Facile Fabrication of Ir-Based Gas Diffusion Electrode for Proton Exchange Membrane Water Electrolyzer

Abstract

A production of clean energy is needed to to solve an environment problem and reduce our dependence on fossil fuels. Hydrogen (H2), recognized as one of the most promising clean energy has attracted considerable attention. H2 is generated by a water splitting. Specifically, H2 and oxygen (O2) are electrochemically created from cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) through the water splitting, respectively. The efficiency of water splitting is dependent on anodic OER required to high overpotential (η) due to slow kinetics of OER. An effective strategy to reduce the high η is critical to develop efficient catalysts reducing high η required toward OER. The operation of the Proton Exchange Membrane Water Electrolyzer (PEMWE) has been challenged by low stability and activity of the catalyst for OER in an acidic environment. Herein, a strategy controlling of iridium (Ir) valency through various oxidation methods is proposed that OER catalysts exhibit specific high performance and excellent durability in acid electrolytes. Metallic Ir is made by galvanic displacement caused by the difference of chemical reduction potential. From the metallic Ir, electrochemical (EC) and thermochemical (TC) IrOx are created by applying repeated Cyclic voltammetry (CV) in specific potential range and by heat-treating at 400 °C in air atmosphere, respectively. Metallic Ir, EC and TC IrOx exhibited the overpotential as 261, 270 and 284 mV at 10 mA/cm2, respectively. Especially, metallic Ir and TC IrOx have been maintained the initial performance for 60 h in step-by-step durability tests at 10, 50, 100 mA/cm2. We demonstrated that the performance toward OER is directly affected Ir valency ratio with Ir3+ and Ir4+ related to intrinsic activity and durability, respectively. Thus, a strategy to control the suitable Ir valency to be promising OER catalyst has critical to achieve a balanced activity and stability.