Defect engineering of a TiO2 anatase/rutile homojunction accelerating sulfur redox kinetics for high-performance Na-S batteries.

Room-temperature sodium-sulfur (RT Na-S) batteries have the drawbacks of the poor shuttle effect of soluble sodium polysulfides (NaPSs) as well as slow sulfur redox kinetics, which result in poor cycling stability and low capacity, seriously affecting their extensive application. Herein, defect engineering is applied to construct rich oxygen vacancies at the interface of a TiO2 anatase/rutile homojunction (OV-TRA) to enhance sulfur affinity and redox reaction kinetics. Combining structural characterizations with electrochemical analysis reveals that OV-TRA well alleviates the shuttle effect of NaPSs and precipitates the deposition and diffusion kinetics of Na2S. Consequently, S/OV-TRA provides excellent electrochemical performance with a reversible capacity of 870 mA h g-1 at 0.1 C after 100 cycles and a long-term cycling capability of 759 mA h g-1 at 1 C after 1000 cycles. This work provides an effective interfacial defect engineering strategy to promote the application of metal oxides in RT Na-S batteries.

MOF-derived nitrogen-doped porous carbon nanofibers with interconnected channels for high-stability Li+/Na+ battery anodes.

Heteroatom-doped porous carbon materials have been widely used as anode materials for Li-ion and Na-ion batteries, however, improving the specific capacity and long-term cycling stability of ion batteries remains a major challenge. Here, we report a facile based metal-organic framework (MOFs) strategy to synthesize nitrogen-doped porous carbon nanofibers (NCNFs) with a large number of interconnected channels that can increase the contact area between the material and the electrolyte, shorten the diffusion distance between Li+/Na+ and the electrolyte, and relieve the volume expansion of the electrode material during cycling; the doping of nitrogen atoms can improve the conductivity and increase the active sites of the carbon material, can also affect the microstructure and electron distribution of the electrode material, thereby improving the electrochemical performance of the material. As expected, the obtained NCNFs-800 exhibited excellent electrochemical performance with high reversible capacity (for Li+ battery anodes: 1237 mA h g-1 at 100 mA g-1 after 200 cycles, for Na+ battery anodes: 323 mA h g-1 at 100 mA g-1 after 150 cycles) and long-term cycling stability (for Li+ battery anodes: 635 mA h g-1 at 2 A g-1 after 5000 cycles, for Na+ battery anodes: 194 mA h g-1 at 2 A g-1 after 5000 cycles).

Highly Flexible K-Intercalated MnO2 /Carbon Membrane for High-Performance Aqueous Zinc-Ion Battery Cathode.

The layered MnO2 is intensively investigated as one of the most promising cathode materials for aqueous zinc-ion batteries (AZIBs), but its commercialization is severely impeded by the challenging issues of the inferior intrinsic electronic conductivity and undesirable structural stability during the charge-discharge cycles. Herein, the lab-prepared flexible carbon membrane with highly electrical conductivity is first used as the matrix to generate ultrathin δ-MnO2 with an enlarged interlayer spacing induced by the K+ -intercalation to potentially alleviate the structural damage caused by H+ /Zn2+ co-intercalation, resulting in a high reversible capacity of 190 mAh g-1 at 3 A g-1 over 1000 cycles. The in situ/ex-situ characterizations and electrochemical analysis confirm that the enlarged interlayer spacing can provide free space for the reversible deintercalation/intercalation of H+ /Zn2+ in the structure of δ-MnO2 , and H+ /Zn2+ co-intercalation mechanism contributes to the enhanced charge storage in the layered K+ -intercalated δ-MnO2 . This work provides a plausible way to construct a flexible carbon membrane-based cathode for high-performance AZIBs.

Nonsteroidal anti-inflammatory drug monitoring in serum: a Tb-MOF-based luminescent mixed matrix membrane detector with high sensitivity and reliability.

