A novel edge-rich structure of CuO/Co3O4 derived from Prussian blue analogue as a high-rate and ultra-stable electrode for efficient capacitive storage

Colorimetric/fluorescent dual-mode assay for antioxidant capacity of gallnuts based on CuCo nanozyme and AIE luminogen

In this work, we present a dual-mode assay system consisting of a nanozyme and a luminogen with the aggregation-induced emission (AIE) feature. In the assay system, the chosen nanozyme named CuCo-0 catalyzes the substrate to produce colorimetric signals, while the aggregates of H4ETTC (4,4',4″,4‴-(ethene-1,1,2,2-tetrayl) tetrakis ([1,1'-biphenyl]-4-carboxylic acid), a typical AIE luminogen, generate fluorescent signals. The peroxidase-like activity of the CuCo-0 nanozyme can be remarkably suppressed with sequential additions of antioxidants, leading to a dual-signal response characterized by enhanced fluorescence emission and reduced UV-vis absorbance. On this basis, a dual-mode assay capable of producing both colorimetric and fluorescent signals for the assessment of antioxidant capacity using gallic acid as a representative antioxidant was exploited. Good linearity can be obtained in the 0-60 μM range for both colorimetric analysis and fluorescent analysis, with detection limits of 1.3 μM and 0.35 μM, respectively. Furthermore, this dual-mode assay was successfully applied to real gallnut samples, yielding satisfactory results.

Prussian blue analogue-derived Co3O4/Fe2O3 with a partially hollow and octahedral structure for high-performance supercapacitors

A supercapacitor (SC) is considered as a promising energy storage device because of its high power density, fast charging/discharging speed and long cycle life. The transition metal oxides prepared by traditional methods face some challenges, such as low conductivity and uncontrollable pore size distribution. Therefore, we have prepared Prussian blue analogues (PBAs) using a coprecipitation method. By adjusting additives in the experimental process, uniform PBAs with a series of regular morphologies and structures are successfully prepared. Then the corresponding metal oxides are obtained by calcining precursors. We systematically study the influence of the morphology and structure of metal oxides Co3O4/Fe2O3 derived from PBAs on their electrochemical performance. The metal oxide with a partially hollow and octahedral structure shows excellent electrochemical performance. In a neutral electrolyte, the specific capacitance is 659.7 F g-1 at a current density of 0.5 A g-1. After 6000 cycles, the capacitance retention rate is 63.7%. An asymmetric supercapacitor (ASC) is constructed using Co3O4/Fe2O3 with an octahedral structure (CFMO-PVP-2) as the positive electrode and YP-50F as the negative electrode. The maximum energy density is 31.4 W h kg-1 at a power density of 1921 W kg-1. The maximum power density is 8421 W kg-1 at an energy density of 23.5 W h kg-1. The excellent electrochemical performance is attributed to the low resistance (Rw and Rct) and high DOH- derived from the oxide particles on the surface and within the inner parts of the octahedron, which are available for electron transport. Meanwhile, the open void between adjacent nanoparticles allows the electrolyte ions to diffuse more efficiently and ensures a much more effective area for participating in a reaction. The strategy will give new insights into designing high-performance SCs based on PBAs.

Prussian blue analogue-derived hollow metal oxide heterostructure for high-performance supercapacitors

