Graphene Matrix Sheathed Metal Vanadate Porous Nanospheres for Enhanced Longevity and High-Rate Energy Storage Devices

In-situ precipitation zero-valent Co on Co2VO4 to activate oxygen vacancies and enhance bimetallic ions redox for efficient detection toward Hg(II)

Despite the widespread utilization of variable valence metals in electrochemistry, it is still a formidable challenge to enhance the valence conversion efficiency to achieve excellent catalytic activity without introducing heterophase elements. Herein, the in-situ precipitation of Co particles on Co2VO4 not only enhanced the concentration of oxygen vacancies (Ov) but also generated a greater number of low-valence metals, thereby enabling efficient reduction towards Hg(II). The electroanalysis results demonstrate that the sensitivity of Co/Co2VO4 towards Hg(II) was measured at an impressive value of 1987.74 μA μM-1 cm-2, significantly surpassing previously reported results. Further research reveals that Ov acted as the main adsorption site to capture Hg(II). The redox reactions of Co2+/Co3+ and V3+/V4+ played a synergistic role in the reduction of Hg(II), accompanied by the continuous supply of electrons from zero-valent Co to expedite the valence cycle. The Co/Co2VO4/GCE presented remarkable selectivity towards Hg(II), with excellent stability, reproducibility, and anti-interference capability. The electrode also exhibited minimal sensitivity fluctuations towards Hg(II) in real water samples, underscoring its practicality for environmental applications. This study elucidates the mechanism underlying the surface redox reaction of metal oxides facilitated by zero-valent metals, providing us with new strategies for further design of efficient and practical sensors.

Oxygenated copper vanadium selenide composite nanostructures as a cathode material for zinc-ion batteries with high stability up to 10 000 cycles

The development of aqueous zinc-ion batteries (AZiBs) towards practical implementations is hampered by unsuitable host cathode materials. Herein, we reported a high-capacity, stable, and long-cycle-life (10 000 cycles) oxygenated copper vanadium selenide composite material (Cu_0.59V₂O₅/Cu_0.828V₂O₅@Cu_1.8Se₁/Cu₃Se₂, denoted as O-CuVSe) as a cathode for AZiBs. The newly constructed O-CuVSe composite cathode can be operated in the wide potential window of 0.4-2.0 V, exhibiting a high specific capacity of 154 mA h g^-1 at 0.2 A g^-1 over 100 cycles. Interestingly, the O-CuVSe composite cathode delivered excellent specific capacities of 117 and 101.4 mA h g^-1 over 1000 cycles at 1 and 2 A g^-1, respectively. Even at a high current density of 5 A g^-1, the cathode delivered a high reversible capacity of 74.5 mA h g^-1 over an ultra-long cycling life of 10 000 cycles with no obvious capacity fading. Apart from this, the cathode exhibited excellent rate capability at different current densities. The superior electrochemical properties originate from the synergistic effects between the oxygen vacancy engineering and interlayer doping of Cu ions to increase the structural stability during the cycling, enhancing the electron/ion transport kinetics. Moreover, the Zn²⁺ storage mechanism in the Zn/O-CuVSe aqueous rechargeable battery was explored. This study provides a new opportunity for the fabrication of different kinds of a new class of cathode materials for high-voltage and high-capacity AZiBs and other energy storage devices.

ZIF-67 Derived Co2VO4 Hollow Nanocubes for High Performance Asymmetric Supercapacitors

In this work, a new type of Co₂VO₄ hollow nanocube (CoVO-HNC) was synthesized through an ion exchange process using ZIF-67 nanocubes as a template. The hollow nanocubic structure of the CoVO-HNC provides an abundance of redox sites and shortens the ion/electron diffusion path. As the electrode material of supercapacitors, the specific capacitance of CoVO-HNC is 427.64 F g⁻¹ at 1.0 A g⁻¹. Furthermore, an asymmetric supercapacitor (ASC) was assembled using CoVO-HNC and activated carbon (AC) as electrodes. The ASC device attains an energy density of 25.28 Wh kg⁻¹ at a high-power density of 801.24 W kg⁻¹, with 78% capacitance retention after 10,000 cycles at 10 A g⁻¹.