The identification of drugs or biomolecules for public health monitoring requires facile analytical technologies with excellent sensitivity, portability and reliability. In the past decades, different sensing materials have inspired the development of various bioanalytical strategies. However, sensing platforms based on powder materials are not suitable for medical diagnosis, which limits further exploration and application of biosensors. Herein, a point-of-care testing (POCT) membrane was designed from an energy competition mechanism and achieved the detection of the nonsteroidal antiphlogistic diclofenac, and exhibited remarkable testing efficacy at the ppb level. The mixed matrix membrane (MMM) sensor consists of electrospun polyacrylonitrile nanofibers and luminescent Tb-MOFs and possess the advantages of high stability, outstanding anti-interference ability, efficient detection (LOD = 98.5 ppb) and easy visual recognition. Furthermore, this MMM sensor exhibits excellent recyclability in serum, which is beneficial for developing a portable and convenient device to distinguish diclofenac in practical sensing applications. Meanwhile, the feasibility and mechanism of this recyclable sensor were verified by theory and experiments, indicating that it is a promising device for diclofenac detection in biological environments to evaluate the toxic effect caused by the accumulation of nonsteroidal drugs.

Surface Reconstruction of Co4N Coupled with CeO2 toward Enhanced Alkaline Oxygen Evolution Reaction.

Constructing the active interface in a heterojunction electrocatalyst is critical for the electron transfer and intermediate adsorption (O*, OH*, and HOO*) in alkaline oxygen evolution reaction (OER) but still remains challenging. Herein, a CeO2/Co4N heterostructure is rationally synthesized through the direct calcination of Ce[Co(CN)6], followed by thermal nitridation. The in situ electrochemically generated CoOOH on the surface of Co4N serves as the active site for the OER, and the coupled CeO2 with oxygen vacancy can optimize the energy barrier of intermediate reactions of the OER, which simultaneously boosts the OER performance. Besides, electrochemical measurement results demonstrate that oxygen vacancies in CeO2 and optimized absorption free energy originating from the electron transfer between CeO2 and CoOOH contribute to enhanced OER kinetics. This work provides new insight into regulating the interface heterostructure to rationally design efficient OER electrocatalysts under alkaline conditions.

Optimizing the Interlayer Spacing of Heteroatom-Doped Carbon Nanofibers toward Ultrahigh Potassium-Storage Performances.

Precise control over the interlayer spacing for K+ intercalation is an effective approach to boost the potassium-storage performances in carbonaceous materials. Herein, we first found that the optimal interlayer spacing for K+ intercalation is around 0.38 nm for N, O codoped carbon nanofibers (NOCNs), displaying a reversible capacity of 627 mAh g-1 at 0.1 A g-1 after 200 cycles, excellent rate capability (123 mAh g-1 at 20 A g-1), and ultrastable cycling stability (262 mAh g-1 at 5 A g-1 after 10 000 cycles). Such good potassium-storage performances have never been reported in carbonaceous materials. The theoretical calculations and electrochemical studies reveal that the optimal interlayer spacing and N, O heteroatom-induced active sites work together to provide an intercalation-adsorption mechanism for storing K+ in carbonaceous materials. This work facilitates the understanding of the role of the critical interlayer spacing for K+ intercalation in carbonaceous materials.

Boosting the K+-adsorption capacity in edge-nitrogen doped hierarchically porous carbon spheres for ultrastable potassium ion battery anodes.

Although carbon materials have great potential for potassium ion battery (KIB) anodes due to their structural stability and abundant carbon-containing resources, the limited K+-intercalated capacity impedes their extensive applications in energy storage devices. Current research studies focus on improving the surface-induced capacitive behavior to boost the potassium storage capacity of carbon materials. Herein, we designed edge-nitrogen (pyridinic-N and pyrrolic-N) doped carbon spheres with a hierarchically porous structure to achieve high potassium storage properties. The electrochemical tests confirmed that the edge-nitrogen induced active sites were conducive for the adsorption of K+, and the hierarchical porous structure promoted the generation of stable solid electrolyte interphase (SEI) films, both of which endow the resulting materials with a high reversible capacity of 381.7 mA h g-1 at 0.1 A g-1 over 200 cycles and an excellent rate capability of 178.2 mA h g-1 at 5 A g-1. Even at 5 A g-1, the long-term cycling stability of 5000 cycles was achieved with a reversible capacity of 190.1 mA h g-1. This work contributes to deeply understand the role of the synergistic effect of edge-nitrogen induced active sites and the hierarchical porous structure in the potassium storage performances of carbon materials.

