Four electron selective O2 reduction by a tetranuclear vanadium(IV/V/hydroquinonate catalyst: application in the operation of Zn-air batteries

The reduction of dioxygen plays a crucial role in both natural and artificial systems exhibiting peroxidase like activity, utilizing O-2 as a cheap and green oxidant in several applications including the development of new effective sources of clean energy. The exploration of new facile and cost-efficient electrocatalysts which promote the interconversion between H2O and O-2 remains a crucial challenge. In this work, the applicability of peroxidase mimicking tetranuclear vanadium(IV/V) hydroquinonate, 1, as a proton-coupled electron transfer (PCET) oxygen reduction electrocatalyst to metal-air batteries is presented. Cyclic and rotating disk voltammetry studies show that the O-2 reduction is associated with the PCET mechanism. Measurements of the O-2 consumption vs. pH reveal that two molecules of 1 reduce one molecule of O-2 supporting a 4e(-) reduction of O-2 to H2O. V-51 NMR spectroscopy used for H2O2 trap experiments supports the 4e(-) reduction of O-2. Exhaustive electrolysis shows that the redox reactions of 1 are fully reversible in the presence of O-2. Compound 1 was used as a catalyst for the O-2 reduction in a Zn-air battery. Aqueous solutions of the complex were transformed into gels by the addition of a small quantity of sulfuric acid. Then, the complex in the form of gel was easily deposited on a carbon cloth electrode and was directly applied for the construction and operation of a Zn-air battery. The presence of the complex resulted in a large increase of the current and the power produced by the cell, particularly in an acidic electrolyte where the complex operates the best. The application of the biomimetic complex 1 in the operation of metal-air batteries opens a new and interesting route for applying such molecules in a wide range of high importance technological applications.

Automated summary

This study explores the application of a vanadium (IV/V) hydroquinone as an oxygen reduction electrocatalyst, demonstrating potential in metal-air batteries. The reduction of oxygen involves a proton-coupled electron transfer mechanism, supported by NMR spectroscopy. The complex performs best in acidic electrolytes, showing significant increases in current and power when applied in the battery.