Core-Shell Co2VO4/Carbon Composite Anode for Highly Stable and Fast-Charging Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are promising candidates for large-scale energy storage systems due to the abundance and wide distribution of sodium resources. Various solutions have been successfully applied to revolve the large-ion-size-induced battery issues at the mid-to-low current density range. However, the fast-charging properties of SIBs are still in high demand to accommodate the increasing energy needs at large to grid scales. Herein, a core-shell Co₂VO₄/carbon composite anode is designed to tackle the fast-charging problem of SIBs. The synergetic effect from the stable spinel structure of Co₂VO₄, the size of the nanospheres, and the carbon shell provide enhanced Na⁺ ion diffusion and electron transfer rates and outstanding electrochemical performance. With an ultrahigh current density of 5 A g^-1, the Co₂VO₄@C anode achieved a capacity of 135.1 mAh g^-1 and a >98% capacity retention after 2000 cycles through a pseudocapacitive dominant process. This study provides insights for SIB fast-charging material design and other battery systems such as lithium-ion batteries.

Enhancing Co/Co2VO4 Li-ion battery anode performances via 2D-2D heterostructure engineering

High-capacity Co₂VO₄ has become a potential anode material for lithium-ion batteries (LIBs), benefiting from its lower output voltage during cycling than other cobalt vanadates. However, the application of this new conversion-type electrode is still hampered by its inherent large volume variation and poor kinetics. Here, a 2D-2D heterostructure building strategy has been developed to enhance the electrode performance of Co₂VO₄ through construction of Co/Co₂VO₄ nanocomposites converted from the in situ phase separation of Co₂V₂O₇·3.3H₂O nanosheets. Co/Co₂VO₄ based on face-to-face contact exhibits the optimized stacking configuration, where Co nanocrystals give gaps of several nanometers between stacked Co₂VO₄ nanosheets, enabling full contact with the electrolyte, a shorter transport path of lithium ions and more reactive sites. With this design, Co/Co₂VO₄ anodes deliver outstanding reversible capacity (750 mA h g^-1 at 1 A g^-1) with ultrahigh capacity retention rate, and excellent cycle stability at high rate (520 mA h g^-1 at 5 A g^-1 retained after 400 cycles). An "active center's charge transfer-capacity compensation" model was proposed based on capacity analysis, XPS depth analysis and HRTEM observation to uncover the fundamental reason of the excellent cycle performance. This in situ 2D-2D heterostructure constructing strategy may open up the possibility for designing high-performance LIBs.

Novel Conductive Ag-Decorated NiFe Mixed Metal Telluride Hierarchical Nanorods for High-Performance Hybrid Supercapacitors

Mixed metal chalcogenide nanoarchitectures have been attracting enormous attention as battery-type electrodes for hybrid supercapacitors (HSCs) owing to their enhanced electrochemical (EC) performance. Despite having high electrical conductivity and good EC properties, tellurium has not been fully utilized in metal chalcogenide electrodes as much as sulfur and selenium. Herein, a facile strategy for the fabrication of nickel and iron (NiFe) mixed metal telluride hierarchical nanorods (MMT HNRs) on nickel foam (NF) is proposed. Furthermore, conductive silver (Ag) is decorated on MMT HNRs (AMMT HNRs) to improve the conducting channels, thereby EC performance. Benefitting from the combined advantages of electroactive NiFe mixed metal, conductive tellurium and Ag, and hierarchical nanorod-like nanomorphology, the AMMT HNR electrode has delivered high areal capacity (1.1 mAh cm^-2). Finally, the AMMT based HSC with activated carbon coated NF (AC/NF) as a negative electrode exhibited the highest areal capacitance (1176.5 mF cm^-2) with high areal energy density (0.669 mWh cm^-2) and power density (64 mW cm^-2). Moreover, the HSC device has maintained good cycling stability (86% capacity retention) even after 5000 cycles. New findings of this study definitely shed light on the development of telluride-based mixed metal chalcogenide supercapacitors.

