Importance of Surface IrO_x in Stabilizing RuO₂ for Oxygen Evolution

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Polymer electrolyte membrane (PEM) water electrolyzers face challenges due to high precious metal loading and overpotential for the oxygen evolution reaction (OER).
• Developing stable and efficient electrocatalysts is crucial for the widespread adoption of PEM water electrolyzers.

Purpose of the Study:

• To investigate the OER activity and stability of a combined Iridium Oxide (IrO_x)/Ruthenium Dioxide (RuO₂) system in acidic electrolytes.
• To explore the effect of submonolayer IrO_x deposition on RuO₂ thin films for enhanced catalyst stability.

Main Methods:

• Fabrication of RuO₂ thin films with varying submonolayer amounts (1, 2, and 4 Å) of IrO_x deposited on top.
• Operando extended X-ray absorption fine structure (EXAFS) spectroscopy at the Ir L-3 edge to determine structural properties.
• Electrochemical quartz crystal microbalance (EQCM) combined with inductively coupled mass spectrometry (ICP-MS) to monitor corrosion and metal dissolution.

Main Results:

• EXAFS analysis revealed a rutile-type IrO₂ structure with Ru substitution at some Ir sites, indicating IrO_x is at the surface of the RuO₂ film.
• Submonolayer surface IrO_x was found to be critical in minimizing ruthenium dissolution during OER.
• The IrO_x/RuO₂ system demonstrated tunable surface properties for improved electrocatalytic stability.

Conclusions:

• Submonolayer IrO_x deposition on RuO₂ thin films effectively enhances catalyst stability in acidic media.
• This approach minimizes Ru dissolution, a key factor limiting the durability of catalysts in PEM water electrolyzers.
• Tuning surface properties of OER catalysts like RuO₂ is a viable strategy for achieving higher electrocatalytic stability.