Low temperature synthesis of Сu0.3IrOx·nH2O nanocrystals by successive ionic layer deposition and their electrocatalytic properties in oxygen evolution reaction during water splitting in acidic medium

Abstract Ultrafine Сu0.3IrOx·nH2O nanocrystals with rutile-like structure were synthesized for the first time on the surface of titanium foil through facile and precise Successive Ionic Layer Deposition (SILD). An aqueous solution of Cu(OAc)2 with the equilibrium pH value and a colloidal solution containing IrOx∙nH2O nanoparticles and Na2Ir(OH)6 with pH = 10.5 obtained by hydrolysis of H2IrCl6 in a NaOH solution were used as reagents. The nanocrystals were investigated by SEM, EDX, TEM, HRTEM, XPS, XRD, and FTIR spectroscopy. As a result of a sequential and repeated treatment of titanium foil according to the SILD method with the reagent solutions, a nanolayer of Cu0.3Ir(OH)x nanocrystals is formed on its surface, which, after heating at a temperature of 200°C, transforms into a porous nanolayer consisting of ultrafine Сu0.3IrOx·nH2O nanocrystals. They have a distorted crystal structure similar to that of rutile with sizes of 2-3 nm and form polycrystals with a thickness of 4-8 nm and lateral sizes of 40-60 nm on the substrate surface. The porous nanolayers of such polycrystals exhibit electrocatalytic properties in the oxygen evolution reaction during acidic water electrolysis. In a series of samples synthesized as a result of 10-30 SILD cycles, the best electrochemical characteristics are demonstrated by a sample acquired after 20 synthetic cycles: the overpotential value is 256 mV and the Tafel slope is 41.4 mV/dec. These results are an experimental validation of a new approach in the search for highly efficient electrocatalysts based on the study of electrochemical properties in a series of samples synthesized as a result of a varying number of SILD cycles and the selection of samples with the best properties.