Exploring the Inner- and Outer-Sphere Mechanistic Pathways of ORR on M–N–Cs with Pyrrolic MN₄ Motifs

Abstract

Metal-and nitrogen-doped carbon materials (M− N−Cs) have emerged as promising alternatives to costly platinumgroup metals (PGMs) for the oxygen reduction reaction (ORR) in renewable energy applications. Notably, there is increasing experimental and theoretical evidence supporting pyrrolic MN 4 coordination over pyridinic MN 4 in these materials, which aligns closer to the MN 4 geometries found in nature. This study utilizes density functional theory (DFT) to elucidate the ability of each metal to catalyze various ORR mechanisms at the pyrrolic MN 4 sites. Among the M−N−Cs of first−row transition metals, pyrrolic CrN 4 and FeN 4 exhibit exceptional 4e-ORR activity, promoting both inner-and outer-sphere mechanisms and H 2 O 2 dissociation. Pyrrolic CoN 4 is also promising for 2e-ORR catalysis due to its effective outer-sphere electron-transfer capabilities. These findings offer valuable insights for designing sustainable electrocatalysts to exploit the full potential of renewable energy sources, advancing the path toward carbon neutrality.