Ultrafine Iridium Oxide Nanorods Synthesized by Molten Salt Method toward Electrocatalytic Oxygen and Hydrogen Evolution Reactions

Ultrafine iridium oxide nanorods (IrO2 NRs) were successfully synthesized using a molten salt method at 650 °C. The structural and morphological characterizations of these IrO2 NRs were carried out by powder X-ray diffraction, Raman spectroscopy and electron microscopic techniques. Compared to commercial IrO2 nanoparticles (IrO2 NPs) and previous reports, these IrO2 NRs show enhanced electrocatalytic activity to oxygen and hydrogen evolution reactions by passing either N2 or O2 gas in a 0.5 M KOH electrolyte before electrochemical measurements, including cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. Specifically, the current densities from the as-synthesized IrO2 NRs and commercial IrO2 NPs were measured in 0.5 M KOH electrolyte to be 70 and 58 (OER, deaerated, at 0.6 V versus Ag/AgCl), 71 and 61 (OER, O2, from −0.10 to 1.0 V versus Ag/AgCl at 50 mV/s), and 25 and 14 (HER, deaerated, at −1.4 V versus Ag/AgCl) mA/cm2, respectively. These results are comparable with, and in most cases, higher than reported data in the literature. Therefore, the current study reports not only a novel synthetic process for IrO2 but also a high efficient IrO2 nanostructure, and it is expected that these IrO2 NRs can serve as a benchmark in the development of active OER and HER (photo)electrocatalysts for various applications.