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Manganese Oxide/Iron Carbide Encapsulated in Nitrogen and Boron Codoped Carbon Nanowire Networks as Accelerated Alkaline Hydrogen Evolution and Oxygen Reduction Bifunctional Electrocatalysts

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posted on 09.03.2022, 20:13 authored by Zhuo Liu, Fei Guo, Lina Han, Jie Xiao, Xiaoyuan Zeng, Chengxu Zhang, Peng Dong, Mian Li, Yingjie Zhang
Along with the widespread applications of various energy storage and conversion devices, the prices of precious metal platinum (Pt) and transition-metal cobalt/nickel keep continuously growing. In the future, designing high-efficiency nonprecious-metal catalysts based on low-cost iron (Fe) and manganese (Mn) metals for hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) is fairly critical for commercial applications of hydrogen fuel cells. In this study, for the first time, we design novel three-dimensional (3D) hybrid networks consisting of manganese oxide (MnO)-modified, iron carbide (Fe3C)-embedded, and boron (B)/nitrogen (N) codoped hierarchically porous carbon nanofibers (denoted FeMn@BNPCFs). After optimizing the pyrolysis temperatures, the optimal FeMn@BNPCFs-900 catalyst displays the best HER and ORR catalytic activities in an alkaline solution. As expected, the HER onset potential (Eonset) and the potential at a current density of −10 mA cm–2 for FeMn@BNPCFs-900 in 1.0 M KOH are just 36 and 194 mV more negative than the state-of-the-art 20 wt % Pt/C catalyst with more superior stability. In particular, the FeMn@BNPCFs-900 catalyst shows excellent ORR catalytic activity with a more positive Eonset (0.946 V vs RHE), a more positive half-wave potential (E1/2 = 0.868 V vs RHE), better long-term stability, and higher methanol tolerance surpassing the commercial 20 wt % Pt/C (Eonset = 0.943 V vs RHE, E1/2 = 0.854 V vs RHE) and most previously reported precious-metal-free catalysts in 0.1 M KOH. The synergistic effects of 3D hierarchically macro-/mesoporous architectures, advanced charge transport capacity, abundant carbon defects/edges, abundant B (2.3 atom %) and N (4.9 atom %) dopants, uniformly dispersed Fe3C@BNC NPs, and MnO nanocrystallines are responsible for the excellent HER/ORR catalytic activities of the FeMn@BNPCFs-900 catalyst.

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