Facilitating Oxygen Redox on Manganese Oxide Nanosheets by Tuning Active Species and Oxygen Defects for Zinc‐Air Batteries

Metal Oxide Nanosheet: Synthesis Approaches and Applications in Energy Storage Devices (Batteries, Fuel Cells, and Supercapacitors)

In recent years, the increasing energy requirement and consumption necessitates further improvement in energy storage technologies to obtain high cycling stability, power and energy density, and specific capacitance. Two-dimensional metal oxide nanosheets have gained much interest due to their attractive features, such as composition, tunable structure, and large surface area which make them potential materials for energy storage applications. This review focuses on the establishment of synthesis approaches of metal oxide nanosheets (MO nanosheets) and their advancements over time, as well as their applicability in several electrochemical energy storage systems, such as fuel cells, batteries, and supercapacitors. This review provides a comprehensive comparison of different synthesis approaches of MO nanosheets, as well their suitability in several energy storage applications. Among recent improvements in energy storage systems, micro-supercapacitors, and several hybrid storage systems are rapidly emerging. MO nanosheets can be employed as electrode and catalyst material to improve the performance parameters of energy storage devices. Finally, this review outlines and discusses the prospects, future challenges, and further direction for research and applications of metal oxide nanosheets.

Oxygen Spillover Effect at Cu/Fe2O3 Heterointerfaces to Enhance Oxygen Electrocatalytic Reactions for Rechargeable Zn-Air Batteries

Rational design and synthesis of high-performance electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are critical for practical application of Zn-air batteries (ZABs). In this work, the bifunctional composite Cu-Fe₂O₃/PNC was prepared by a simple and effective wet-hydrothermal coupled dry-annealing synthesis strategy. The Cu-Fe₂O₃/PNC displayed excellent catalytic activity in ORR and OER with a potential difference of 0.63 V. More importantly, the ZAB assembled with Cu-Fe₂O₃/PNC exhibited a high-power density of 138.00 mW cm^-2 and an excellent long-term cyclability. X-ray photoelectron spectroscopy (XPS) demonstrated that the excellent performance is due to the strong electronic interaction between Cu and Fe₂O₃ that arises as a result of the fast electron transfer through the Cu-O-Fe bond and the higher concentration of surface oxygen vacancies. Meanwhile, the spillover factor Bsp/2zF of Cu/PNC and Cu-Fe₂O₃/PNC obtained by the rotating disk experiment was 1.00 × 10^-7 and 1.10 × 10^-7 cm²·s^-1, respectively, indicating that the oxygen spillover effect between Cu and Fe₂O₃ lowers the energy barrier, increases the number of active sites, and alters the rate-determining reaction step. This work demonstrated the significant potential of Cu-Fe₂O₃/PNC in energy conversion and storage applications, providing a new perspective for the rational design of bifunctional electrocatalysts.

Ultra-dispersed copper nanoparticles constructing crystalline-amorphous interface sites for alkaline water splitting

In literature, the creation of an interface between a highly conductive crystalline phase and an amorphous phase with unsaturated sites has been proven to be an effective strategy in the design of electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). However, the procedural complexity and limited formation of interfaces have compromised the envisioned effects. In this work, the dense crystalline Fe₂O₃/amorphous Cu interface was created simultaneously by the combination of solverthermal and annealing processes. The results showed that the ultra-dispersed Cu nanoparticles attributed to the formation of crystalline-amorphous (c-a) interface sites, which facilitated the electron transfer with the tuned electronic structures as well as the favorable adsorption of surface oxygen species. As a result, the developed Fe₂O₃/Cu-PNC catalyst outperformed most of the competing bifunctional catalysts reported for both OER and HER operations.

High-Performance Aqueous Zn Battery Based on MoS2-Loaded MnO2-x@Carbon Aerogel

The MnO₂-based aqueous Zn cell can meet the requirements of safety, flexibility, and low cost for portable/wearable electronics; however, its low intrinsic conductivity, weak kinetics, and poor high-loading capacity restrict its practical performance. In this study, the synergistic architecture of MoS₂-loaded, oxygen-defect-rich MnO_2-x nanocrystals with a carbon coating (M-PM_2-x-H₂ aerogel) was prepared. As corevealed by various characterizations, this synergistic design not only improves the electronic/ionic conductivity but also motivates the conversion kinetics of the surficial electrochemical reaction. As a result, the M-PM_2-x-H₂ cathode delivers a much improved capacity of 567 mA h·g^-1 at 0.1 A·g^-1 and shows a high capacity retention of 176% after 150 cycles at 0.5 A·g^-1. More impressively, the high areal loading (3.97 mg·cm^-1) of the M-PM_2-x-H₂ electrode also displays a high capacity of 367 mA h·g^-1 at 0.1 A·g^-1. In addition, the derived all-solid-state cell exhibits excellent flexibility and safety under the conditions of weight loading, cutting, and bending.