A design of an economical electrochemical catalyst with controlled pore structure for oxygen evolution reaction

Abstract

Efforts to decarbonize energy sources are intensifying to reduce carbon emissions and prevent environmental pollution. Consequently, hydrogen, which can address these challenges, is gaining attention as a clean energy source. Green hydrogen, produced through electrolysis, has a minimal carbon footprint and is considered the ideal form of hydrogen for the future. Proton exchange membrane water electrolysis (PEMWE), one of the methods for hydrogen production, is being actively studied due to its advantages of operating at high current densities and enabling device miniaturization. In PEMWE, the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) occur simultaneously. However, since the OER occurs under harsh conditions such as high voltage and low pH, it is necessary to use a noble metal catalyst with high activity and durability. To reduce the price of hydrogen production and enhance its competitiveness, research is needed to lower the cost of the electrode layers in the electrolysis system. Enhancing the catalyst's performance relative to its usage is crucial to decreasing the amount of noble metals in the OER catalyst. Support materials can disperse catalyst nanoparticles and prevent them from agglomerating. Furthermore, catalyst performance can be improved by reducing the proportion of noble metals and facilitating electron transfer between the catalyst material and the support. Currently, extensive research is being conducted to identify superior support materials based on in-situ mechanism analysis. Therefore, research was conducted to reduce the amount of precious metals used in OER catalysts for PEMWE and to create a more active catalyst. A highly active supported catalyst containing Ir dispersed in multiporous tantalum oxide (M-Ta2O5) containing both macropores and mesopores was synthesized. The supported iridium nanostructures on the M-Ta2O5 enhance the utilization of Ir and exhibit larger electrochemical surface areas. With 30 wt.% Ir loading, Ir/M-Ta2O5 expresses an overpotential of 290.4 ± 3.5 mV at 10 mA cm-2 and a mass activity of 730.5 ± 44.6 A gIr-1 at 1.55 VRHE. Consequently, Ir/M-Ta2O5 can be effectively utilized to fabricate membrane electrode assemblies with a minimal Ir loading of 0.2 mg cm-2 and Nafion® 115 membrane. This remarkable catalytic performance is evidenced by the achievement of 2.5 A cm-2 at 1.89 V at the single-cell level, underscoring the potential of Ir/M-Ta2O5 as a highly efficient and cost-effective OER catalyst for PEMWE.