2-Methylimidazole as a nitrogen source assisted synthesis of a nano-rod-shaped Fe/FeN@N-C catalyst with plentiful FeN active sites and enhanced ORR activity

The development of controllable doping strategies is essential to obtain highly active electrocatalytic materials. Transition metal atoms with corresponding nitrogen coordination have been widely proposed as active centers for electrocatalytic oxygen reduction (ORR) in metal@nitrogen-carbon (M@N-C) electrocatalysts. In this paper, an effective competitive coordination strategy and high-temperature calcination were used to construct a novel complex Fe/FeN@N-C electrocatalyst. The synthesized catalyst, Fe-MIL-101-2-MI, was using 2-methylimidazole as a nitrogen source and a competitive ligand, which affects the nucleation and growth of the crystal. The morphology of the Fe-MIL-101-2-MI is nanorod, which is conducive to electron transport. Moreover, the competitive coordination of 2-methylimidazole promoted the generation of FeN active sites and greatly improved its ORR electrocatalytic performance. A series of Fe/FeN@N-C-X-Ts electrocatalytic samples was synthesized by controlling the doping amount of 2-methylimidazole and different calcining temperatures. Fe/FeN@N-C-2-800 composites exhibit high levels of doped N, even-distribution of Fe nanoparticles, and abundant FeN active sites. It is noteworthy that the half-wave potential of Fe/FeN@N-C-2-800 in the electrocatalytic ORR reaction is 0.813 V (vs. RHE), the initial potential is 0.873 V (vs. RHE), and the limit current density impressively reached 6.04 mA/cm(2). In comparison to commercial Pt/C, the synthesized catalyst showed superior electrocatalytic performance.