Shell Modulation of Hollow Metal Sulfide Nanocomposite for Stable Potassium Storage at Room and High Temperature.

The large size of K-ion makes the pursuit of stable high-capacity anodes for K-ion batteries (KIBs) a formidable challenge, particularly for high temperature KIBs as the electrode instability becomes more aggravated with temperature climbing. Herein, we demonstrate that a hollow ZnS@C nanocomposite (h-ZnS@C) with a precise shell modulation can resist electrode disintegration to enable stable high-capacity potassium storage at room and high temperature. Based on a model electrode, we identify an interesting structure-function correlation of the h-ZnS@C: with an increase in the shell thickness, the cyclability increases while the rate and capacity decreases, shedding light on the design of high-performance h-ZnS@C anodes via engineering the shell thickness. Typically, the h-ZnS@C anode with a shell thickness of 60 nm can deliver an impressive comprehensive performance at room temperature; the h-ZnS@C with shell thickness increasing to 75 nm can achieve an extraordinary stability (88.6% capacity retention over 450 cycles) with a high capacity (450 mAh g-1) and a superb rate even at an extreme temperature of 60 ℃, which is much superior than those reported anodes. This contribution envisions new perspectives on rational design of functional metal sulfides composite toward high-performance KIBs with insights into the significant structure-function correlation.

Conductive Metal-Organic Framework with Superior Redox Activity as a Stable High-Capacity Anode for High-Temperature K-Ion Batteries.

High-temperature rechargeable batteries are essential for energy storage in elevated-temperature situations. Due to the resource abundance of potassium, high-temperature K-ion batteries are drawing increasing research interest. However, raising the working temperature would aggravate the chemical and mechanical instability of the KIB anode, resulting in very fast capacity fading, especially when high capacity is pursued. Here, we demonstrated that a porous conductive metal-organic framework (MOF), which is constructed by N-rich aromatic molecules and CuO4 units via π-d conjugation, could provide multiple accessible redox-active sites and promised robust structure stability for efficient potassium storage at high temperatures. Even working at 60 °C, this MOF anode could deliver high initial capacity (455 mAh g-1), impressive rate, and extraordinary cyclability (96.7% capacity retention for 1600 cycles), which is much better than those of reported high-temperature KIB anodes. The mechanistic study revealed that C═N groups and CuO4 units contributed abundant redox-active sites; the synergistic effect of π-d conjugated character and reticular porous architecture facilitated the K+/e- transport and ensured an insoluble electrode with small volume deformation, thus achieving stable high-capacity potassium storage.

Facile Fabrication of Hollow Nanoporous Carbon Architectures by Controlling MOF Crystalline Inhomogeneity for Ultra-Stable Na-Ion Storage.

Hollow nanoporous carbon architectures (HNCs) present significant utilitarian value for a wide variety of applications. Facile and efficient preparation of HNCs has long been pursued but still remains challenging. Herein, we for the first time demonstrate that single-component metal-organic frameworks (MOFs) crystals, rather than the widely reported hybrid ones which necessitate tedious operations for preparation, could enable the facile and versatile syntheses of functional HNCs. By controlling the growth kinetics, the MOFs crystals (STU-1) are readily engineered into different shapes with designated styles of crystalline inhomogeneity. A subsequent one-step pyrolysis of these MOFs with intraparticle difference can induce a simultaneous self-hollowing and carbonization process, thereby producing various functional HNCs including yolk-shell polyhedrons, hollow microspheres, mesoporous architectures, and superstructures. Superior to the existing methods, this synthetic strategy relies only on the complex nature of single-component MOFs crystals without involving tedious operations like coating, etching, or ligand exchange, making it convenient, efficient, and easy to scale up. An ultra-stable Na-ion battery anode is demonstrated by the HNCs with extraordinary cyclability (93 % capacity retention over 8000 cycles), highlighting a high level of functionality of the HNCs.

Breaking Low-Strain and Deep-Potassiation Trade-Off in Alloy Anodes via Bonding Modulation for High-Performance K-Ion Batteries.

