Design of M-N-C Catalyst By Spray Pyrolysis and Pseudomorphic Transformation As Efficient Electrocatalysts for Oxygen Reduction Reaction

Abstract

Transition metal catalysts with Metal-N-C (M-N-C) sites has been investigated as an alternative of the noble metal catalyst for the oxygen reduction reaction (ORR), which occurs on a cathode of fuel cell. Among the methods of preparing various M-N-C catalysts, carbonized metal organic frameworks (MOF) are the one of the simple ways to synthesize nitrogen-doped carbon. MOF are known highly porous crystalline solids constructed from metal ions or clusters covalently linked by organic ligands. The tunability of their composition, architecture, and properties has has led to advances in drug delivery, catalysis, sensors, optoelectronics, electrochemistry, gas separation and gas adsorption. Although many studies have been reported that M-N-C catalysts have better performance than Pt catalysts, but most have been reported in alkaline media, and Fe-N-C catalysts have been mainly studied in acidic media. Fe-N-C catalysts have excellent performance; the new M-N-C catalyst should be replaced as it is less stable due to the fenton reaction. In this study, we report the synthesis of a melamine-encapsulated Co-ZnO-C composite as a precursor and template for zeolite-imidazole-frameworks (ZIF-8). This approach allows formation of Co-N-C for constructing unique structures at meso- and macropore scales, while maintaining microporosity. Density functional theory analysis confirms the superior stability of the Co-N-C catalyst over other M-N-C catalysts (M = Fe, Ni, Cr, and Mn). The Co-NC catalyst with a developed pore structure shows remarkable durability (6.7 % performance degradation for 100 h) and full cell performance in H2/O2 under 1 bar of backpressure (723 mW/cm2 of maximum power density).