This review addresses the importance of the air–electrode structure and the microstructures of the catalyst for rechargeable zinc–air batteries.

This review focuses on graphene-based electrode materials and discusses their problems in full cells and efforts to solve them.

A lightweight, flexible, and highly efficient energy management strategy is highly desirable for flexible electronic devices to meet a rapidly growing demand. Herein, Ni–Co–S nanosheet array is successfully deposited on graphene foam (Ni–Co–S/GF) by a one‐step electrochemical method. The Ni–Co–S/GF composed of Ni–Co–S nanosheet array which is vertically aligned to GF and provides a large interfacial area for redox reactions with optimum interstitials facilitates the ions diffusion. The Ni–Co–S/GF electrodes have high specific capacitance values of 2918 and 2364 F g−1 at current densities of 1 and 20 A g−1, respectively. Using such hierarchical Ni–Co–S/GF as the cathode, a flexible asymmetric supercapacitor (ASC) is further fabricated with polypyrrple(PPy)/GF as the anode. The flexible asymmetric supercapacitors have maximum operation potential window of 1.65 V, and energy densities of 79.3 and 37.7 Wh kg−1 when the power densities are 825.0 and 16100 W kg−1, respectively. It's worth nothing that the ASC cells have robust flexibility with performance well maintained when the devices were bent to different angles from 180° to 15° at a duration of 5 min. The efficient electrochemical deposition method of Ni–Co–S with a preferred orientation of nanosheet arrays is applicable for the flexible energy storage devices.

Energy storage and conversion have attained significant interest owing to its important applications that reduce COi emission through employing green energy. Sorne promising technologies are included metal air batteries, metal sulfur batteries, met al ion batteries, electrochemical ca pacitors, etc. Here, metal elements are involved with lithium, sodium, and magnesium For these devices, electrode materials are of importance to obtain high performance. Two dimensional (2D) materials are a large kind of layered structured materials with promising future as energy storage materials, which include graphene, black phosporus, MXenes , covalent organic frameworks ( COFs ), 2D oxides, 2D chalcogenides, and ot hers. Great progress has been achieved to go ahead for 2D materials in energy storage and conversion. More researchers will j oin in this res earch field. Under the background, it has motivated us to c ontribute with a roadmap on 'two dimensional materials for energy storage and conversion.

Here, a free-standing electrode composed of cobalt phosphides (Co2P) supported by cobalt nitride moieties (CoNx) and an N,P-codoped porous carbon nanofiber (CNF) in one-step electrospinning of environmentally friendly benign phosphorous precursors is reported. Physiochemical characterization revealed the symbiotic relationship between a Co2P crystal and surrounding nanometer-sized CoNx moieties embedded in an N,P-codoped porous carbon matrix. Co2P@CNF shows high oxygen reduction reaction and oxygen evolution reaction performance owing to the synergistic effect of Co2P nanocrystals and the neighboring CoNx moieties, which have the optimum binding strength of reactants and facilitate the mass transfer. The free-standing Co2P@CNF air-cathode-based Zn–air batteries deliver a power density of 121 mW cm–2 at a voltage of 0.76 V. The overall overpotential of Co2P@CNF-based Zn–air batteries can be significantly reduced, with low discharge–charge voltage gap (0.81 V at 10 mA cm–2) and high cycling stability, which outperform the benchmark Pt/C-based Zn–air batteries. The one-step electrospinning method can serve as a universal platform to develop other high-performance transition-metal phosphide catalysts benefitting from the synergy effect of transition nitride satellite shells. The free-standing and flexible properties of Co2P@CNF make it a potential candidate for wearable electronic devices.

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A free-standing vertically aligned CNT array supported on graphene foam is used as an air-breathing electrode for rechargeable Zn–air batteries.