Alloy anode materials have garnered unprecedented attention for potassium storage due to their high theoretical capacity. However, the substantial structural strain associated with deep potassiation results in serious electrode fragmentation and inadequate K-alloying reactions. Effectively reconciling the trade-off between low-strain and deep-potassiation in alloy anodes poses a considerable challenge due to the larger size of K-ions compared to Li/Na-ions. In this study, we propose a chemical bonding modulation strategy through single-atom modification to address the volume expansion of alloy anodes during potassiation. Using black phosphorus (BP) as a representative and generalizing to other alloy anodes, we established a robust P-S covalent bonding network via sulfur doping. This network exhibits sustained stability across discharge-charge cycles, elevating the modulus of K-P compounds by 74%, effectively withstanding the high strain induced by the potassiation process. Additionally, the bonding modulation reduces the formation energies of potassium phosphides, facilitating a deeper potassiation of the BP anode. As a result, the modified BP anode exhibits a high reversible capacity and extended operational lifespan, coupled with a high areal capacity. This work introduces a new perspective on overcoming the trade-off between low-strain and deep-potassiation in alloy anodes for the development of high-energy and stable potassium-ion batteries.

Ultrafast Photocatalytic Detoxification of Mustard Gas Simulants by a Mesoporous Metal-Organic Framework with Dangling Porphyrin Molecules.

Developing effective catalysts to degrade chemical warfare agents is of great significance. Herein, a mesoporous MIL-101(Cr) composite material dangled with porphyrin molecules (denote as TCPP@MIL-101(Cr), TCPP = tetra(4-carboxyphenyl)porphyrin) is reported, which can be used as a heterogeneous photocatalyst for detoxification of mustard gas simulants 2-chloroethyl ethyl sulfide (CEES) to 2-chloroethyl ethyl sulfoxide (CEESO) with a half-life of 1 min. The catalytic performance of TCPP@MIL-101(Cr) is comparable to that of homogeneous molecular porphyrin. Mechanistic studies reveal that both 1 O2 and O2 •- are efficiently generated and play vital roles in the oxidation reaction. Gold nanoparticles (AuNPs) are attached to the TCPP@MIL-101(Cr) to further enhance the catalytic activity with a benchmark half-life of 45 s, which is the fastest record so far. A medical mask loaded TCPP@MIL-101(Cr) is fabricated for practical applications, which can selectively photoxidize CEES to CEESO under sunlight and air atmosphere, exhibiting the best degradation performance among the reported fabric-like composite materials.

Multiple Accessible Redox-Active Sites in a Robust Covalent Organic Framework for High-Performance Potassium Storage.

Covalent organic framework (COF) materials with porous character and robust structure have significant applied implications for K-ion battery (KIB) anodes, but they are limited by the low reversible capacity and inferior rate capability. Here, based on theoretical calculations, we identified that a porous bulk COF featuring numerous pyrazines and carbonyls in the π-conjugated periodic skeleton could provide multiple accessible redox-active sites for high-performance potassium storage. Its porous structure with a surface-dominated storage mechanism enabled the fast and stable storage of K-ions. Its insolubility in organic electrolytes and small volumetric change after potassiation ensured a robust electrode for stable cycling. As a KIB anode, this bulk COF demonstrated an unprecedentedly outstanding combination of reversible capacity (423 mAh g-1 at 0.1 C), rate capability (185 mAh g-1 at 10 C), and cyclability. The theoretical simulation and comprehensive characterizations confirmed the active sites are contributed by C═O, C═N, and the cation-π effect.

Engineering Microstructure of a Robust Polymer Anode by Moderate Pyrolysis for High-Performance Sodium Storage.

Polymer anodes have inspired considerable research interest for Na-ion batteries (NIBs) owing to their high structural flexibility and resource sustainability but are limited by the sluggish electrode kinetics, insufficient cyclability, and inferior electronic conductivity which usually made a large fraction (20-50 wt %) of conductive carbon additive necessitated. Herein, using a polymeric carbon nitride (PCN) anode as an example, we demonstrated that a moderate pyrolysis of the polymer anode could not only reduce its optical bandgap to enhance its electronic conductivity but also tune its microstructures to facilitate Na+ transfer/storage and sustain the repeated sodiation/desodiation. When used as NIBs anode with 10 wt % conductive carbon adding for preparing the electrode film, the moderate-pyrolysis PCN can promise high specific capacity (351 mAh g-1 at 0.1C), superb rate capability (151 and 95 mAh g-1 at 10C and 20C, respectively), and ultrastable cyclability (88.5% capacity retention after 6500 cycles at 2C). This comprehensive battery performance is much better than that of the previously reported organic counterparts. Our finding opened a new avenue in designing high-performance polymer anode for Na-ion batteries.

