ZIF-67-Derived CoSe/NC Composites as Anode Materials for Lithium-Ion Batteries

Activation of peroxymonosulfate with ZIF-67-derived Co/N-doped porous carbon nanocubes for the degradation of Congo red dye

In this study, porous carbon nanocubes encapsulated magnetic metallic Co nanoparticles (denoted as Co@N-PCNC) was prepared via pyrolyzing ZIF-67 nanocubes precursor at 600 °C and characterized by various technologies. It was used to activate peroxymonosulfate (PMS) to degrade Congo red (CR) dye efficiently. Over 98.45% of 50 mg L-1 CR was degraded using 0.033 mM PMS activated by 75 mg L-1 Co@N-PCNC within 12 min. The free radical quenching experiments were performed to reveal the nature of the reactive oxygen species radicals generated throughout the catalytic oxidation of CR. The effects of common inorganic anions and the water matrix on CR removal were studied. Moreover, the results of the kinetic study revealed the suitability of the pseudo-first-order and Langmuir-Hinshelwood kinetic models for illustrating CR degradation using the Co@N-PCNC/PMS system. Ultimately, the Co@N-PCNC displayed good operational stability, and after five cycles, the CR removal rate can still maintain over 90% after 12 min.

ZIF-67 MOF-Derived Mn3O4 @ N-Doped C as a Supercapacitor Electrode in Different Alkaline Media

Transition-metal oxide has been identified as an auspicious material for supercapacitors due to its exceptional capacity. The inadequate electrochemical characteristics, such as prolonged cycle stability, can be ascribed to factors, such as low electrical conductivity, sluggish reaction kinetics, and a deficiency of active sites. The transition-metal oxides derived from the MOF materials offer a larger surface area with enriched active sites and a faster reaction rate along with good electrical conductivity. The manganese (Mn)-based metal-organic framework (MOF)-derived materials were produced using the pyrolysis method. Zeolitic imidazolate frameworks (ZIF-67) were fabricated in water at ambient temperature with the aid of triethylamine. Multiple techniques were used to examine the characteristics of the fabricated electrode materials. The influence of the electrolyte on the electrochemical activity of the Mn3O4@N-doped C electrode materials was determined in KOH, NaOH, and LiOH. For manufacturing of "Mn3O4@N-doped C", ZIF-67 was used as a precursor. The capacitive performance of the Mn3O4@N-doped C electrode increased as a result of nitrogen-doped carbon; after 5000th cycles, the electrode retained an excellent rate capability and a high specific capacitance (Cs) of 980 F g-1 at 1 A g-1 under 2.0 KOH electrolyte in a three electrode system. The carbonized manganese oxide displays also had a high Cs of 686 F g-1 in two electrode systems in 2.0 M KOH. Materials made from MOFs show promise as capacitive materials for applications in energy conversion storage owing to their straightforward synthesis and strong electrochemical performance.

Binder-Free MOF-Based and MOF-Derived Nanoarrays for Flexible Electrochemical Energy Storage: Progress and Perspectives

The fast development of Internet of Things and the rapid advent of next-generation versatile wearable electronics require cost-effective and highly-efficient electroactive materials for flexible electrochemical energy storage devices. Among various electroactive materials, binder-free nanostructured arrays have attracted widespread attention. Featured with growing on a conductive and flexible substrate without using inactive and insulating binders, binder-free 3D nanoarray electrodes facilitate fast electron/ion transportation and rapid reaction kinetics with more exposed active sites, maintain structure integrity of electrodes even under bending or twisted conditions, readily release generated joule heat during charge/discharge cycles and achieve enhanced gravimetric capacity of the whole device. Binder-free metal-organic framework (MOF) nanoarrays and/or MOF-derived nanoarrays with high surface area and unique porous structure have emerged with great potential in energy storage field and been extensively exploited in recent years. In this review, common substrates used for binder-free nanoarrays are compared and discussed. Various MOF-based and MOF-derived nanoarrays, including metal oxides, sulfides, selenides, nitrides, phosphides and nitrogen-doped carbons, are surveyed and their electrochemical performance along with their applications in flexible energy storage are analyzed and overviewed. In addition, key technical issues and outlooks on future development of MOF-based and MOF-derived nanoarrays toward flexible energy storage are also offered.

