Electrochemically deposited iridium-oxide: Estimation of intrinsic activity and stability in oxygen evolution in acid solution

摘要

Hydrated iridium oxyhydroxide (IrOx) films were electrochemically deposited from an alkaline oxalic solution at constant anodic potentials and by applying a potential cycling protocol, in both cases with variation of the electrodeposition time. From UV–vis spetroscopy of the solution for the deposition and their characterization it was concluded that a mixture of Ir(III)/Ir(IV) monomers participates in the deposition of IrOxfilm. X-ray photoelectron spectroscopy (XPS) of IrOxfilms indicated that both types of films contained hydrated Ir(IV) hydroxide as the dominant species, but in the film deposited by potential cycling the presence of the additional Ir(III) species was evident. The scanning electon microscopy (SEM) analysis of the surface morphology revealed that films deposited by potential cycling were more uniform than the films deposited at a constant potential. The amount of electrochemically active Ir-species on the surface of deposited IrOxfilms was estimated from the voltammetric charge of the Ir(III)/Ir(IV) transition. Depending on the film electrodeposition parameters, the values between 15 and 1080nmolcm?2were obtained. The electrochemically active surface area (ECSA) of IrOxfilms was calculated from cyclic voltammetry and electrochemical impedance spectroscopy (EIS) measurements and ranged from 3 to 131cm2per 1cm2of geometric surface area for various films. The activity and stability of IrOxfilms toward oxygen evolution reaction (OER) was investigated in 0.5M H2SO4solution under potentiostatic conditions. The intrinsic activity, stated as turnover frequency and specific current density normalized per ECSA, showed that the OER activity of IrOxfilms deposited by potential cycling are up to two and a half times higher than the activity of films deposited at a constant anodic potential. Potentiostatic stability test showed a decrease in OER current over time for both type of the films. Determination of ECSA, the amount of electroactive Ir species, XPS spe