paired with a LiFePO4 cathode, probably due to their isotropic nature and reduced grain boundaries.
A new mesoporous metal–organic framework (MOF; DUT‐60) was conceptually designed in silico using Zn4O6+ nodes, ditopic and tritopic linkers to explore the stability limits of framework architectures ...with ultrahigh porosity. The robust ith‐d topology of DUT‐60 provides an average bulk and shear modulus (4.97 GPa and 0.50 GPa, respectively) for this ultra‐porous framework, a key prerequisite to suppress pore collapse during desolvation. Subsequently, a cluster precursor approach, resulting in minimal side product formation in the solvothermal synthesis, was used to produce DUT‐60, a new crystalline framework with the highest recorded accessible pore volume (5.02 cm3 g−1) surpassing all known crystalline framework materials.
Pores for thought: Computational prediction suggests DUT‐60 as a new framework with sufficient mechanical stability to enable exceptional gas accessible porosity. With an experimentally validated specific surface area of 7839 m2 g−1 and a specific pore volume of 5.02 cm3 g−1 DUT‐60 has the highest ever achieved porosity among all crystalline porous frameworks.
Recognising timescale as an adjustable dimension in porous solids provides a new perspective to develop novel four-dimensional framework materials. The deliberate design of three-dimensional porous ...framework architectures is a developed field; however, the understanding of dynamics in open frameworks leaves a number of key questions unanswered: What factors determine the spatiotemporal evolution of deformable networks? Can we deliberately engineer the response of dynamic materials along a time-axis? How can we engineer energy barriers for the selective recognition of molecules? Answering these questions will require significant methodological development to understand structural dynamics across a range of time and length scales.
Layered two‐dimensional (2D) conjugated metal–organic frameworks (MOFs) represent a family of rising electrocatalysts for the oxygen reduction reaction (ORR), due to the controllable architectures, ...excellent electrical conductivity, and highly exposed well‐defined molecular active sites. Herein, we report a copper phthalocyanine based 2D conjugated MOF with square‐planar cobalt bis(dihydroxy) complexes (Co‐O4) as linkages (PcCu‐O8‐Co) and layer‐stacked structures prepared via solvothermal synthesis. PcCu‐O8‐Co 2D MOF mixed with carbon nanotubes exhibits excellent electrocatalytic ORR activity (E1/2=0.83 V vs. RHE, n=3.93, and jL=5.3 mA cm−2) in alkaline media, which is the record value among the reported intrinsic MOF electrocatalysts. Supported by in situ Raman spectro‐electrochemistry and theoretical modeling as well as contrast catalytic tests, we identified the cobalt nodes as ORR active sites. Furthermore, when employed as a cathode electrocatalyst for zinc–air batteries, PcCu‐O8‐Co delivers a maximum power density of 94 mW cm−2, outperforming the state‐of‐the‐art Pt/C electrocatalysts (78.3 mW cm−2).
Thanks to the links: A copper phthalocyanine‐based 2D conjugated MOF with square‐planar cobalt bis(dihydroxy) units (Co‐O4) as linkages serves as an electrocatalyst for the oxygen reduction reaction with high catalytic activity (E1/2=0.83 V vs. RHE). The linking Co centers with optimized electronic structure (eg=1) are identified as the active sites.
Potassium‐ion batteries (PIBs) have emerged as a compelling complement to existing lithium‐ion batteries for large‐scale energy storage applications, due to the resource‐abundance of potassium, the ...low standard redox potential and high conductivity of K+‐based electrolytes. Rapid progress has been made in identifying suitable carbon anode materials to address the sluggish kinetics and huge volume variation problems caused by large‐size K+. However, most research into carbon materials has focused on structural design and performance optimization of one or several parameters, rather than considering the holistic performance especially for realistic applications. This perspective examines recent efforts to enhance the carbon anode performance in terms of initial Coulombic efficiency, capacity, rate capability, and cycle life. The balancing of the intercalation and surface‐driven capacitive mechanisms while designing carbon structures is emphasized, after which the compatibility with electrolyte and the cell assembly technologies should be considered under practical conditions. It is anticipated that this work will engender further intensive research that can be better aligned toward practical implementation of carbon materials for K+ storage.
For developing advanced carbon anode materials in potassium‐ion batteries, it is vital to well balance the diffusion‐controlled intercalation and surface‐driven capacitive mechanisms. Consequently, comprehensive optimization of initial Coulombic efficiency, capacity, rate capability, cycle life, and low‐potential plateau discharge/charge curves could be realized to be better aligned toward practical implementation of carbon materials for K+ storage.
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