Noble metal-free N-doped carbon-based electrocatalysts for air electrode of rechargeable zinc-air battery

Low-cost, high-energy density, and safe zinc-air batteries (ZABs) have been considered to be one of the most potential green energy storage devices. However, the performance of ZABs is affected by the properties of various components, including the passivation and corrosion of the Zn anode, the alkali nature of electrolyte, and especially the slow O-2 oxidation-reduction reaction on the air cathode. Among various components, the cathode electrocatalyst is highly important to the performance of ZABs. N-doped carbon-based materials as electrocatalysts have the advantages of low price, good stability, controllable structure, and high conductivity, which can effectively improve the overall performance of ZABs. Up to now, a number of papers have been published in this field, but there is no systematic review of the latest progress of N-doped carbon-based materials for ZABs. This review paper provides a timely and comprehensive summary of this rapidly developing and important field. In this paper, the important components and working principle of ZABs are firstly introduced and the progress of the anode and electrolyte of ZABs is briefly introduced. Then, the current advanced optimization strategies of N-doped carbon-based catalysts for ZABs are provided, including a variety of common methods for the preparation of N-doped carbon catalysts. In addition to metal-free N-doped carbon-based catalysts, the research progress of N-doped carbon-based catalysts coupled with nonnoble metals is also discussed. In this paper, the properties, preparation methods, and detailed mechanism of various catalysts are summarized systematically and their advantages and disadvantages are discussed. This paper not only introduces the latest research progress, but also provides the basic idea to guide the design of N-doped carbon-based electrocatalysts with high performance, which is helpful for their large-scale applications in ZABs.