Investigation of Ultra-Low Loading of Metallic Oxide Supported Iridium-Based Catalysts in the Proton Exchange Membrane Water Electrolyzers
Authors: Chang Hung-Ming , Serov Alexey , Lyu Xiang , Zenyuk Iryna 
Published: December 2024

Iridium (Ir)-based catalysts have been considered as the most promising oxygen evolution reaction (OER) in the proton exchange membrane water electrolyzer (PEMWE). The scarce supply of Ir potentially restricts the development of the PEMWE technology. Reducing the use of Ir catalysts has become one of the most critical tasks. The activity and durability of PEMWE depend heavily on the catalyst loading.[1] Poor in-plane electric conductivity due to catalyst layer not being continuous at ultra-low loadings (~0.1-0.2 mgIr/cm2) catalyst, results in loss of electronic connection of some portions of catalyst layer. Several studies have proposed various strategies to lower the loading of Ir catalysts,such as altering catalyst morphology,[2] introducing a microporous layer (MPL) between the catalyst layer and PTL to improve electron transport in disconnected catalyst layers,[3] or doping Ir-based catalysts with support materials. [4-5] These approaches enhance both in-plane and through-plane electric conductivity, thereby increasing catalyst utilization.

In this work, heteroatoms were used as supports or dopants to enhance Ir catalyst utilization and enhance the structural and interfacial stability of the catalyst layer. The microstructure of the metallic oxide support allows IrO2 particles to disperse uniformly, thus enhancing the in-plane conductivity of the catalysts layer. Both commercial metallic oxides supported IrO2 catalysts [6] and laboratory-synthesized catalysts were employed in PEMWE. Different catalyst loadings were investigated, including the ultra-low loading (0.11-0.13 mgIr/cm2) catalysts in this study. We conducted several electrochemical characterization experiments to confirm the improvement of the durability and activity for the IrO2/TiOx and IrO2/NbOx, comparing to the unsupported IrOx catalysts with the identical low Ir loading. A 2V-hold for 100-hour of the accelerated stress testing (AST) indicates the more moderate decay in the current density for supported IrO2 catalysts. Cyclic voltammetry (CV) allows us to monitor the changes of surface oxidation state and the morphology of the Ir-based catalysts during the different operating conditions. Finally, the cell performance of various catalysts on the anode in PEMWE were also evaluated and compared. This study is expected to provide a comprehensive understanding of ultra-low Ir loading in PEMWE.

References

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