Preparation of NiO decorated CNT/ZnO core-shell hybrid nanocomposites with the aid of ultrasonication for enhancing the performance of hybrid supercapacitors

Supercapacitor (SC) electrodes fabricated with the combination of carbon nanotubes (CNTs) and metal oxides are showing remarkable advancements in the electrochemical properties. Herein, NiO decorated CNT/ZnO core-shell hybrid nanocomposites (CNT/ZnO/NiO HNCs) are facilely synthesized by a two-step solution-based technique for the utilization in hybrid supercapacitors. Benefitting from the synergistic advantages of three materials, the CNT/ZnO/NiO HNCs based electrode has evinced superior areal capacity of ~67 µAh cm-2 at a current density of 3 mA cm-2 with an exceptional cycling stability of 112% even after 3000 cycles of continuous operation. Highly conductive CNTs and electrochemically active ZnO contribute to the performance enhancement. Moreover, the decoration of NiO on the surface of CNT/ZnO core-shell increases the electro active sites and stimulates the faster redox reactions which play a vital role in augmenting the electrochemical properties. Making the use of high areal capacity and ultra-long stability, a hybrid supercapacitor (HSC) was assembled with CNT/ZnO/NiO HNCs coated nickel foam (CNT/ZnO/NiO HNCs/NF) as positive electrode and CNTs coated NF as negative electrode. The fabricated HSC delivered an areal capacitance of 287 mF cm-2 with high areal energy density (67 µWh cm-2) and power density (16.25 mW cm-2). The combination of battery type CNT/ZnO/NiO HNCs/NF and EDLC type CNT/NF helped in holding the capacity for a long period of time. Thus, the systematic assembly of CNTs and ZnO along with the NiO decoration enlarges the application window with its high rate electrochemical properties.

Metal-Organic Framework-Derived Co3 V2 O8 @CuV2 O6 Hybrid Architecture as a Multifunctional Binder-Free Electrode for Li-Ion Batteries and Hybrid Supercapacitors

Metal-organic frameworks (MOFs) are promising materials in diverse fields because of their constructive traits of varied structural topologies, high porosity, and high surface area. MOFs are also an ideal precursor/template to derive porous and functional morphologies. Herein, Co₃ V₂ O₈ nanohexagonal prisms are grafted on CuV₂ O₆ nanorod arrays (CuV-CoV)-grown copper foam (CF) using solution-processing methods, followed by thermal treatment. Direct preparation of active material on CF can potentially eliminate electrochemically inactive and non-conductive binders, leading to improved charge-transfer rate. Furthermore, solution-processing methods are simple and cost-effective. Owing to versatile valence states and good redox activity, the vanadium-incorporated mixed metal oxides (CuV-CoV) exhibited superior electrochemical performance in lithium (Li)-ion battery and supercapacitor (SC) studies. Furthermore, hollow carbon particles (HCPs) derived from MOF particles (MOF-HCPs) are used as the anode material in SCs. A hybrid SC (HSC) fabricated with CuV-CoV and MOF-HCP materials exhibited noteworthy electrochemical properties. Moreover, a solid-state HSC (SSHSC) is constructed and its real-time feasibility is investigated by harvesting the dynamic energy of a bicycle with the help of a direct current generator. The charged SSHSCs potentially powered various electronic components.

Synthesis of a three-dimensional cross-linked Ni-V2O5 nanomaterial in an ionic liquid for lithium-ion batteries

A three-dimensional cross-linked Ni-V₂O₅ nanomaterial with a particle size of 250-300 nm was successfully prepared in a 1-butyl-3-methylimidazole bromide ionic liquid (IL). The formation of this structure may follow the rule of dissolution-recrystallization and the ionic liquid, as both a dissolution and structure-directing agent, plays an important role in the formation of the material. After calcination of the precursor, the active material (Ni-V₂O₅-IL) was used as an anode for lithium-ion batteries. The designed anode exhibited excellent electrochemical performance with 765 mA h g^-1 at a current density of 0.3 A g^-1 after 300 cycles, which is much higher than that of a NiVO-W material prepared via a hydrothermal method (305 mA h g^-1). These results show the remarkable superiority of this novel electrode material synthesized in an ionic liquid.