Influence of ZIF-9 and ZIF-12 structure on the formation of a series of new Co/N-doped porous carbon composites as anode electrodes for high-performance lithium-ion batteries

A series of new Co/N-doped porous carbon composites, denoted as Co/CZIF-9 and Co/CZIF-12, containing Co nanoparticles encapsulated in nitrogen-doped carbon matrices were prepared by annealing Co-based zeolite imidazolate framework materials, ZIF-9 and ZIF-12, as the efficient precursors at different temperatures. The structural features of the as-synthesized composites at 900 °C were determined by analytical methods with high reliability. Consequently, Co/CZIF-12_900 exhibits a high first specific discharge capacity of 971.0 mA h g^-1 at a current density of 0.1 A g^-1. Notably, the specific discharge/charge capacity of Co/CZIF-12_900 reaches about 508.8 mA h g^-1 at 0.1 A g^-1 after 100 cycles. The outstanding behaviors can be accounted for by the efficient incorporation of hetero-nitrogen doping and the Co nanoparticles within the layered structure of porous carbon, enhancing electrical conductivity and structural stability and limiting volume change during the intercalation/deintercalation of Li⁺ ions. These findings suggest that the Co/CZIF-12_900 material could be employed as a promising anode electrode for energy storage products.

CoSe nanoparticles in-situ grown in 3D honeycomb carbon for high-performance lithium storage

Although transition metal selenides are considered to be extremely promising anode materials for lithium-ion batteries (LIBs), severe volume changes and low electronic conductivity are their huge and unavoidable challenges. To solve these problems, CoSe nanoparticles in-situ grown on the inner surface of every macropore of 3D honeycomb C is successfully synthesized by three simple steps: dense assembling of polystyrene spheres, calcination and gaseous selenylation. The sizes of CoSe and honeycomb pores are 10-15 nm and 190 nm, respectively. The content of CoSe is 72 wt%. This unique architecture guarantees high electrochemical activity, rapid reaction kinetics and excellent structural stability of CoSe, as identified by cycling and rate performance measurements, various electrochemical kinetics analyses and ex-situ characterization of the cycled electrode material. As a result, the CoSe@honeycomb C anode exhibits extraordinary cycling performance (823.5 mAh g^-1 after 200 cycles at 0.5 A g^-1, 610.1 mAh g^-1 after 250 cycles at 2 A g^-1, 247 mAh g^-1 after 1500 cycles at 5 A g^-1) and exceptional rate capability (261.9 mAh g^-1 at 10 A g^-1, 1491.4 mAh g^-1 at 0.1 A g^-1), demonstrating that it is a potential anode material for high-performance LIBs.

ZIF-67-derived CoP/NC effectively supported Pt nanoparticles for methanol oxidation reaction

Metal-support interaction plays an important role in the catalysis reaction, and an effective support is highly desired in the hybrid catalyst construction. Herein, we demonstrated an effective catalyst system by coupling Pt nanoparticles over the ZIF-67-derived CoP/NC support for methanol oxidation reaction (MOR) in acidic and alkaline solutions. The results indicated that the Pt-CoP/NC catalyst showed high catalytic activity and stability for MOR owing to the oxophilic properties of CoP and the strong metal-support interaction, as well supported by the electrochemical measurements and the spectroscopic analysis, which far exceeded that of the Pt-Co/NC and commercial Pt/C catalysts. Specifically, the forward peak current density of the Pt-CoP/NC catalyst was 74.2 mA cm^-2 for MOR in an acidic electrolyte, which was 2.2 times higher than that of a commercial Pt/C catalyst. Further, in an alkaline electrolyte, the Pt-CoP/NC catalyst showed the highest forward peak current density of 118.6 mA cm^-2, which was 4.5 times higher than that of a commercial Pt/C catalyst. High catalytic kinetics and stability for MOR were also carefully discussed. Moreover, the Pt-CoP/NC catalyst exhibited excellent anti-poisoning ability in comparison to the Pt-Co/NC and commercial Pt/C catalysts with the help of the CO-stripping technique. The current work would be instructive for high-performance catalyst system construction based on the ZIF-67-derived CoP/NC support.

