Efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) processes highly rely on the rational design and synthesis of high‐performance electrocatalysts. Herein, comprehensive characterizations and density functional theory (DFT) calculations are combined to verify the important roles of the crystallinity and oxygen vacancy levels of Co(II) oxide (CoO) on ORR and OER activities. A facile and controllable vacuum‐calcination strategy is utilized to convert Co(OH)2 into oxygen‐defective amorphous‐crystalline CoO (namely ODAC‐CoO) nanosheets. With the carefully controlled crystallinity and oxygen vacancy levels, the optimal ODAC‐CoO sample exhibits dramatically enhanced ORR and OER electrocatalytic activities compared with the pure crystalline CoO counterpart. The assembled liquid and quasi‐solid‐state Zn–air batteries with ODAC‐CoO as cathode material achieve remarkable specific capacity, power density, and excellent cycling stability, outperforming the benchmark Pt/C+IrO2 catalysts. This study theoretically proposes and experimentally demonstrates that the simultaneous introduction of amorphous structures and oxygen vacancies could be an effective avenue towards high‐performance electrocatalytic ORR and OER.

Low cost and green fabrication of high-performance electrocatalysts with earth-abundant resources for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial for the large-scale application of rechargeable Zn–air batteries (ZABs). In this work, our density functional theory calculations on the electrocatalyst suggest that the rational construction of interfacial structure can induce local charge redistribution, improve the electronic conductivity and enhance the catalyst stability. In order to realize such a structure, we spatially immobilize heterogeneous CoS/CoO nanocrystals onto N-doped graphene to synthesize a bifunctional electrocatalyst (CoS/CoO@NGNs). The optimization of the composition, interfacial structure and conductivity of the electrocatalyst is conducted to achieve bifunctional catalytic activity and deliver outstanding efficiency and stability for both ORR and OER. The aqueous ZAB with the as-prepared CoS/CoO@NGNs cathode displays a high maximum power density of 137.8 mW cm−2, a specific capacity of 723.9 mAh g−1 and excellent cycling stability (continuous operating for 100 h) with a high round-trip efficiency. In addition, the assembled quasi-solid-state ZAB also exhibits outstanding mechanical flexibility besides high battery performances, showing great potential for applications in flexible and wearable electronic devices.

Atomically thin materials (ATMs) with thicknesses in the atomic scale (typically <5 nm) offer inherent advantages of large specific surface areas, proper crystal lattice distortion, abundant surface dangling bonds, and strong in-plane chemical bonds, making them ideal 2D platforms to construct high-performance electrode materials for rechargeable metal-ion batteries, metal-sulfur batteries, and metal-air batteries. This work reviews the synthesis and electronic property tuning of state-of-the-art ATMs, including graphene and graphene derivatives (GE/GO/rGO), graphitic carbon nitride (g-C 3 N 4 ), phosphorene, covalent organic frameworks (COFs), layered transition metal dichalcogenides (TMDs), transition metal carbides, carbonitrides, and nitrides (MXenes), transition metal oxides (TMOs), and metal-organic frameworks (MOFs) for constructing nextgeneration high-energy-density and high-power-density rechargeable batteries to meet the needs of the rapid developments in portable electronics, electric vehicles, and smart electricity grids. We also present our viewpoints on future challenges and opportunities of constructing efficient ATMs for next-generation rechargeable batteries.

Further improvement of optoelectronic performance is a target for all-inorganic lead halide perovskite material CsPbBr3; however, it is greatly limited by the quality of the material which is dominated to some extent by defects, especially intrinsic point defects. In this study, the intrinsic point defects in melt-grown CsPbBr3 crystals were studied by thermally stimulated current technology and the simultaneous multiple peak analysis (SIMPA) method. The defect formation mechanism was analyzed systematically by combining the SIMPA fitting results with defect-related parameters, material properties, and external conditions. The main analytical defects, VCs and VBr vacancies, Csi and Pbi interstitials, and PbBr antisites, matched up with theoretical prediction well. Such systematic studies of defect types and concentration give us more insights into the carrier transport mechanism of CsPbBr3 and will help us find ways to improve the crystal quality by controlling the types and concentration of point defects.

The development of nonprecious metal catalysts with highly efficient and durable activities is of great importance for high performances of zinc-air batteries. Herein, the N-doped graphene wrapped Fe 3 C/Fe 2 O 3 heterostructure has been designed as a bifunctional oxygen catalyst for zinc-air batteries. In the synthesis process of the catalyst, graphene oxide (GO) can assemble with graphitic carbon nitride (g-C 3 N 4 ) and FeOOH nanorods by the π−π stacking and hydrogen bonds, respectively. The assembly of GO, g-C 3 N 4 and FeOOH nanorods results in nanostructure of carbon layers coated iron species and leads to outstanding durability in both alkaline and acidic media. The synergistic effect of nitrogen doping and Fe 3 C/Fe 2 O 3 heterostructure allows the catalyst (Fe 3 C/Fe 2 O 3 @NGNs) to display high oxygen reduction and evolution reaction activities. The liquid zinc-air battery assembled with the catalyst presented a remarkable peak power density (139.8 mW cm −2 ), large specific capacity (722 mAh g −1 ) and excellent charging-discharging cycling performance. The quasi-solid-state zinc-air battery with the catalyst exhibited an impressive open-circuit voltage and a peak power density. Therefore, the Fe 3 C/Fe 2 O 3 @NGNs catalyst is expected to have a bright future for practical applications in energy conversion devices.

Exploring inexpensive and earth-abundant transition metal−nitrogen-based carbon (MNC) catalysts to substitute the scarce and costly Pt-based electrocatalysts for the oxygen reduction reaction (ORR) is quite anticipated in metal−air batteries (MABs).Here, we demonstrate a facile vacuum-annealing method to synthesize Cu nanoclusters/FeN 4 amorphous composites embedded in N-doped graphene (Cu/Fe-NG). This approach avoids the long-term pyrolysis procedure and the use of an inert atmosphere in the conventional procedure for fabricating MNC catalysts. Interestingly, we discovered that the amorphous structure of Cu/ FeN 4 composites can provide high-activity bimetallic M−N x sites (M = Cu, Fe), because of which the Cu/FeN 4 composites exhibit boosted electrocatalytic activity with a positive half-wave potential of 0.88 V (vs RHE), long-term durability, and low hydrogen peroxide for the ORR. The origin of this enhancement was assigned to the concomitance of Fe−N 4 and Cu−N x moieties in Cu/Fe-NG, favoring adsorption and activation of the O 2 molecule as suggested by X-ray absorption fine structure (XAFS) analyses and density functional theory (DFT) calculations. Moreover, examinations of Cu/Fe-NG in both liquid and quasi-solid-state Zn−air batteries (ZABs) can exhibit remarkable performances. This work may offer facile fabrication of enhanced performance MNC catalysts as well as a profound insight into the use of amorphous materials in the ORR and ZABs.

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Nitrogen-doped carbon nanotube encapsulating cobalt nanoparticles towards efficient oxygen reduction for zinc-air battery