Constructing Graphitic-Nitrogen-Bonded Pentagons in Interlayer-Expanded Graphene Matrix toward Carbon-Based Electrocatalysts for Acidic Oxygen Reduction Reaction.

Metal-free carbon-based materials with high electrocatalytic activity are promising catalysts for the oxygen reduction reaction (ORR) in several renewable energy systems. However, the performance of carbon-based materials is far inferior to that of Pt-based catalysts in acid electrolytes. Here, a novel carbon-based electrocatalyst is reported toward ORR in 0.1 m HClO4 with half-wave potential of 0.81 V and better durability (100 h reaction time) than commercial 20 wt% Pt/C. It is achieved by constructing graphitic-nitrogen (GN)-bonded pentagons in graphitic carbon to improve the intrinsic activity of the carbon sites and increasing the amount of active sites via expanding the interlayer spacing. X-ray absorption spectroscopy and aberration-corrected electron microscopy characterizations confirm the formation of GN-bonded pentagons in this carbon material. Raman and X-ray photoelectron spectroscopy reveal that the activity is linearly associated with the amounts of both pentagons and adjacent GN atoms. Density function theory further demonstrates that adjacent GN atoms significantly increase the charge density at the carbon atom of a GN-bonded pentagon, which is the activity origin for the ORR.

A mild reduction of Co-doped MnO2 to create abundant oxygen vacancies and active sites for enhanced oxygen evolution reaction.

Efficient and non-precious-metal-based catalysts (e.g., manganese-based oxides) for the oxygen evolution reaction (OER) remain a substantial challenge. Creation of oxygen vacancies of manganese-based oxides with the aim to enhance their intrinsic activities is rarely reported, and there is a critical requirement for a mild and facile synthesis strategy to create abundant oxygen vacancies on manganese-based oxides. Herein, Co-doped MnO2 nanowires were reduced by NaBH4 solution at room temperature; then, MnCo2O4.5 nanosheets with abundant oxygen vacancies and active sites were formed on the surface of Co-doped MnO2 nanowires. Benefiting from the reduction strategy, the fabricated hierarchical Co-doped-MnO2@MnCo2O4.5 nanowire/nanosheet nanocomposites exhibit higher catalytic activity (an overpotential of 250 mV at a current density of 10 mA cm-2 in 1.0 M KOH solution) than pristine Co-doped MnO2 nanowires. The calculated TOF of Co-doped-MnO2@MnCo2O4.5 is 0.034 s-1 at the overpotential of 300 mV, which is 136-fold higher than that of Co-doped-MnO2. The excellent OER performance was attributed to the synergistic advantages of abundant oxygen vacancies and active sites over the hierarchical nanowire-nanosheet architectures.

Heteroatom-doped carbon materials with interconnected channels as ultrastable anodes for lithium/sodium ion batteries.

Carbon materials have been extensively investigated as promising negative electrode materials for lithium/sodium ion batteries. However, most common carbon materials always suffer from limitations in regards to high reversible capacity and long-term cycling stability because of their low theoretical specific capacities and sluggish kinetics. Herein, we report a facile MOF-derived strategy for the synthesis of nitrogen/oxygen co-doped porous carbon polyhedra (NOPCP) with abundant channel-connected cavities with their inner surface decorated with a large number of N and O atoms, which can provide a large number of active sites (defects and edge doping sites) for the sorption of Li+/Na+. These cavities can also be considered as "ponds" where the electrolyte is stored, which shortens the diffusion distance of ions during the discharge/charge process. When evaluated as an anode material for LIBs, NOPCP-600 delivers a high reversible capacity of 1663 mA h g-1 at 0.1 A g-1 after 120 cycles and superior cycling stability with a capacity of 667 mA h g-1 after 1000 cycles at 2 A g-1. For SIBs, NOPCP-600 delivers a high reversible capacity of 313 mA h g-1 at 0.1 A g-1 after 100 cycles and an excellent long-term cycling stability of 228 mA h g-1 at 1 A g-1 after 2000 cycles.

