Rapid activation and enhanced cycling stability of Co3O4 microspheres decorated by N-doped amorphous carbon shell for advanced LIBs

Vanadium Oxide Cathode Coinserted by Ni2+ and NH4+ for High-Performance Aqueous Zinc-Ion Batteries

Vanadium-based oxides have garnered significant attention as cathode materials for aqueous zinc-ion batteries (AZIBs) because of their high theoretical capacity and low cost. However, the limited reaction kinetics and poor long-term cycle stability hinder their widespread application. In this paper, we propose a novel approach by coinserting Ni2+ and NH4+ ions into V2O5·3H2O, i.e., NNVO. Structural characterization shows that the coinsertion of Ni2+ and NH4+ not only extends the interlayer spacing of V2O5·3H2O but also significantly promotes the transport kinetics of Zn2+ because of the synergistic "pillar" effect of Ni2+ and NH4+, as well as the increased oxygen vacancies that effectively lower the energy barrier for Zn2+ insertion. As a result, the AZIBs with an NNVO electrode exhibit a high capacity of 398.1 mAh g-1 (at 1.0 A g-1) and good cycle stability with 89.1% capacity retention even after 2000 cycles at 5.0 A g-1. At the same time, a highly competitive energy density of 262.9 Wh kg-1 is delivered at 382.9 W kg-1. Considering the simple scheme and the resultant high performance, this study may provide a positive attempt to develop high-performance AZIBs.

Binder-free barium-implanted MnO2 nanosheets on carbon cloth for flexible zinc-ion batteries

The intrinsically low electrical conductivity and poor structural fragility of MnO2 have significantly hampered the zinc storage performance. In this work, Ba2+-implanted δ-MnO2 nanosheets have been hydrothermally grown on a carbon cloth (Ba-MnO2@CC) as an extremely stable and efficient cathode material of aqueous zinc-ion batteries. The three-dimensionally porous architecture composed of interwoven thin MnO2 nanosheets effectively shortens the electron/ion transport distances, enlarges the electrode/electrolyte contact area, and increases the active sites for the electrochemical reaction. Meanwhile, Ba2+ could function as an interlayer pillar to stabilize the crystal structure of MnO2. Consequently, the as-optimized Ba-MnO2@CC exhibits remarkable Zn2+ storage capabilities, such as a high capacity (305 mAh g-1 at 0.2 A g-1), prolonged lifespan (95% retention after a 200-cycling test), and superb rate capability. The binder-free cathode is also applicable for flexible energy storage devices with attractive properties. The present investigation provides important insights into designing advanced cathode materials toward wearable electronics.

Metal Oxide Wrapped by Reduced Graphene Oxide Nanocomposites as Anode Materials for Lithium-Ion Batteries

The reduced graphene oxide/iron oxide (rGO/Fe₂O₃) and reduced graphene oxide/cobalt oxide (rGO/Co₃O₄) composite anodes have been successfully prepared through a simple and scalable ball-milling synthesis. The substantial interaction of Fe₂O₃ and Co₃O₄ with the rGO matrix strengthens the electronic conductivity and limits the volume variation during cycling in the rGO/Fe₂O₃ and rGO/Co₃O₄ composites because reduced graphene oxide (rGO) helps the metal oxides (MOs) to attain a more efficient diffusion of Li-ions and leads to high specific capacities. As anode materials for LIBs, the rGO/Fe₂O₃ and rGO/Co₃O₄ composites demonstrate overall superb electrochemical properties, especially rGO/Fe₂O₃T-5 and rGO/Co₃O₄T-5, showcasing higher reversible capacities of 1021 and 773 mAhg^-1 after 100 cycles at 100 mAg^-1, accompanied by the significant rate performance. Because of their superior electrochemical efficiency, high capacity and low cost, the rGO/Fe₂O₃ and rGO/Co₃O₄ composites made by ball milling could be outstanding anode materials for LIBs. Due to the excellent electrochemical performance, the rGO/Fe₂O₃ and rGO/Co₃O₄ composites prepared via ball milling could be promising anode materials with a high capacity and low cost for LIBs. The findings may provide shed some light on how other metal oxides wrapped by rGO can be prepared for future applications.

Excellent photocatalytic performances of Co3O4-AC nanocomposites for H2 production via wastewater splitting

Natural sunlight-driven photocatalytic hydrogen production from wastewater is one of the most desirable techniques that can realize future green energy technology. Herein, we report the synthesis and the characterization of the biomass activated carbon (AC)-decorated cobalt oxide (Co₃O₄) nanocomposites for solar-stimulated photocatalytic hydrogen production from sulphide wastewater. The Co₃O₄-AC nanocomposites were ultrasonically synthesized by using hydrothermally-grown spinel Co₃O₄ nanoflakes and biomass-derived AC nanoflakes. Co₃O₄-AC showed a nanobundle-like aggregated morphology, and exhibited a large specific surface area (~133 m²/g). Through utilizing Co₃O₄-AC as a photocatalyst for photocatalytic splitting of sulphide wastewater (0.2 M) under solar irradiance with 730 W/m², an enhanced H₂ production efficiency (~70 mL/h) was achieved owing to the synergic effects from 2-dimentionally configured Co₃O₄ and AC microstructures; i.e., large surface area of Co₃O₄ and high electrical conductivity of AC. These findings suggest the nanocomposites of Co₃O₄-AC to hold great promise for the green approach of photocatalytic wastewater splitting.

