Oxygen Evolution at IrO₂Shell–Ir−Ni Core Electrodes Prepared by Galvanic Replacement

Abstract

IrO2 shell–Ir−Ni core particulate films (denoted as IrO2 (Ir−Ni)) have been prepared by galvanic replacement of Ni layers electrodeposited on glassy carbon (GC) electrodes. The method involves three steps: immersion of the Ni/GC electrode into a deaerated solution of Ir(IV) at 65 °C for 15 min (galvanic replacement); electrochemical treatment of the resulting Ir−Ni/GC electrode for anodic dissolution of nonreacted surface Ni and surface enrichment in Ir (formation of a precursor core–shell structure denoted as Ir (Ir−Ni)); anodization of the resulting Ir (Ir−Ni)/GC system (iridium dioxide formation). The resulting IrO2 (Ir−Ni)/GC electrodes have been characterized by SEM/EDS, AFM, and XPS, revealing a particulate morphology (submicron particles), an Ir-rich bulk atomic composition (Ir/Ni atomic ratio of ca. 5), and a thin IrO2 shell. Electrochemical characterization in acid solutions in both the H adsorption/desorption and the oxide formation/reduction potential ranges points to complete surface coverage by IrO2. The prepared IrO2 (Ir−Ni)/GC electrodes have been tested as anodes for oxygen evolution (OER) from acid solutions by means of EIS and steady-state current–potential plots; they have been proven to exhibit superior intrinsic catalytic activity for OER compared to that of plain IrO2 anodically grown on bulk Ir.