A Mechanisms Review of Metal Phthalocyanines as Single-Atomic Catalysts in Electrochemical Energy Conversion

Metal phthalocyanines (MPcs) are emerging as model single-atom catalysts (SACs) with atomically defined MN4 cores and tailorable peripheries, enabling precise mechanistic explorations and rational performance tuning. Herein, we review recent progress on carbon-supported MPc catalysts for key electrochemical energy-conversion reactions, including the oxygen reduction/evolution (ORR/OER), hydrogen evolution (HER), CO2 reduction (CO2RR) and nitrogen/nitrate reduction (N2RR/NO x RR) reactions. We emphasize mechanistic insights obtained from density-functional theory (DFT) and how π-π stacking, defect engineering, and curvature in graphene or carbon nanotubes modulate the electronic structure of MPcs, optimize intermediate adsorption, and suppress competing pathways. Meanwhile, we focus on specific computational methods like grand-canonical DFT (GC-DFT) and ab initio molecular dynamics (AIMD), which provide potential- and solvent-explicit descriptions of reaction energetics, bridging gaps between conventional constant-charge calculations and experimental observations. Besides, the machine-learning (ML) applications in MPc screening and identification based on metal centers, axial ligands, and dual-site motifs are discussed, followed by a future outlook of remaining challenges and further development of next-generation MPc-based catalysts for sustainable energy technologies.