Heat-Treated Nonprecious Catalyst Using Fe and Nitrogen-Rich 2,3,7,8-Tetra(pyridin-2-yl)pyrazino[2,3-g]quinoxaline Coordinated Complex for Oxygen Reduction Reaction in PEM Fuel Cells

Abstract

Pyrolyzed Fe/N/C catalysts were synthesized using a newly designed and synthesized 2,3,7,8-tetra(pyridin-2-yl)pyrazino[2,3-g]quinoxaline (TPPQ) organic compound as the nitrogen-containing ligand. The structure of TPPQ was deliberately designed to discourage the agglomeration of Fe during heat treatment as well as to provide a concentrated source of nitrogen. Catalysts were prepared by first coordinating TPPQ with Fe, forming Fe–TPPQ complexes, followed by impregnation onto carbon black (KJ600) and pyrolysis at 900 °C. Catalysts with 0.5%, 1%, 2%, 4%, and 8% initial iron content were prepared, and their physical characteristics were determined by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy analysis. Electrocatalytic activity toward the oxygen reduction reaction was evaluated and compared for all catalysts. The best performing catalyst was found to be the catalyst using 2% initial iron content. Evidence of iron metal and carbide particle formation was found for catalysts with initial iron content higher than 2%.