Ultralow nitrogen-doped carbon coupled carbon-doped Co3O4 microrods with tunable electron configurations for advanced Li-storage properties

Phase-Dependent Electrochemical Performance of CoxSy (x = 1,9; y = 2,8) for Symmetric Supercapacitor Application

Modulating the oxidation states of transition metal species is a practical approach to enhance redox activity and increase the number of active sites in electrode materials. Herein, we describe a simple one-step hydrothermal approach to prepare CoxSy with two different phases, cobalt pyrite (CoS2) and cobalt pentlandite (Co9S8), to explain the influence of material microstructure and properties on electrochemical performance. The as-prepared CoS2 and Co9S8 were investigated as symmetric supercapacitor (SC) devices for potential energy storage applications. Co9S8 exhibited the highest specific gravimetric capacitance of 14.12 Fg-1 at 0.2 mAcm-2 with capacitance retention of 91.3% after 10,000 cycles, indicating robust cycling stability. In addition, the Co9S8 SC device showed the highest energy (E) and power (P) density of 9.14 Whkg-1 and 0.23 kWkg-1. These results highlight a simple approach of tailoring different phase syntheses of CoxSy structure toward high-performance electrode material for energy storage and conversion.

Evaluation of the effect of precursor ratios on the electrochemical performances of binder-free NiMn-phosphate electrodes for supercapattery

Binary metal phosphate electrodes have been widely studied for energy storage applications due to the synergistic effects of two different transition elements that able to provide better conductivity and stability. Herein, the battery-type binder-free nickel-manganese phosphate (NiMn-phosphate) electrodes were fabricated with different Ni:Mn precursor ratios via microwave-assisted hydrothermal technique for 5 min at 90 °C. Overall, NiMn3P electrode (Ni:Mn = 1:3) showed an outstanding electrochemical performance, displaying the highest specific (areal) capacity at 3 A/g of 1262.4 C/g (0.44 C/cm2), and the smallest charge transfer resistance of 108.8 Ω. The enhanced performance of NiMn3P electrode can be ascribed to the fully grown amorphous nature and small-sized flake and flower structures of NiMn3P electrode material on the nickel foam (NF) surface. This configuration offered a higher number of active sites and a larger exposed area, facilitating efficient electrochemical reactions with the electrolyte. Consequently, the NiMn3P//AC electrode combination was chosen to further investigate its performance in supercapattery. The NiMn3P//AC supercapattery exhibited remarkable energy density of 105.4 Wh/kg and excellent cyclic stability with 84.7% retention after 3000 cycles. These findings underscored the superior electrochemical performance of the battery-type binder-free NiMn3P electrode, and highlight its potential for enhancing the overall performance of supercapattery.

Electrocatalytic Mechanism of Defect in Spinels for Water and Organics Oxidation

Spinels display promising electrocatalytic ability for oxygen evolution reaction (OER) and organics oxidation reaction because of flexible structure, tunable component, and multifold valence. Unfortunately, limited exposure of active sites, poor electronic conductivity, and low intrinsic ability make the electrocatalytic performance of spinels unsatisfactory. Defect engineering is an effective method to enhance the intrinsic ability of electrocatalysts. Herein, the recent advances in defect spinels for OER and organics electrooxidation are reviewed. The defect types that exist in spinels are first introduced. Then the catalytic mechanism and dynamic evolution of defect spinels during the electrochemical process are summarized in detail. Finally, the challenges of defect spinel electrocatalysts are brought up. This review aims to deepen the understanding about the role and evolution of defects in spinel for electrochemical water/organics oxidation and provide a significant reference for the design of efficient defect spinel electrocatalysts.

A Review of Cobalt-Containing Nanomaterials, Carbon Nanomaterials and Their Composites in Preparation Methods and Application

With the increasing demand for sustainable and green energy, electric energy storage technologies have received enough attention and extensive research. Among them, Li-ion batteries (LIBs) are widely used because of their excellent performance, but in practical applications, the electrochemical performance of electrode materials is not satisfactory. Carbon-based materials with high chemical stability, strong conductivity, high specific surface area, and good capacity retention are traditional anode materials in electrochemical energy storage devices, while cobalt-based nano-materials have been widely used in LIBs anodes because of their high theoretical specific capacity. This paper gives a systematic summary of the state of research of cobalt-containing nanomaterials, carbon nanomaterials, and their composites in LIBs anodes. Moreover, the preparation methods of electrode materials and measures to improve electrochemical performance are also summarized. The electrochemical performance of anode materials can be significantly improved by compounding carbon nanomaterials with cobalt nanomaterials. Composite materials have better electrical conductivity, as well as higher cycle ability and reversibility than single materials, and the synergistic effect between them can explain this phenomenon. In addition, the electrochemical performance of materials can be significantly improved by adjusting the microstructure of materials (especially preparing them into porous structures). Among the different microscopic morphologies of materials, porous structure can provide more positions for chimerism of lithium ions, shorten the diffusion distance between electrons and ions, and thus promote the transfer of lithium ions and the diffusion of electrolytes.

