Recent progress on MN₄ macrocycle-derived oxygen reduction reaction electrocatalysts for polymer electrolyte fuel...

Transportation and power generation sectors have been garnering strong support for fuel cell-based technologies in recent times for emission-free energy conversion. However, the performance of these devices largely relies on the costly and scarce Pt-group metal-based electrocatalysts, which hinder their widespread commercialization. For the past few decades, vast research efforts have been focused on cost-effective and efficient non-precious metal electrocatalysts for low-temperature fuel cells. Single-atom catalysts (SACs) have attracted the most attention due to their excellent electrocatalytic performance. Moreover, SACs derived from transition metal MN₄ macrocycles have many advantages in terms of the structural integrity of the active centers that are beneficial for superior electrocatalytic activity and durability. This feature article covers recent reports focused on the development of MN₄ macrocycle-derived oxygen reduction reaction (ORR) electrocatalysts for proton exchange membrane fuel cells (PEMFCs) and anion exchange membrane fuel cells (AEMFCs), and summarizes the viability in energy applications, including their stability issues. This review aims to discuss the various factors that influence the fuel cell performance of cathode catalysts based on transition-metal macrocyclic complexes (metal porphyrins and phthalocyanines).