Immobilizing Redox-Active Tricycloquinazoline into a 2D Conductive Metal-Organic Framework for Lithium Storage.

Heteroaromatic-conjugated aromatic molecules have inspired numerous interests in rechargeable batteries like Li-ion batteries, but were limited by low conductivity and easy dissolution in electrolytes. Herein, we immobilize a nitrogen-rich aromatic molecule tricycloquinazoline (TQ) and CuO4 unit into a two-dimensional (2D) conductive metal-organic framework (MOF) to unlock their potential for Li+ storage. TQ was identified redox activity with Li+ for the first time. With a synergistic effect of TQ and CuO4 unit, the 2D conductive MOF, named Cu-HHTQ (HHTQ=2,3,7,8,12,13-hexahydroxytricycloquinazoline), can facilitate the Li+ /e- transport and ensure a resilient electrode, resulting in a high capacity of 657.6 mAh g-1 at 600 mA g-1 with extraordinary high-rate capability and impressive cyclability. Our findings highlight an efficient strategy of constructing electrode materials for energy storage with combining multiple redox-active moieties into conductive MOFs.

Manipulating Particle Chemistry for Hollow Carbon-based Nanospheres: Synthesis Strategies, Mechanistic Insights, and Electrochemical Applications.

Hollow carbon-based nanospheres (HCNs) have been demonstrated to show promising potential in a large variety of research fields, particularly electrochemical devices for energy conversion/storage. The current synthetic protocols for HCNs largely rely on template-based routes (TBRs), which are conceptually straightforward in creating hollow structures but challenged by the time-consuming operations with a low yield in product as well as serious environmental concerns caused by hazardous etching agents. Meanwhile, they showed inadequate ability to build complex carbon-related architectures. Innovative strategies for HCNs free from extra templates thus are highly desirable and are expected to not only ensure precise control of the key structural parameters of hollow architectures with designated functionalities, but also be environmentally benign and scalable approaches suited for their practical applications.In this Account, we outline our recent research progress on the development of template-free protocols for the creation of HCNs with a focus on the acquired mechanical insight into the hollowing mechanism when no extra templates were involved. We demonstrated that carbon-based particles themselves could act as versatile platforms to create hollow architectures through an effective modulation of their inner chemistry. By means of reaction control, the precursor particles were synthesized into solid ones with a well-designed inhomogeneity inside in the form of different chemical parameters such as molecular weight, crystallization degree, and chemical reactivity, by which we not only can create hollow structures inside particles but also have the ability to tune the key features including compositions, porosity, and dimensional architectures. Accordingly, the functionalities of the prepared HCNs could be systematically altered or optimized for their applications. Importantly, the discussed synthesis approaches are facile and environmentally benign processes with potential for scale-up production.The nanoengineering of HNCs is found to be of special importance for their application in a large variety of electrochemical energy storage and conversion systems where the charge transfer and structural stability become a serious concern. Particular attention in this Account is therefore directed to the potential of HCNs in battery systems such as sodium ion batteries (NIBs) and potassium ion batteries (KIBs), whose electrochemical performances are plagued by the destructive volumetric deformation and sluggish charge diffusion during the intercalation/deintercalation of large-size Na+ or K+. We demonstrated that precise control of the multidimensional factors of the HCNs is critical to offer an optimized design of sufficient reactive sites, excellent charge and mass transport kinetics, and resilient electrode structure and also provide a model system suitable for the study of complicated metal-ion storage mechanisms, such as Na+ storage in a hard carbon anode. We expect that this Account will spark new endeavors in the development of HCNs for various applications including energy conversion and storage, catalysis, biomedicine, and adsorption.

