Nitrogen-doped carbon materials derived from metal–organic frameworks (MOFs) have been proposed as promising electrocatalysts for the oxygen reduction reaction (ORR) but still face a great challenge to replace Pt. In this work, a NaCl-assisted exfoliation approach was developed to synthesize three-dimensional (3D) nitrogen doped hierarchical porous carbons (NHPCs) by the pyrolysis of a ZIF-8 polyhedron. At high temperature, NaCl crystals become a molten salt which not only serves as a template wrapping ZIF-8 derived carbon but also as an intercalating agent penetrating through the carbon via capillarity to promote the formation of nanosheets and mesopores and prevent the aggregation of nanosheets. The morphology, graphitization degree and nitrogen type of the resulting carbons are effectively controlled by tuning the NaCl/ZIF-8 mass ratio and pyrolysis temperature. The as-prepared optimal carbons show an intertwined nanosheet structure with rich micro- and mesopores, high surface area, suitable graphitization degree and nitrogen type. Benefiting from these desirable features, the optimal NHPCs exhibit excellent ORR electrocatalytic performances, much better than Pt/C, and also show high capacity and outstanding long-term discharge stability in Zn–air batteries. This work provides a simple and appealing method to prepare hierarchical porous structured carbon materials, and has a great potential to be extended to other MOFs for energy-related applications.

中文翻译：

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从ZIF-8多面体到三维氮掺杂的分级多孔碳：氧还原反应的高效电催化剂†

来自金属有机骨架（MOF）的氮掺杂碳材料已被提出作为氧还原反应（ORR）的有前途的电催化剂，但要取代Pt仍然面临巨大挑战。在这项工作中，开发了一种NaCl辅助剥离方法，可通过ZIF-8多面体的热解来合成三维（3D）氮掺杂分层多孔碳（NHPC）。在高温下，NaCl晶体变成熔融盐，它不仅充当包裹ZIF-8衍生碳的模板，而且还充当通过碳穿透碳的嵌入剂。毛细作用以促进纳米片和中孔的形成并防止纳米片的聚集。通过调节NaCl / ZIF-8的质量比和热解温度，可以有效地控制所得碳的形态，石墨化程度和氮类型。所制备的最佳碳显示出交织的纳米片结构，具有丰富的微孔和中孔，高表面积，合适的石墨化度和氮类型。受益于这些理想的特性，最佳的NHPC具有出色的ORR电催化性能，远优于Pt / C，并且还具有高容量和出色的Zn-空气电池长期放电稳定性。这项工作为制备分层多孔结构碳材料提供了一种简单而吸引人的方法，