Macrocyclic Copper(II) Electrocatalysts for Water Oxidation: Catalytic Mechanism and Activity of Pyridine-Embedded...

Electrochemical water oxidation (WO) plays a central role in hydrogen production strategies for the energy transition, as it constitutes the main kinetic bottleneck of the overall process. Herein, a computational study was carried out to investigate the mechanism and activity of [Cu(Me₃Pyclen)]²⁺ as an electrocatalyst toward WO, involving the pyridine-embedded macrocylic ligand Me₃Pyclen (Me₃Pyclen = 4,7,10-trimethyl-1,4,7,10-tetraaza-2,6-pyridinophane). Several pyridine-embedded Cu complexes at different electronic states have been computationally determined for the electrooxidation steps, revealing an intricate mechanism for the catalyst activation. Subsequently, the TOF-determining step of the catalytic cycle was estimated to be the O-O coupling via two viable reaction pathways: through single- or double-water coordination modes. In the first pathway, a buffer-mediated water nucleophilic attack coupled with single-electron transfer (SET-WNA) is involved, whereas the second proceeds through an intramolecular oxygen coupling (IOC) mechanism. Additionally, outer-sphere electron transfer steps might play an important role in generating reactive species that promote the O-O coupling. Overall, through a detailed theoretical screening of electrocatalytic reaction steps, we were able to compare the distinct mechanistic features of these electrocatalysts based on their electronic and steric features, possibly opening new possibilities for the rational design of ligands for WO catalyzed by Cu complexes.