A Black Phosphorus-Graphite Composite Anode for Li-/Na-/K-Ion Batteries.

Black phosphorus (BP) is a desirable anode material for alkali metal ion storage owing to its high electronic/ionic conductivity and theoretical capacity. In-depth understanding of the redox reactions between BP and the alkali metal ions is key to reveal the potential and limitations of BP, and thus to guide the design of BP-based composites for high-performance alkali metal ion batteries. Comparative studies of the electrochemical reactions of Li+ , Na+ , and K+ with BP were performed. Ex situ X-ray absorption near-edge spectroscopy combined with theoretical calculation reveal the lowest utilization of BP for K+ storage than for Na+ and Li+ , which is ascribed to the highest formation energy and the lowest ion diffusion coefficient of the final potassiation product K3 P, compared with Li3 P and Na3 P. As a result, restricting the formation of K3 P by limiting the discharge voltage achieves a gravimetric capacity of 1300 mAh g-1 which retains at 600 mAh g-1 after 50 cycles at 0.25 A g-1 .

Phase Control on Surface for the Stabilization of High Energy Cathode Materials of Lithium Ion Batteries.

The development of high energy electrode materials for lithium ion batteries is challenged by their inherent instabilities, which become more aggravated as the energy densities continue to climb, accordingly causing increasing concerns on battery safety and reliability. Here, taking the high voltage cathode of LiNi0.5Mn1.5O4 as an example, we demonstrate a protocol to stabilize this cathode through a systematic phase modulating on its particle surface. We are able to transfer the spinel surface into a 30 nm shell composed of two functional phases including a rock-salt one and a layered one. The former is electrochemically inert for surface stabilization while the latter is designated to provide necessary electrochemical activity. The precise synthesis control enables us to tune the ratio of these two phases, and achieve an optimized balance between improved stability against structural degradation without sacrificing its capacity. This study highlights the critical importance of well-tailored surface phase property for the cathode stabilization of high energy lithium ion batteries.

A facile synthetic strategy for the creation of hollow noble metal/transition metal oxide nanocomposites.

We have reported an efficient synthetic protocol to build different hollow hybrid nanocomposites with tunable compositions, such as Au/TiO2, Pt/ZrO2, and Au/CexTi1-xO2. The noble metal nanoparticles were well encapsulated in a wall composed of the designated transition metal oxides, showing promising potential as stable catalysts as demonstrated by Pt/ZrO2 for methane combustion.

Controlling the Reaction of Nanoparticles for Hollow Metal Oxide Nanostructures.

Hollow nanostructures of metal oxides have found broad applications in different fields. Here, we reported a facile and versatile synthetic protocol to prepare hollow metal oxide nanospheres by modulating the chemical properties in solid nanoparticles. Our synthesis design starts with the precipitation of urea-containing metal oxalate, which is soluble in water but exists as solid nanospheres in ethanol. A controlled particle hydrolysis is achieved through the heating-induced urea decomposition, which transforms the particle composition in an outside-to-inside style: The reaction starts from the surface and then proceeds inward to gradually form a water-insoluble shell of basic metal oxalate. Such a reaction-induced solubility difference inside nanospheres becomes highly efficient to create a hollow structure through a simple water wash process. A following high temperature treatment forms hollow nanospheres of different metal oxides with structural features suited to their applications. For example, a high performance anode for Li-ion intercalation pseudocapacitor was demonstrated with the hollow and mesoporous Nb2O5 nanospheres.

Engineering Hollow Carbon Architecture for High-Performance K-Ion Battery Anode.

K-ion batteries (KIBs) are now drawing increasing research interest as an inexpensive alternative to Li-ion batteries (LIBs). However, due to the large size of K+, stable electrode materials capable of sustaining the repeated K+ intercalation/deintercalation cycles are extremely deficient especially if a satisfactory reversible capacity is expected. Herein, we demonstrated that the structural engineering of carbon into a hollow interconnected architecture, a shape similar to the neuron-cell network, promised high conceptual and technological potential for a high-performance KIB anode. Using melamine-formaldehyde resin as the starting material, we identify an interesting glass blowing effect of this polymeric precursor during its carbonization, which features a skeleton-softening process followed by its spontaneous hollowing. When used as a KIB anode, the carbon scaffold with interconnected hollow channels can ensure a resilient structure for a stable potassiation/depotassiation process and deliver an extraordinary capacity (340 mAh g-1 at 0.1 C) together with a superior cycling stability (no obvious fading over 150 cycles at 0.5 C).

