Electrochemical Water Oxidation Mechanisms Involving Macrocyclic Copper(II) Complexes: Ligand Ring Size Effects on...

Area of Science:

• Catalysis
• Computational Chemistry
• Materials Science

Background:

• Electrocatalytic water oxidation is crucial for H2 production.
• Modulating transition metal complexes is key to enhancing catalytic performance.
• Previous studies explored [Cu(14-TMC)]2+ (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) for water oxidation.

Purpose of the Study:

• To theoretically investigate the mechanistic impacts of reducing the ring size of macrocyclic copper catalysts.
• To analyze the water oxidation catalytic cycle mediated by [Cu(12-TMC)]2+.
• To compare the mechanistic features of [Cu(14-TMC)]2+ and [Cu(12-TMC)]2+.

Main Methods:

• Density Functional Theory (DFT) calculations.
• Evaluation of electrochemical oxidation, O-O bond formation, and O2 evolution steps.
• Comparative analysis of catalytic cycles and intermediates.

Main Results:

• Ligand ring size influences catalyst electronics, steric hindrance, and coordination numbers.
• O-O bond formation is the rate-determining step for both catalysts, with distinct intermediate structures.
• Comparable Gibbs free energy barriers were computed: 18.96 kcal/mol for [Cu(12-TMC)]2+ and 19.26 kcal/mol for [Cu(14-TMC)]2+.
• [Cu(12-TMC)]2+ displays more intricate mechanisms due to ligand reorganization susceptibility.

Conclusions:

• Reducing macrocyclic ligand ring size in copper catalysts affects water oxidation mechanisms.
• Despite similar energy barriers, [Cu(12-TMC)]2+ offers a more complex catalytic pathway.
• Theoretical insights guide the design of efficient electrocatalysts for hydrogen production.