The oxygen reduction reaction (ORR) at the cathode is one of the critical bottlenecks in the energy conversion process in polymer electrolyte fuel cells (PEFCs) and metal–air batteries. An iron azaphthalocyanine unimolecular layer (Fe-AZUL) adsorbed onto a carbon substrate exhibited high ORR activity as an alternative of Pt supported on carbon black (Pt/C) electrocatalyst. We herein report the synthesis of various AzPc molecules with different peripheral structures and complex metals, as well as measurements of the ORR activities of catalysts containing the synthesized molecules and carbons. The catalytic activities were characterized by electrochemical analysis, density functional theory (DFT) calculations, and measurements of ionization potential (IP) values. From the results, the IP values on Ketjen Black (KB) were found to be one of the significant indicators for high ORR activities, providing a guideline for the development of high-performance electrocatalysts.

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