Low-Temperature and Gram-Scale Synthesis of Two-Dimensional Fe-N-C Carbon Sheets for Robust Electrochemical Oxygen Reduction Reaction

Abstract

The Fe-N-C-based carbon materials, which are generally formed by high-temperature annealing, have been highlighted as a promising alternative to expensive Pt electrocatalysts for oxygen reduction reaction. However, the delicate formation of active sites remains an issue because of decomposition and transformation of the macrocycle during heat treatment. Accordingly, we developed a low-temperature and gram-scale approach to synthesizing iron phthalocyanine (Pc)-embedded two-dimensional carbon sheets by annealing at 450 degrees C. The low temperature annealing process, which is motivated by the synthesis of carbon nanoribbons, is suitable for maintaining the Fe-N-C structure while enhancing coupling with carbon. Our two-dimensional carbon sheets show higher ORR activity than commercial Pt catalyst in alkaline media. Furthermore, the feasibility of real application to alkaline membrane electrolyte fuel cell is verified by superior volumetric current density. In durability point of view, the initial activity is retained up to 3000 potential cycles without appreciable activity loss; this excellent performance is attributed to the structural stabilization and electron donation from the carbon sheet, which occurs via strong electronic coupling. We believe that this low-temperature and large-scale synthesis of a carbon structure will provide new possibilities for the development of electrochemical energy applications.