High-Entropy Oxide for Highly Efficient Luminol-Dissolved Oxygen Electrochemiluminescence and Biosensing Applications

The luminol-dissolved O₂ (DO) electrochemiluminescence (ECL) sensing system has recently gained growing interest; however, the drawback of the ultra-low ECL signal response greatly hinders its potential quantitative applications. In this work, for the first time, we explored the use of high entropy oxide (HEO) comprising five metal ingredients (Ni, Co, Cr, Cu, and Fe), to accelerate the reduction reaction of DO into reactive oxygen species (ROS) for boosting the ECL performance of the luminol-DO system. Benefiting from the existing abundant oxygen vacancies induced by the unique crystal structure of the HEO, DO could be efficiently converted into ROS, thus significantly boosting the performance of the corresponding ECL sensor (with an ∼240-fold signal enhancement in this study). As a proof of concept, under optimal conditions, the developed HEO-involved luminol-DO ECL sensing system was successfully applied for efficient biosensing of dopamine and alkaline phosphatase with a fine linear range from 1 pM to 10 nM and from 0.01 to 100 U/L as well as a low limit of detection of 5.2 pM and 0.008 U/L, respectively.

Highly efficient Co3O4/CeO2 heterostructure as anode for lithium-ion batteries

Co₃O₄ has been extensively studied as an anode material for lithium-ion batteries (LIBs) because of its high theoretical capacity. However, during the charging-discharging processes, the issues of large volume change and low electric conductivity arise, which significantly limit the practical applications of Co₃O₄. To solve these issues, a Co₃O₄/CeO₂ heterostructure derived from metal-organic frameworks (MOFs) was designed and synthesized through one-step microwave synthesis. Benefiting from the mesoporous structure and presence of hetero-components, Co₃O₄/CeO₂ having the molar ratio of Co/Ce = 5:1 (denoted as 5Co₃O₄/CeO₂) exhibits high reversible capacity and excellent cycling stability when used as an anode material for LIBs. Specifically, compared to a single-phase Co₃O₄ anode, which shows a capacity of 538.6 mAh/g after 100 cycles, 5Co₃O₄/CeO₂ exhibits a higher capacity (1131.2 mAh/g at 100 mA/g). This study provides a novel strategy for using rare earth components to modify electrode materials.

Copper niobate nanowires immobilized on reduced graphene oxide nanosheets as rate capability anode for lithium ion capacitor

Binary metal niobium oxides can offer a higher specific capacity compared to niobium pentoxide (Nb₂O₅) and thus are ideal anode candidates for lithium ion capacitors (LICs). However, their lower electronic conductivity limits their ability to achieve high energy and power densities. In this paper, one-dimensional (1D) copper niobate (CuNb₂O₆) nanowires are successfully prepared by electrospinning technology and then immobilized on two-dimensional (2D) reduced graphene oxide (rGO) nanosheets to form a unique 1D nanowire/2D nanosheet CuNb₂O₆/rGO structure. The 1D/2D CuNb₂O₆/rGO electrode exhibits a high specific capacity of 312.2 mAh g^-1 at 100 mA g^-1 as the anode of LICs. The proposed Li⁺ storage mechanism of the CuNb₂O₆ anode involves CuNb₂O₆ decomposition into lithium niobate (Li₃NbO₄) and copper (Cu) during the initial lithium insertion process. The intercalation-type Li₃NbO₄ will further serve as the host to Li⁺ and the inactive Cu phase will act as a conductive network for electron transportation. Furthermore, the energy density of the assembled CuNb₂O₆/rGO//activated carbon (CuNb₂O₆/rGO//AC) device could achieve a value as high as 92.1 Wh kg^-1 and could thus be considered as a possible alternative electrode material for high energy and power LICs.

Self-Templating Synthesis of Hollow Co3O4 Nanoparticles Embedded in N,S-Dual-Doped Reduced Graphene Oxide for Lithium Ion Batteries

The design and synthesis of hollow-nanostructured transition metal oxide-based anodes is of great importance for long-term operation of lithium ion batteries. Herein, we report a two-step calcination strategy to fabricate hollow Co₃O₄ nanoparticles embedded in a N,S-co-doped reduced graphene oxide framework. In the first step, core-shell-like Co@Co₃O₄ embedded in N,S-co-doped reduced graphene oxide is synthesized by pyrolysis of a Co-based metal organic framework/graphene oxide precursor in an inert atmosphere at 800 °C. The designed hollow Co₃O₄ nanoparticles with an average particle size of 25 nm and wall thickness of about 4-5 nm are formed by a further calcination process in air at 250 °C via the nanoscale Kirkendall effect. Both micropores and mesopores are generated in the HoCo₃O₄/NS-RGO framework. Benefiting from the hierarchical porous structure of the hollow Co₃O₄ and the co-doping of nitrogen and sulfur atoms in reduced graphene oxide, the thus-assembled battery exhibits a high specific capacity of 1590 mAh g^-1 after 600 charge-discharge cycles at 1 A g^-1 and a promising rate performance from 0.2 to 10 A g^-1.