Synergistic Tuning of the Electronic Structure of Mo2C by P and Ni Codoping for Optimizing Electrocatalytic Hydrogen Evolution.

Developing earth-abundant and highly efficient nonprecious metal catalysts for hydrogen evolution reaction (HER) is critical for the storage and conversion of renewable energy sources. Molybdenum carbide (Mo2C) has been extensively investigated as one of the most promising nonprecious electrocatalysts for boosting HER because of its low cost, high electrical conductivity, good chemical structure, and similar electronic structure to that of Pt. However, Mo2C always exhibits the negative hydrogen-binding energy, which can largely prevent adsorbed H desorption during the HER process. Herein, we report P- and Ni-dual-doped Mo2C in porous nitrogen-doped carbon (P/Ni-Mo2C) as an electrocatalyst for the HER, exhibiting excellent activity and durability with a low overpotential of 165 mV at 10 mA cm-2 in alkaline electrolyte. Density functional theory (DFT) calculations proved that P and Ni acted as the anion and cation, respectively, to synergistically tune the electronic properties of Mo2C to decrease the negative hydrogen-binding energy, endowing the catalyst with excellent catalytic performance for the HER.

NiRu nanoparticles encapsulated in a nitrogen-doped carbon matrix as a highly efficient electrocatalyst for the hydrogen evolution reaction.

The design and fabrication of low-cost, efficient, and robust electrocatalysts for the hydrogen evolution reaction (HER) is of great importance in accelerating the development of water electrolysis technology. Herein, NiRu alloy nanostructures embedded in a nitrogen-doped carbon matrix (NiRu@NC) have been fabricated through a facile metal-organic framework-derived (MOF-derived) strategy. Benefiting from their advantages in the unique structures and components, the resulting NiRu@NC possesses excellent activity and durability towards the HER, which exhibits low overpotentials of 85 and 53 mV at a current density of 10 mA cm-2 in acidic and alkaline electrolytes, respectively. Furthermore, NiRu2@NC-600 also exhibits excellent hydrogen oxidation reaction (HOR) activity in an alkaline electrolyte. Therefore, this work provides a facile MOF-derived strategy for the design and synthesis of low-cost and efficient electrocatalysts for the HER.

Porous CuO@C composite as high-performance anode materials for lithium-ion batteries.

Though carbon matrices could effectively improve the electrical conductivity and accommodate the volume expansion of CuO-based anode materials for lithium ion batteries (LIBs), achieving an optimized utilization ratio of the active CuO component remains a big challenge. In this work, we developed a metal-organic framework (MOF)-derived strategy to synthesize ultrafine CuO nanoparticles embedded in a porous carbon matrix (CuO@C). Benefiting from its unique structure, the resulting CuO@C exhibits a high reversible capacity of 1024 mA h g-1 at 100 mA g-1 after 100 cycles and a long-term cycling stability with a reversible capacity of 613 mA h g-1 at 500 mA g-1 over 700 cycles. The outstanding Li-storage performances can be attributed to its porous carbon matrix and ultrafine CuO nanoparticles with more exposed active sites for electrochemical reactions.

MOF-derived hollow NiCo2O4 nanowires as stable Li-ion battery anodes.

Although binary metal oxides with high theoretical specific capacities and power densities are widely investigated as promising anode materials for lithium-ion batteries (LIBs), their poor cycling stability and huge volume expansion largely limit their extensive application in practical electrode materials. Herein, we report a facile strategy to synthesize hollow NiCo2O4 nanowires through direct calcination of binary metal-organic frameworks (MOFs) in air. When evaluated as an anode material for LIBs, NiCo2O4 nanowires deliver a reversible capacity of 1310 mA h g-1 at a current density of 100 mA g-1 after 100 cycles. Even at a high current density of 1 A g-1, NiCo2O4 nanowires exhibit long-term cycling stability with a capacity of 720 mA h g-1 after 1000 cycles. The outstanding lithium-storage performance can be attributed to the unique structures with 1D porous channels, which are beneficial for the fast transfer of Li+ ions and electrolyte and alleviate the strain caused by the volume expansion during cycling processes.