Controlling the Compositional Chemistry in Single Nanoparticles for Functional Hollow Carbon Nanospheres.

Hollow carbon nanostructures have inspired numerous interests in areas such as energy conversion/storage, biomedicine, catalysis, and adsorption. Unfortunately, their synthesis mainly relies on template-based routes, which include tedious operating procedures and showed inadequate capability to build complex architectures. Here, by looking into the inner structure of single polymeric nanospheres, we identified the complicated compositional chemistry underneath their uniform shape, and confirmed that nanoparticles themselves stand for an effective and versatile synthetic platform for functional hollow carbon architectures. Using the formation of 3-aminophenol/formaldehyde resin as an example, we were able to tune its growth kinetics by controlling the molecular/environmental variables, forming resin nanospheres with designated styles of inner constitutional inhomogeneity. We confirmed that this intraparticle difference could be well exploited to create a large variety of hollow carbon architectures with desirable structural characters for their applications; for example, high-capacity anode for potassium-ion battery has been demonstrated with the multishelled hollow carbon nanospheres.

Microbial-Phosphorus-Enabled Synthesis of Phosphide Nanocomposites for Efficient Electrocatalysts.

Transition-metal phosphides have recently been identified as low-cost and efficient electrocatalysts that are highly active for the hydrogen evolution reaction. Unfortunately, to achieve a controlled phosphidation of nonprecious metals toward a desired nanostructure of metal phosphides, the synthetic processes usually turned complicated, high-cost, and even dangerous due to the reaction chemistry related to different phosphorus sources. It becomes even more challenging when considering the integration of those active metal phosphides with the structural engineering of their conductive matrix toward a favorable architecture for optimized catalytic performance. Herein, we identified that the biomass itself could act as an effective synthetic platform for the construction of supported metal phosphides by recovering its inner phosphorus upon reacting with transition-metals ions, forming well-dispersed, highly active nanoparticles of metal phosphides incorporated in the nanoporous carbon matrix, which promised high catalytic activity in the hydrogen evolution reaction. Our synthetic protocol not only provides a simple and effective strategy for the construction of a large variety of highly active nanoparticles of metal phosphides but also envisions new perspectives on an integrated utilization of the essential ingredients, particularly phosphorus, together with the innate architecture of the existing biomass for the creation of functional nanomaterials toward sustainable energy development.

Controlled formation of uniform nanoshells of manganese oxide and their potential in lithium ion batteries.

Uniform nanoshells of manganese oxides have been successfully prepared by controlling their growth kinetics in solution. The prepared manganese oxides show promising electrochemical performance when used as an anode material in lithium ion batteries.

Controlled Formation of Metal@Al2O3 Yolk-Shell Nanostructures with Improved Thermal Stability.

Yolk-shell structured nanomaterials have shown interesting potential in different areas due to their unique structural configurations. A successful construction of such a hybrid structure relies not only on the preparation of the core materials, but also on the capability to manipulate the outside wall. Typically, for Al2O3, it has been a tough issue in preparing it into a uniform nanoshell, making the use of Al2O3-based yolk-shell structures a challenging but long-awaited task. Here, in benefit of our success in the controlled formation of Al2O3 nanoshell, we demonstrated that yolk-shell structures with metal confined inside a hollow Al2O3 nanosphere could be successfully achieved. Different metals including Au, Pt, Pd have been demonstrated, forming a typical core@void@shell structure. We showed that the key parameters of the yolk-shell structure such as the shell thickness and the cavity size could be readily tuned. Due to the protection of a surrounding Al2O3 shell, the thermal stability of the interior metal nanoparticles could be substantially improved, resulting in promising performance for the catalytic CO oxidation as revealed by our preliminary test on Au@Al2O3.