Stability and activity of organometallic phthalocyanine sheets for oxygen reduction and oxygen evolution reactions: A DFT study

Abstract

Based on density functional theory calculations we investigate the electronic properties, electrochemical stability, and catalytic activity for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) of two-dimensional (2D) metal phthalocyanine conjugated polymers. Three structures were studied: metal phthalocyanine sheets (s-MPc) and those coordinated with MN${}_4$${}_4$ and MO${}_4$${}_4$ ligands (s-MPc-MN${}_4$${}_4$ and s-MPc-MO${}_4$${}_4$) for M = Mn, Fe, and Co. Their electrochemical stability was analyzed using Pourbaix diagrams, while ORR/OER activity was evaluated by the free energy adsorption of the reaction intermediates. Our findings indicate that the electronic properties of these 2D structures strongly depend on the metal center, resulting in metallic, half-metallic, or semiconducting characteristics. In terms of electrochemical stability, we found that s-FePc, s-FePc-FeO${}_4$${}_4$, and s-MnPc-MnO${}_4$${}_4$ are stable across the entire pH range, while s-CoPc and s-CoPc-CoO${}_4$${}_4$ are stable only in neutral and alkaline media. For ORR and OER activity, s-MPc and s-MPc-MO${}_4$${}_4$ (for M = Fe, Co) exhibit overpotentials ranging from 0.3–0.8 V for ORR and 0.4–0.9 V for OER, which are comparable to those of the best commercial catalysts. Therefore, our results suggest that s-FePc and s-FePc-FeO${}_4$${}_4$ demonstrate both stability and ORR activity, making them promising candidates for high-density single-atom catalysts in energy conversion processes.