A novel self-assembled-derived 1D MnO2@Co3O4 composite as a high-performance Li-ion storage anode material.

Manganese dioxide (MnO2) is a high-performance anodic material and applied widely in lithium-ion batteries (LIBs). However, some intrinsic limitations originate from the low ionic conductivity, high polarization, and severe volume expansion of this type of material. In this work, we generated a one-dimensional porous MnO2@Co3O4 composite from a MnOOH@ZIF-67 precursor, which is synthesized via a self-assembly strategy. The one-dimensional porous structure provided more active sites and shorter-ion/electron-diffusion distance, thereby enabling higher Li+ storage capacity and better rate capability than a transition metal oxide alone. The Co3O4 coating buffered the volume change during Li+ insertion/extraction, leading to increased cycling stability of the electrode. When evaluated as the anode of LIBs, MnO2@Co3O4 exhibited a reversible capacity of 647 mA h g-1 at 2000 mA g-1 after 400 cycles. This excellent performance indicated that the MnO2@Co3O4 material could be an attractive potential candidate for Li+ storage.

The Effect of Constituent Ratios and Varisized Ammonium Salts on the Performance of Two-Dimensional Perovskite Materials.

Two-dimensional perovskite solar cells (PSCs) with high moisture resistance are a key topic in the photovoltaic field. However, their lower power conversion efficiencies (PCEs) in comparison to 3 D PSCs is still an urgent problem to be solved. It is vital to understand the impact of constituent ratios and ammonium salt sizes on the photovoltaic performance and humidity stability. Based on the formula of (RNH3 )2 (MA)n-1 Pbn I3n+1 (n=1, 3, 5, 7, 9, and 11), a series of 2 D perovskites is prepared by introducing varisized ammonium salts of ethylammonium iodide (EAI), propylammonium iodide (PAI), and butylammonium iodide (BAI). The effects of the constituent ratios and varisized ammonium salts on the properties of the 2 D perovskites were studied. 2 D perovskite devices based on larger n and smaller ammonium salt size are found to exhibit better performances. However, the moisture resistance of the 2 D perovskite devices is higher when n is smaller and the ammonium salt size is larger. Therefore, the EA2 MA10 Pb11 I34 (n=11) 2 D perovskite device displays the best photovoltaic performance, with the highest PCE of 16.93 %, whereas BA2 MA2 Pb3 I10 (n=3) 2 D perovskite, with the largest contact angle of 79.8°, can retain over 85 % of the initial PCE after 1440 h aging at 50 % relative humidity. This work indicates the PCE and stability of 2 D perovskites can be conveniently and effectively adjusted by controlling the 2 D constituent ratios and ammonium salt sizes, so as to obtain efficient 2 D PSCs with high stability.

MOF-derived self-assembled ZnO/Co3O4 nanocomposite clusters as high-performance anodes for lithium-ion batteries.

Although different kinds of metal oxide nanoparticles are extensively investigated as anode materials for lithium-ion batteries (LIBs), their cycle life and energy/power density are still not suitable for commercial applications. Metal oxides have a large storage capacity, but they suffer from low electrical conductivity and severe volume change during the charge/discharge process. Herein, we present a facile route to prepare self-assembled ZnO/Co3O4 nanocomposite clusters through calcination of preformed Prussian Blue Analogue (PBA) Zn3[Co(CN)6]2 nanospheres. These self-assembled ZnO/Co3O4 nanocomposite clusters exhibit superior lithium storage capabilities with good cycling properties. A reversible capacity of 957 mA h g(-1) was retained at a current density of 100 mA g(-1) up to 100 cycles. The enhanced electrochemical performance of the ZnO/Co3O4 nanocomposite anode can be ascribed to the rational design of the self-assembled cluster structures and the synergetic effect of two-component functional nanoparticle systems.

MOF-derived ultrafine MnO nanocrystals embedded in a porous carbon matrix as high-performance anodes for lithium-ion batteries.

