Solution Processable Cu(II)macrocycle for the Formation of Cu₂O Thin Film on Indium Tin Oxide and Its Application for Water Oxidation

The development of efficient water oxidation catalytic interfaces has become a demanding challenge to fulfill the promise of water splitting for clean energy conversion and storage. The present work reports on the use of a Cu 2+ -macrocycle, formed by the interaction of copper perchlorate hexahydrate with ethylenediamine and 1,4-bis(2-carboxyaldehyde phenoxy)butane, as precursors for the oxygen evolution reaction (OER) on anode. In alkaline solution, using potassium borate electrolyte (pH 12.0) as electrolyte, the catalytic onset potential was less than 0.80 V, reflecting an overpotential of 524 mV for a catalytic current density of 1 mA cm –2 . The OER activity was much higher when compared to Cu 2+ (e.g., Cu(OAc) 2 ), which converts under these conditions into OER inactive Cu(OH) 2 precipitate in solution. The interest of this complex is that it can be used as homogeneous OER catalyst but can be in addition electrochemically deposited on electrode materials, where it maintained its robust electrocatalytic activity for the OER. Surface-supported thin catalytic film was grown on glassy carbon and indium tin oxide (ITO) electrodes upon the application of a potential of 1.1 V for 5 h. X-ray diffraction (XRD) as well as X-ray photoelectron spectroscopy (XPS) indicate the preferential formation of Cu 2 O. Remarkably, under applied anodic potential of 1.1 V vs SCE, the ITO/Cu 2 O anode efficiently catalyze water oxidation by evolving oxygen. The overpotential was determined as 400 mV vs NHE at 1 mA cm –2 . This anode maintained a current density of about 5.1 mA cm –2 for 5 h with a recession of about 11%. In addition, the same ITO/Cu 2 O anode could be used for several OER experiments without loss of activity.