Rechargeable zinc‐ion batteries (ZIBs) have emerged as a contender in the area of electrochemical energy storage applications due to their low cost and inherent safety. To optimize the battery performances, ZIBs cathode materials with high capacity and cyclability have been intensively studied, with most attention focused on traditional manganese‐ and vanadium‐based materials. Recently, other novel cathode materials including Prussian blue analogues (PBAs), polyanions, metal sulfides, and organic compounds have begun to gain recognition as promising alternatives. These materials exhibit distinct strength such as high operating voltage, additional capacity by new redox chemistry activation, and/or highly reversible cycling process that are particularly desirable for ZIBs applications. To provide the highlight they deserve, this review focuses on introducing the recent progresses of these ZIBs cathodes and demonstrating common strategies adopted for material modification and optimization. Finally, systematic comparisons among the cathode materials are analyzed, along with challenges and perspectives on each category of the cathodes.

Flexible Zn‐air batteries have recently emerged as one of the key energy storage systems of wearable/portable electronic devices, drawing enormous attention due to the high theoretical energy density, flat working voltage, low cost, and excellent safety. However, the majority of the previously reported flexible Zn‐air batteries encounter problems such as sluggish oxygen reaction kinetics, inferior long‐term durability, and poor flexibility induced by the rigid nature of the air cathode, all of which severely hinder their practical applications. Herein, a defect‐enriched nitrogen doped–graphene quantum dots (N‐GQDs) engineered 3D NiCo2S4 nanoarray is developed by a facile chemical sulfuration and subsequent electrophoretic deposition process. The as‐fabricated N‐GQDs/NiCo2S4 nanoarray grown on carbon cloth as a flexible air cathode exhibits superior electrocatalytic activities toward both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), outstanding cycle stability (200 h at 20 mA cm−2), and excellent mechanical flexibility (without observable decay under various bending angles). These impressive enhancements in electrocatalytic performance are mainly attributed to bifunctional active sites within the N‐GQDs/NiCo2S4 catalyst and synergistic coupling effects between N‐GQDs and NiCo2S4. Density functional theory analysis further reveals that stronger OOH* dissociation adsorption at the interface between N‐GQDs and NiCo2S4 lowers the overpotential of both ORR and OER.

advantages of high theoretical energy density and discharge voltage, but struggle with low anode capacity and reversibility. [1][2][3][4][5][6] To this matter, MXenes with excellent conductivity (6000-8000 S cm −1 ) may be an adequate solution given their promising performances in studies as intercalation anode. [7,8] They have a general chemical formula of M n+1 X n T x , with M being early transition metal, X representing carbon and/ or nitrogen, T x are surface terminations such as F, OH, O, Cl, and n can be integer of 1, 2, or 3. [9][10][11] Typically, MXenes are synthesized via selectively etching of A elements from MAX (M n+1 AX n , with A being mostly III A and IVA elements) precursors using hazardous fluoride containing solutions. [12,13] The material family have demonstrated capability in forming flexible three dimensional (3D) foam electrodes with outof-plane porosity through methods such as hard-templating, achieving rapid mass transport and high rate capability desired for battery application. [14] Despite so, low surface area and limited site accessibility of MXenes remain major challenges to be overcome. [15][16][17][18][19] Previous studies have attempted to resolve the limitations by incorporating in-plane porosity on MXene with postsynthesis processing such as sulfur loading-removal and oxidative chemical etching, but these often result in partial oxidation to the undesired TiO 2 . [11,20,21] Alternatively, redox coupling between A-site elements in MAX phases and cations in Lewis acids melts was investigated to explore new MAX phases and surface chemistries to achieve desirable properties for specific applications. [22,23] For example, nonporous MXenes with exclusively Cl-terminations can be obtained using molten salt etching agent, leading to increased lattice symmetry and improved stability. [12,24,25] These developments significantly reduce the environmental impacts of the synthetic process and expanded the range of possible applications for the MXene family, especially in the field of energy storage and conversion. Given such, a fluoride-free process to synthesize in-plane porous MXene with elevated Li + storage capability and cycling stability is highly desired.In this work, a one-step nonhazardous eutectic etching method is reported for the first time to directly synthesize Continuous discoveries in the field of metallic conductive MXenes have shown their feasibility as electrode materials, but their employment remains impeded by low surface area and inhomogeneous edge terminations generated by hazardous HF etching. To solve these problems, for the first time, a eutectic mixture etching strategy is utilized to accomplish one-step synthesis of Cl-terminated MXene (Ti 3 C 2 Cl 2 ) with tunable in-plane porosity from a MAX precursor (Ti 3 AlC 2 ) through manipulating the phase transition of the selected salt melt. Specifically, the temperature and composition of the NaCl/ZnCl 2 salt mixture are controlled to initiate a mechanism that creates and critically preserves the MXene pore structure, l...

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Micro‐supercapacitors (MSCs) as a new class of energy storage devices have attracted great attention due to their unique merits. However, the narrow operating voltage, slow frequency response, and relatively low energy density of MSCs are still insufficient. Therefore, an effective strategy to improve their electrochemical performance by innovating upon the design from various aspects remains a huge challenge. Here, surface and structural engineering by downsizing to quantum dot scale, doping heteroatoms, creating more structural defects, and introducing rich functional groups to two dimensional (2D) materials is employed to tailor their physicochemical properties. The resulting nitrogen‐doped graphene quantum dots (N‐GQDs) and molybdenum disulfide quantum dots (MoS2‐QDs) show outstanding electrochemical performance as negative and positive electrode materials, respectively. Importantly, the obtained N‐GQDs//MoS2‐QDs asymmetric MSCs device exhibits a large operating voltage up to 1.5 V (far exceeding that of most reported MSCs), an ultrafast frequency response (with a short time constant of 0.087 ms), a high energy density of 0.55 mWh cm−3, and long‐term cycling stability. This work not only provides a novel concept for the design of MSCs with enhanced performance but also may have broad application in other energy storage and conversion devices based on QDs materials.