Hollow Porous N and Co Dual-Doped Silicon@Carbon Nanocube Derived by ZnCo-Bimetallic Metal-Organic Framework toward Advanced Lithium-Ion Battery Anodes

Silicon (Si) has been recognized as a promising alternative to graphite anode materials for advanced lithium-ion batteries (LIBs) owing to its superior theoretical capacity and low discharge voltage. However, Si-based anodes undergo structural pulverization during cycling due to the large volume expansion (ca. 300-400%) and continuous formation of an unstable solid electrolyte interphase (SEI), resulting in fast capacity fading. To address this challenge, a series of different amounts of silicon nanoparticles (Si NPs)-encapsulated hollow porous N-doped/Co-incorporated carbon nanocubes (denoted as p-CoNC@SiX, where X = 50, 80, and 100) as anode materials for LIBs are reported in this paper. These hollow nanocubic materials were derived by facile annealing of different contents of Si NPs-encapsulated Zn/Co-bimetallic zeolitic imidazolate frameworks (ZIF@Si) as self-sacrificial templates. Owing to the advantages of well-defined hollow framework clusters and highly conductive hollow carbon frameworks, the hollow porous p-CoNC@SiX significantly improved the electronic conductivity and Li⁺ diffusion coefficient by an order of magnitude higher than that of Si NPs. The as-prepared p-CoNC@Si80 with 80 wt % Si NPs delivered a continuously increasing specific capacity of 1008 mAh g^-1 at 500 mA g^-1 over 500 cycles, excellent reversible capacity (∼1361 mAh g^-1 at 0.1 A g^-1), and superior rate capability (∼603 mAh g^-1 at 3 A g^-1) along with an unprecedented long-life cyclic stability of ∼1218 mAh g^-1 at 1 A g^-1 over 1000 cycles caused by low volume expansion (9.92%) and suppressed SEI side reactions. These findings provide new insights into the development of highly reversible Si-based anode materials for advanced LIBs.

Uniform In Situ Grown ZIF-L Layer for Suppressing Hydrogen Evolution and Homogenizing Zn Deposition in Aqueous Zn-Ion Batteries

The hydrogen evolution and dendrite of Zn anode are the major troubles hindering the commercialization of aqueous Zn-ion batteries (AZIBs). ZIF-Ls, a typical metal-organic framework (MOF) with a highly ordered structure and abundant functional groups, seem to be the answer for the above bottlenecks. In this paper, a uniform ZIF-L layer was obtained on the Zn surface (Zn@ZIF-L) via an in situ synthesis method to moderate the solvation structure of solid-liquid interface electrolyte reducing the contact between water and Zn, thereby relieving the hydrogen evolution and corrosion. Furthermore, density functional theory (DFT) analysis reveals the binding energy of H (-4.01 eV) and Zn (-0.82 eV) for ZIF-L is superior to that of pure Zn (H (-1.49 eV) and Zn (-0.68 eV)). Due to the multifunctional ZIF-L layer, the Zn@ZIF-L can regulate Zn deposition to overcome the dendrite for obtaining a long-life Zn anode. Consequently, the modified Zn@ZIF-L anode can cycle for 800 h at 0.25 mA cm^-2 for 0.25 mAh cm^-2, while the bare Zn anode is only maintained for 422 h. Finally, a designed V₂O₅ grown on carbon cloth (V₂O₅@CC) was used as the cathode and coupled with the Zn@ZIF-L anode to assemble the full-cell. The Zn@ZIF-L//V₂O₅@CC full-cell possesses a capacity retention rate of 84.9% after 250 cycles at 0.5 C, prominently higher than Zn//V₂O₅@CC (40.7%).

Facile Synthesis of CoSe/Co3O4-CNTs/NF Composite Electrode for High-Performance Asymmetric Supercapacitor

Electrode materials are key factors for supercapacitors to endow them with excellent electrochemical properties. Here, a novel hybrid structure of a CoSe/Co₃O₄-CNTs binder free composite electrode on nickel foam was prepared via a facile flame method, followed by an electrodeposition process. Benefitting from the synergetic effects of the multicomponent (with low resistances of 1.542 Ω cm² and a moderate mesoporous size of 3.12 nm) and the enlarged specific surface area of the composite material (77.4 m² g^-1), the CoSe/Co₃O₄-CNTs composite electrode delivers a high specific capacitance of 2906 F g^-1 at 5 mV s^-1 with an excellent rate stability. The fabricated CoSe/Co3O4-CNTs/NF//AC ASC exhibits a high energy density of 43.4 Wh kg^-1 at 0.8 kW kg^-1 and a long cycle life (92.7% capacitance retention after 10,000 cycles).