Electrospun cobalt Prussian blue analogue-derived nanofibers for oxygen reduction reaction and lithium-ion batteries

Electrospinning is an effective technique to fabricate one-dimensional materials. In this study, cobalt-embedded carbon nanofibers (Co@CNFs) are obtained via carbonization of electrospun cobalt Prussian blue analogue (Co-Co PBA) under nitrogen atmosphere. The Co@CNFs have metallic cobalt surrounded by graphitic carbon shells and possess high specific surface area, rich porosity, high graphitic degree, and rational nitrogen doping. The structure merits endow them with excellent electrocatalytic performances for oxygen reduction reaction (ORR): an onset potential of 0.867 V vs. RHE and 0.784 V vs. RHE at j =  - 3 mA cm^-2 with a four-electron transfer process. Through a further mild oxidation process, we obtain Co₃O₄ nanoparticles-embedded nitrogen-doped carbon (Co₃O₄@CNFs) with spindle-like morphology. When working as the anode materials for lithium-ion batteries (LIBs), Co₃O₄@CNFs show high specific capacity, good stability, and excellent rate capability. The Co₃O₄@CNFs anode delivers a discharge specific capacity of 1404 mA h g^-1 after 100 cycles at a current density of 100 mA g^-1 and about 500 mA h g^-1 after 500 cycles at 2000 mA g^-1. The diffusion- and capacitive-controlled processes both contribute to the charge storage of the Co₃O₄@CNFs electrode. This study provides a new strategy to fabricate the excellent electrocatalysts for ORR and anode materials for LIBs via facile electrospinning.

Hydrothermal-template synthesis and electrochemical properties of Co3O4/nitrogen-doped hemisphere-porous graphene composites with 3D heterogeneous structure

Despite the high capacity of Co₃O₄ employed in lithium-ion battery anodes, the reduced conductivity and grievous volume change of Co₃O₄ during long cycling of insertion/extraction of lithium-ions remain a challenge. Herein, an optimized nanocomposite, Co₃O₄/nitrogen-doped hemisphere-porous graphene composite (Co₃O₄/N-HPGC), is synthesized by a facile hydrothermal-template approach with polystyrene (PS) microspheres as a template. The characterization results demonstrate that Co₃O₄ nanoparticles are densely anchored onto graphene layers, nitrogen elements are successfully introduced by carbamide and the nanocomposites maintain the hemispherical porous structure. As an anode material for lithium-ion batteries, the composite material not only maintains a relatively high lithium storage capacity (the first discharge specific capacity can reach 2696 mA h g⁻¹), but also shows significantly improved rate performance (1188 mA h g⁻¹ at 0.1 A g⁻¹, 344 mA h g⁻¹ at 5 A g⁻¹) and enhanced cycling stability (683 mA h g⁻¹ after 500 cycles at 1 A g⁻¹). The enhanced electrochemical properties of Co₃O₄/N-HPGC nanocomposites can be ascribed to the synergistic effects of Co₃O₄ nanoparticles, novel hierarchical structure with hemisphere-pores and nitrogen-containing functional groups of the nanomaterials. Therefore, the developed strategy can be extended as a universal and scalable approach for integrating various metal oxides into graphene-based materials for energy storage and conversion applications.

The Co₃O₄/N-HPGC nanocomposites synthesized by a hydrothermal-template approach with polystyrene microspheres as the template possess excellent electrochemical performance.

Co3O4 hollow nanospheres/carbon-assembled mesoporous polyhedron with internal bubbles encapsulating TiO2 nanosphere for high-performance lithium ion batteries

Co₃O₄ hollow nanospheres 15 nm in the diameter were assembled to the mesoporous polyhedron together with carbon. Within the Co₃O₄ polyhedrons, the bubbles 300-500 nm in diameter were uniformly generated. Every bubble further encapsulated one TiO₂ nanosphere, forming a unique sphere-bubble structure. The specific surface area and the pore volume were calculated to be 97.85 and 0.31 cm³ g^-1. When evaluated as anode material for lithium ion batteries, the as-prepared material exhibited superior lithium storage properties with high specific capacity, excellent cycling stability and good rate capability. After 400 cycles, the discharge capacity of 609 mAh g^-1 was still delivered at current density of 335 mA g^-1. Even at a high current density of 2000 mA g^-1, the reversible capacity reached 296 mAh g^-1. The outstanding electrochemical performance was attributed to the unique hybrid structure, which avoids nanomaterial aggregation, promotes ion diffusion and electron transfer, accommodates volume change of Co₃O₄ during (de)lithiation process, enhances structure strength, cycling stability and space utilization ratio of the hollow material.

Mechanistic insights into the phenomena of increasing capacity with cycle number: using pulsed-laser deposited MoO2thin film electrodes

Thin film electrodes often feature fluctuations in capacity with cycle number. This work shows how electrode reactions and peeling off the current collector is a plausible mechanism for these fluctuations.