Electrochemical deposition and characterization of iridium oxide films on Ti2AlC support for oxygen evolution reaction

Two types of iridium oxide films formed at the Ti-2 AlC substrate were investigated: (1) anodically electrodeposited iridium oxide film from the solution based on IrCl(3)xH(2)O; (2) iridium oxide film prepared by cycling thin layer of electrodeposited Ir in the 0.5 M H2SO4 from - 0.25 to 1.20 V. It was shown that during anodic electrodeposition of iridium oxide film (1) coulombic efficiency decreases with increasing anodic potential, being only 3% atE = 0.7 V vs. SCE and 26% atE = 0.62 V vs. SCE. A pair of peaks corresponding to the transition Ir(III)-oxide/Ir(IV)-oxide was present on the CVs recorded in 0.5 M H2SO4. While cycling pure Ir thin layer in the solution of 0.5 M H2SO4 from - 0.25 to 1.20 V (2) up to 100 cycles, typical CV response was characterized with the prepeak and a pair of peaks corresponding to the Ir(III)/Ir(IV)-oxide transition. With the increase of cycles number to 150, additional peak at potential of 1.0 V appeared. This peak was formed on the account of pair of peaks corresponding to the Ir(III)/Ir(IV)-oxide transition. The oxygen evolution reaction (OER) was investigated at both iridium oxide films. It was shown that the Tafel slope for the OER was similar to 40 mV dec(-1)for the first polarization curve, confirming that the rds was a reaction S-OH -> S-O-ads + H++ e(-). As the number of recorded polarization curves increased, the activity of both types of iridium oxide films decreased, due to dissolution of iridium oxide films at the potentials of the OER. It is shown that anodically electrodeposited iridium oxide film is more active for the OER than that obtained by cycling electrodeposited iridium layer. However, both iridium oxide films exhibited insufficient stability.