Electrochemical performance of CoSe2 with mixed phases decorated with N-doped rGO in potassium-ion batteries

Potassium-ion batteries (PIBs) have received much attention as next-generation energy storage systems because of their abundance, low cost, and slightly lower standard redox potential than lithium-ion batteries (LIBs). Nevertheless, they still face great challenges in the design of the best electrode materials for applications. Herein, we have successfully synthesized nano-sized CoSe₂ encapsulated by N-doped reduced graphene oxide (denoted as CoSe₂@N-rGO) by a direct one-step hydrothermal method, including both orthorhombic and cubic CoSe₂ phases. The CoSe₂@N-rGO anodes exhibit a high reversible capacity of 599.3 mA h g⁻¹ at 0.05 A g⁻¹ in the initial cycle, and in particular, they also exhibit a cycling stability of 421 mA h g⁻¹ after 100 cycles at 0.2 A g⁻¹. Density functional theory (DFT) calculations show that CoSe₂ with N-doped carbon can greatly accelerate electron transfer and enhance the rate performance. In addition, the intrinsic causes of the higher electrochemical performance of orthorhombic CoSe₂ than that of cubic CoSe₂ are also discussed.

Potassium-ion batteries (PIBs) have received much attention as next-generation energy storage systems because of their abundance, low cost, and slightly lower standard redox potential than lithium-ion batteries (LIBs).

Hierarchical hollow superstructure cobalt selenide bird nests for high-performance lithium storage

The inferior cycling performance caused by large volume variation is the main problem that restricts the application of cobalt selenides in lithium-ion batteries. Herein, we synthesize raspberry-like Co-ethylene glycol precursor. It is further selenized into the hierarchical hollow superstructure CoSe₂/CoSe bird nests that are assembled by the hollow nanosphere units of CoSe₂ and CoSe nanocrystalline. CoSe₂/CoSe bird nests achieve excellent cycling performance, high reversible capacity and satisfactory rate capability (1361 mAh/g at 1 A/g after 1000 cycles, 579 mAh/g at 2 A/g after 2000 cycles, 315 mAh/g at 5 A/g after 1000 cycles). Electrochemical kinetics analyses and ex-situ material characterization reveal that the surface capacitive behavior controls the electrochemical reaction, and the composite has low reaction impedance, fast and stable Li⁺ diffusion, and superior structural stability. The superior lithium storage performance is attributed to the unique superstructure bird nest. Large specific surface area, abundant hierarchical pores and the opening mouth result in high electrochemical activity, which induces high reversible capacity. The small hollow nanosphere units, the sufficiently thick hierarchical porous superstructure shell and the large hollow interior bring about the strong synergistic effect to improve cycling performance. The intimately coupling of CoSe₂/CoSe nanocrystalline and the hollow nanosphere units guarantees high conductivity. This work has greatly enriched the understanding of structure design of high-performance cobalt selenide anodes.

Fabrication of CoSe@NC nanocubes for high performance potassium ion batteries

Potassium-ion batteries (PIBs) are considered as a promising candidate for large-scale energy storage. While exploring suitable anode materials are of vital need for the practical applications of PIBs. Herein, a well-designed heterostructured anode material CoSe nanocubes wrapped by N-doped carbon (CoSe@NC), has been successfully fabricated by simple annealing ZIF-67 nanocubes followed by in-situ selenization process. It is noted that ZIF-67 nanocubes are used as an effective template for the formation of porous structure, which can facilitate the construction of heterogeneous interface between CoSe and N-doped carbon (NC), effectively stabilizing CoSe with conversion reaction product Co⁰, increasing the diffusion mobility of electrons and K⁺-ions, and alleviating huge volume change. As expected, the heterostructured CoSe@NC nanocubes exhibit excellent K⁺-storage performance, which can display a rather high initial charge capacity (388.7 mAh g^-1 at 0.1 A g^-1 with the columbic efficiency of 70%), superior cyclic stability (309.6 mA h g^-1 after 500 cycles at 2 A g^-1), and exceptional rate capability (365.9 mAh g^-1 at 2 A g^-1). In terms of the low-cost and facile production approach for CoSe@NC, which makes the CoSe@NC a promising anode material for PIBs.

