Ultrasmall 2 D Co x Zn 2− x (Benzimidazole) 4 Metal–Organic Framework Nanosheets and their Derived Co Nanodots@Co,N‐Codoped Graphene for Efficient Oxygen Reduction Reaction

作者：Kuangmin Zhao, Suqin Liu, Guanying Ye, Xianli Wei, Yuke Su, Weiwei Zhu, Zhi Zhou, Zhen He · 发表于：ChemSusChem · 年份：2019 · DOI：10.1002/cssc.201902776 · 被引用次数：41 · 研究领域：Electrocatalysts for Energy Conversion、Fuel Cells and Related Materials、Advanced battery technologies research

Abstract The development of nonprecious metal–nitrogen–carbon (M‐N‐C) materials with efficient metal utilization and abundant active sites for the oxygen reduction reaction (ORR) is of great significance for fuel cells and metal–air batteries. Ultrasmall 2 D Co x Zn 2− x (benzimidazole) 4 [Co x Zn 2− x (bim) 4 ] bimetallic metal–organic framework (MOF) nanosheets (≈2 nm thick) are synthesized by a novel bottom‐up strategy and then thermally converted into a core–shell structure of sub‐5 nm Co nanodots (NDs) wrapped with 2 to 5 layers of Co,N‐codoped graphene (Co@FLG). The size of the Co NDs in Co@FLG could be precisely controlled by the Co/Zn ratio in the Co x Zn 2− x (bim) 4 nanosheet. As an ORR electrocatalyst, the optimized Co@FLG exhibits an excellent half‐wave potential of 0.841 V (vs. RHE), a high limiting current density of 6.42 mA cm −2 , and great stability in alkaline electrolyte. Co@FLG also has great ORR performance in neutral electrolyte, as well as in Mg–air batteries. The experimental studies and DFT calculations reveal that the high performance of Co@FLG is mainly attributed to its great O 2 absorptivity, which is endowed by the abundant Co−N x and pyridinic‐N in the FLG shell and the strong electron‐donating ability from the Co ND core to the FLG shell. This elevates the e g orbital energy of Co II and lowers the activation energy for breaking the O=O/O−O bonds. This work sheds light on the design and fabrication of 2 D MOFs and MOF‐derived M‐N‐C materials fo...