Surface Reconstruction of Iridium Nanoparticles for Enhanced Oxygen Evolution Reaction in Alkaline Medium

Abstract

An electrochemical water splitting is a promising technology that can generate green hydrogen using renewable energy sources. However, the sluggish oxygen evolution reaction (OER) in an anodic side hinders their large scale applications. Many efforts have been focused on developing efficient electrocatalysts; iridium-based catalysts have gained much attentions due to remarkable intrinsic activities and high stability. Technically, however, the properties are derived from amorphous iridium oxide (IrOx) rather than metallic Ir. During an electrochemical activation process, the Ir metal is easily converted into oxidized species with multiple oxidation states of iridium, which are highly active toward OER. Similarly, many catalysts undergo changes during OER process (e.g., oxidation of precatalysts), resulting in enhancement of activities for OER beyond corresponding original catalysts. Accordingly, the reconstruction process involving surface oxidation and leaching of metal cations should be investigated to develop efficient OER electrocatalysts.Herein, we prepared chalcogen atom modified Ir/IrOx core/shell nanoparticles for enhanced alkaline OER performances (electrolyte: 1M KOH). The S-modified Ir/IrOx exhibited remarkable OER performances with current density of 10 mA cm−2 at overpotentials as low as 180 mV. Incorporation of chalcogen atoms induce surface reconstruction of the Ir/IrOx nanoparticles during OER measurements. It was observed that electrocatalytic activities of Ir/IrOx were varied depending on the type and concentration of chalcogen atoms. There were no observable morphological and structural changes in Ir/IrOx electrocatalyst, whereas the atomic ratio of chalcogen atoms noticeably decreased after OER tests. The result suggests that incorporated chalcogen atoms play a role in modifying the surface of Ir nanoparticles, rather than participating OER as active sites. In addition, XPS measurements were conducted in order to detect changes in chemical states of the catalysts during electrochemical process. We thus believe that the chalcogen atom induced surface reconstruction can be the strategy to efficiently improve the various electrochemical reactions.