Simultaneously enhancing redox kinetics and inhibiting the polysulfide shuttle effect using MOF-derived CoSe hollow sphere structures for advanced Li-S batteries

Lithium-sulfur (Li-S) batteries generally suffer from a serious "shuttle effect" during the charging/discharging process, resulting in the loss of active components and sluggish redox reaction kinetics that hinder the cycle life and rate performance of the battery. To address this, CoSe/C hollow structures (CoSe/C HSs) were prepared via a simple hydrothermal strategy and used as a sulfur host for Li-S batteries. The battery with CoSe/C HSs exhibited a high initial specific discharge capacity of 1405 mA h g-1 with a coulombic efficiency of 99.8% at 0.1C. Additionally, S@CoSe/C HS cathodes with a high sulfur loading of 5.1 mg cm-2 delivered a considerable specific discharge capacity of 1256.1 mA h g-1 and maintained a high capacity of 1120 mA h g-1 after 100 cycles with a capacity decay rate of 0.11% per cycle at 0.1C. The unique raspberry-like structure of CoSe/C HSs prevents polysulfides from escaping the cathode host via both physical containment and the formation of Co-S and Se-Li chemical bonds, and it also enhances the polysulfide redox kinetics. Furthermore, the peculiar raspberry-like structure can withstand volume changes during charging/discharging to better protect the cathode.

An energy efficient bi-functional electrode for continuous cation-selective capacitive deionization

Effective ion intercalation nanomaterials provide tremendous opportunities to various deionization systems such as capacitive deionization (CDI) to significantly improve the removal capacity of brackish water desalination. However, the asymmetric design of CDI devices causes a low removal rate due to the indispensable regeneration half-cycle. Furthermore, choices of chloride selective electrodes for such devices are limited. This imposes a big challenge on further improvement of CDI systems. Herein, we report a cation-selective CDI system using a single bi-functional Na2VTi(PO4)3@carbon nanomaterial with redox couples of V4+/V3+ and Ti3+/Ti4+ as an advanced symmetric electrode. The as-prepared continuous desalination set-up shows a superior removal rate of 0.022 mg g-1 s-1 (1.32 mg g-1 min-1) with a high half-cycle removal capacity of 35 mg g-1, and extremely low energy consumption of 0.14 W h g-1 (at a current density of 100 mA g-1). In addition, an extremely high cycle-stability of at least 50 cycles is achieved. The bi-functional intercalation mechanism is investigated by in situ XRD and ex situ XPS. The symmetric device yields a simplified and low-cost configuration with improved energy efficiency and high removal capacity. This opens a new horizon towards the commercialization of CDI technologies.

Hierarchical 3D Oxygenated Cobalt Molybdenum Selenide Nanosheets as Robust Trifunctional Catalyst for Water Splitting and Zinc-Air Batteries

The development of hierarchical nanostructures with highly active and durable multifunctional catalysts has a new significance in the context of new energy technologies of water splitting and metal-air batteries. Herein, a strategy is demonstrated to construct a 3D hierarchical oxygenated cobalt molybdenum selenide (O-Co_{1- x} Mo_x Se₂ ) series with attractive nanoarchitectures, which are fabricated by a simple and cost-effective hydrothermal process followed by an exclusive ion-exchange process. Owing to its highly electroactive sites with numerous nanoporous networks and plentiful oxygen vacancies, the optimal O-Co_0.5 Mo_0.5 Se₂ could catalyze the hydrogen evolution reaction and oxygen evolution reaction effectively with a low overpotential of ≈102 and 189 mV, at a current density of 10 mA cm^-2 , respectively, and exceptional durability. Most importantly, the O-Co_0.5 Mo_0.5 Se₂ ||O-Co_0.5 Mo_0.5 Se₂ water splitting device only entails a voltage of ≈1.53 V at a current density of 10 mA cm^-2 , which is much better than benchmark Pt/C||RuO₂ (≈1.56 V). Furthermore, O-Co_0.5 Mo_0.5 Se₂ air cathode-based zinc-air batteries exhibit an excellent power density of 120.28 mW cm^-2 and exceptional cycling stability for 60 h, superior to those of state-of-art Pt/C+RuO₂ pair-based zinc-air batteries. The present study provides a strategy to design hierarchical 3D oxygenated bimetallic selenide-based multifunctional catalysts for energy conversion and storage systems.