Heat Treatment for Enhancing Ir-Based Catalysts Enclosed in a Carbon Layer for Electrochemical Oxygen Evolution Reaction

Electrochemical water splitting is one of the environmentally friendly methods to produce H2 gas. However, the low cost-competitiveness of water electrolysis compared to other methods, including H2 production from natural gas, is a main hurdle for its commercial use. Therefore, continuous efforts need to be put into water electrolysis systems for improving their energy efficiency, and the development of more active and durable electrocatalysts is one of the critical requirements. This study introduces a simple synthetic procedure of iridium oxide (IrOx) nanoparticles covered by thin carbon shells and the methods to modulate the oxidation states of IrOx and the thickness of carbon shells. The postheat treatment results in the transformation of metallic Ir to Ir4+ in IrOx and oxidative thinning of carbon shells. The synthesized IrOx catalysts are investigated for the electrochemical oxygen evolution reaction (OER). This study covers how the oxidation states of IrOx nanoparticles and carbon shells affect the performance and durability of the OER. Under the optimal conditions of both variables, a current density of 1 A·cm–2 is obtained at a cell voltage of 1.62 V from a single cell of proton exchange membrane water electrolysis (PEMWE).