Supercapacitors (SCs) have been the subject of considerable interest because of their distinct advantages. The performance of SCs is directly affected by the electrode materials. Metal oxides derived from Prussian blue analogues (PBAs) are often used as electrode materials for SCs. Herein, we developed a multi-step strategy to fabricate ternary hollow metal oxide (CuO/NiO/Co3O4) heterostructures. The core-shell structured PBA (NiHCC@CuHCC) with Ni-based PBA (NiHCC) as the core and Cu-based PBA (CuHCC) as the shell was prepared by a crystal seed method. The ternary metal oxide (CuO/NiO/Co3O4) with a hollow structure was obtained by calcinating NiHCC@CuHCC. The prepared CuO/NiO/Co3O4 demonstrates an excellent specific capacitance of 262.5 F g-1 at 1 A g-1, which is 27.4% and 16.2% higher than those of CuO/Co3O4 and NiO/Co3O4, respectively. In addition, the material showed outstanding cycling stability with a capacitance retention of 107.9% after 3000 cycles. The two-electrode system constructed with CuO/NiO/Co3O4 and nitrogen-doped graphene hydrogel (NDGH) demonstrates a stable and high energy density of 27.1 W h kg-1 at a power density of 1037.5 W kg-1. The capacitance retention rate was 100.7% after 4000 cycles. The reason for the excellent electrochemical properties could be the synergistic effect of the introduced heterojunction of CuO/NiO, the hollow structure, and various metal oxides. This strategy can greatly inspire the construction of SC electrodes.

Emerging 2D Copper-Based Materials for Energy Storage and Conversion: A Review and Perspective

2D materials have shown great potential as electrode materials that determine the performance of a range of electrochemical energy technologies. Among these, 2D copper-based materials, such as Cu-O, Cu-S, Cu-Se, Cu-N, and Cu-P, have attracted tremendous research interest, because of the combination of remarkable properties, such as low cost, excellent chemical stability, facile fabrication, and significant electrochemical properties. Herein, the recent advances in the emerging 2D copper-based materials are summarized. A brief summary of the crystal structures and synthetic methods is started, and innovative strategies for improving electrochemical performances of 2D copper-based materials are described in detail through defect engineering, heterostructure construction, and surface functionalization. Furthermore, their state-of-the-art applications in electrochemical energy storage including supercapacitors (SCs), alkali (Li, Na, and K)-ion batteries, multivalent metal (Mg and Al)-ion batteries, and hybrid Mg/Li-ion batteries are described. In addition, the electrocatalysis applications of 2D copper-based materials in metal-air batteries, water-splitting, and CO₂ reduction reaction (CO₂ RR) are also discussed. This review also discusses the charge storage mechanisms of 2D copper-based materials by various advanced characterization techniques. The review with a perspective of the current challenges and research outlook of such 2D copper-based materials for high-performance energy storage and conversion applications is concluded.

Novel rhombus Co3O4-nanocapsule CuO heterohybrids for efficient photocatalytic water splitting and electrochemical energy storage applications

The most appealing and prominent approach for improving energy storage and conversion performance is the development of heterojunction interfaces with efficient and unique metal oxide nanostructures. Rhombus Co₃O₄, nanocapsule CuO, and their heterojunction composites were synthesized using a single-step hydrothermal process. The resulting heterojunction Co₃O₄-CuO nanocomposite outperformed the pristine Co₃O₄ and CuO nanostructures for the electrochemical supercapacitor and water splitting performances. The composite showed 2.4 and 1.3 times higher specific capacitance than the associated pristine CuO and Co₃O₄ nanostructures, while its capacitance was 395 F g^-1 at a current density of 0.5 A g^-1. In addition, long-term GCD results with more than 90% stability and significant capacity retention at higher scan rates revealed the unaffected structures interfaced during the electrochemical reactions. The composite photoelectrode demonstrated more than 20% of photocurrent response with light illumination than the dark condition in water splitting. Co₃O₄-CuO heterostructured composite electrode showed a 0.16 mA/cm² photocurrent density, which is 3.2 and 1.7 times higher than the pristine CuO and Co₃O₄ electrodes, respectively. This performance was attributed to its unique structural composition, high reactive sites, strong ion diffusion, and fast electron accessibility. Electron microscopic and spectroscopic techniques confirmed the properties of the electrodes as well as their morphological properties. Overall, the heterojunction interface with novel rhombus and capsule structured architectures showed good electrochemical performance, suggesting their energy storage and conversion applications.