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A novel N,O symmetric double-coordinated configuration of unsaturated Fe single atoms confirmed within a graphene framework (Fe–N,O/G) is demonstrated experimentally and theoretically for a highly active and durable ORR catalyst in Zn-air batteries.

Battery-supercapacitor hybrid devices (BSHDs) are promising for certain applications requiring both high energy and power densities, but restricted by the electrolyte-consuming mechanism and imbalance of charge-storage capacity and electrode kinetics between battery-type and capacitor-type electrodes. Herein, a new prototype of rocking-chair lithium-ion BSHD with high energy and power densities is developed by employing pseudocapacitive T-Nb2O5 with a porous nanoflower structure as the anode and battery-type LiNi0.815Co0.15Al0.035O2 complexed in a three-dimensional interconnected conductive network as the cathode. Benefiting from the rational selection and optimization of the active material and electrode architecture, the anode and cathode exhibit exceptionally matched faradaic capacity and kinetics. Consequently, the BSHD delivers superior performance (165 W h kg−1 at 105 W kg−1 and 9.1 kW kg−1 at 83 W h kg−1) to previously reported rocking-chair BSHDs and could surpass the state-of-the-art electrolyte-consuming BSHDs at the device level. Therefore, this work will open a new avenue towards high-performance BSHDs.

Graphene and other two-dimensional materials (2DMs) have attracted intensive interest for use in energy storage and conversion systems because of their unique structure and remarkable properties. Although significant progress has been made in this field, certain intrinsic limitations obstruct the achievement of desired properties. 2D heterostructures, upon stacking or stitching different 2DMs in well-defined sequences or patterns, could significantly entail drastic changes in their properties, and thereby synergistically combine the merits of individual 2DMs while eliminating their related drawbacks. Herein, we provide a topical review of recent advances in the preparation and characterization of 2D heterostructures for energy-related applications. Firstly, an introduction is given to the definition and importance of 2D heterostructures, followed by their typical categories of vertically stacked heterostructures and horizontal in-plane heterostructures reported so far. Secondly, the state-of-the-art synthesis approaches to fabricate 2D heterostructures, including mechanically aligned transfer, chemical vapor deposition, liquid exfoliation and self-assembly, and layer by layer self-assembly, are introduced in detail. Then, the current status of advanced characterization techniques like scanning probe-, electron-diffraction-, X-ray-, and spectroscopy-based techniques that are critical for the accurate identification of 2D heterostructures and understanding of the performance-enhancing mechanisms of devices is systemically summarized. Furthermore, recent applications of 2D heterostructures in energy storage (e.g., lithium/sodium ion batteries, lithium sulfur batteries, supercapacitors, and micro-supercapacitors) and conversion (e.g., hydrogen/oxygen evolution reactions and photocatalysis) are exemplified to highlight their positive synergistic effect. Finally, future challenges and prospective solutions that may direct the growth of 2D heterostructures and their energy-related applications are proposed.