Computational Investigation on the Mechanism of Electrocatalytic Water Oxidation by Copper(II) Porphyrin

ABSTRACT This study uses density functional theory (DFT) based calculations to understand the water oxidation process using a copper–porphyrin complex. Three possible reaction pathways (mechanisms) are explored. Through a series of steps involving the proton‐coupled electron transfers (PCETs), the complex changes its oxidation state from II to IV, forming high‐valent copper–oxo species ([LCu IV = O], L = porphyrin). The metal oxo species then allows another water molecule to attack, eventually forming an oxygen–oxygen (O─O) bond – the important step in oxygen generation. In general, the rest of the electrocatalysis mechanism involves the formation of a peroxo linkage, followed by oxidation to molecular oxygen (O═O). The key differences in Mechanisms I‐III involve the formation of [LCu IV = O]. In Mechanism I, [LCu IV = OH] + is formed at E = 1.26 V vs. SHE, followed by deprotonation. In Mechanism II, the formation of [LCu IV = O] involves PCET from the [LCu III ‐OH] at E = 1.71 V vs. SHE, and the rest of the steps remain the same. In Mechanism III, [LCu III ‐OH] is directly formed from [LCu II = OH 2 ] via PCET at E = 1.56 V. It should be noted that the bottleneck involves the formation of high‐valent copper oxo species.