Although MnO has been demonstrated to be a promising anode material for lithium-ion batteries (LIBs) in terms of its high theoretical capacity (755 mA h g(-1)), comparatively low voltage hysteresis (<0.8 V), low cost, and environmental benignity, the application of MnO as a practical electrode material is still hindered by many obstacles, including poor cycling stability and huge volume expansion during the charge/discharge process. Herein, we report a facile and scalable metal-organic framework-derived route for the in situ fabrication of ultrafine MnO nanocrystals encapsulated in a porous carbon matrix, where nanopores increase active sites to store redox ions and enhance ionic diffusivity to encapsulated MnO nanocrystals. As an anode material for lithium-ion batteries (LIBs), these MnO@C composites exhibited a high reversible specific capacity of 1221 mA h g(-1) after 100 cycles at a current density of 100 mA g(-1). The excellent electrochemical performance can be attributed to their unique structure with MnO nanocrystals dispersed uniformly inside a porous carbon matrix, which can largely enhance the electrical conductivity and effectively avoid the aggregation of MnO nanocrystals, and relieve the strain caused by the volumetric change during the charge/discharge process. This facile and economical strategy will extend the scope of metal-organic framework-derived synthesis for other materials in energy storage applications.

Nano electrochemical reactors of Fe2O3 nanoparticles embedded in shells of nitrogen-doped hollow carbon spheres as high-performance anodes for lithium-ion batteries.

Iron oxides are extensively investigated as anode materials for lithium-ion batteries (LIBs) because of their large specific capacities. However, they undergo huge volume changes during cycling that result in anode pulverization and loss of electrical connectivity. As a result, the capacity retention of the iron oxide anodes is poor and should be improved for commercial applications. Herein, we report the preparation of ultrasmall Fe2O3 nanoparticles embedded in nitrogen-doped hollow carbon sphere shells (Fe2O3@N-C) by the direct pyrolysis of Fe-based zeolitic imidazolate frameworks (Fe-ZIF) at 620 °C in air. As an anode material for LIBs, the capacity retained was 1573 mA h g(-1) after 50 cycles at a current density of 0.1 C (1 C = 1000 mA g(-1)). Even undergoing the high-rate capability test twice, it can still deliver a remarkably reversible and stable capacity of 1142 mA h g(-1) after 100 cycles at a current density of 1 C. The excellent electrochemical performance is attributed to the unique structure of ultrasmall Fe2O3 nanoparticles uniformly distributed in the shell of nitrogen-doped carbon spheres, which simultaneously solve the major problems of pulverization, facilitate rapid electrochemical kinetics, and effectively avoid the aggregation of Fe2O3 nanoparticles during de/lithiation. The novel method developed in this work for the synthesis of functional hybrid materials can be extended to the preparation of various MOFs-derived functional nanocomposites owing to the versatility of links and metal centers in MOFs.

Fe3O4@carbon@zeolitic imidazolate framework-8 nanoparticles as multifunctional pH-responsive drug delivery vehicles for tumor therapy in vivo.

Controlled drug release is a promising approach for cancer therapy due to its merits of reduced systemic toxicity and enhanced antitumor efficacy. Here, multifunctional Fe3O4@carbon@zeolitic imidazolate framework-8 (FCZ) hybrid nanoparticles (NPs) were successfully constructed. Owing to the porosity and acid-sensitivity of zeolitic imidazolate framework-8 (ZIF-8), FCZ NPs not only displayed an improved drug loading capacity compared to most of the polymeric nanocarriers, but also exhibited excellent pH-triggered release of doxorubicin (DOX) in vitro. Moreover, carbon dots (CDs) embedded in the porous carbon shell and superparamagnetic iron oxide nanocrystals could simultaneously function as intracellular fluorescence imaging and T2*-weighted magnetic resonance imaging (MRI) contrast agents, respectively. The results obtained from the MTT assay demonstrated good biocompatibility of FCZ NPs. DOX release experiments showed pH regulation-dominated drug release kinetics: a weak acidic pH in tumor areas could trigger sustained drug release, suggesting that FCZ NPs are ideal drug delivery systems. Moreover, the remarkable inhibition of tumor growth without side effects was confirmed in vivo. These results provide convincing evidence establishing the multifunctional FCZ NPs as promising candidates for tumor therapy.