Lattice-Relaxation-Enabled Design of Ru-Ir Oxides for Acidic Oxygen Evolution Reaction: Insights from Pair...

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Designing efficient and stable oxygen evolution reaction (OER) catalysts for acidic media is challenging, requiring a balance between Ruthenium (Ru) oxide's high activity and Iridium (Ir) oxide's stability.
• Conventional characterization methods struggle to elucidate the short-range structural and electronic evolution in mixed Ru-Ir oxides, hindering catalyst design.

Purpose of the Study:

• To investigate the structural and electronic transformations in mixed Ru-Ir oxides under varying annealing temperatures (AT) and operando conditions.
• To establish a mechanistic understanding of the activity-stability tradeoff in these catalysts.
• To identify design principles for durable, low-Ir acidic OER catalysts.

Main Methods:

• Combined atomic pair distribution function (PDF) analysis with operando multiedge X-ray absorption spectroscopy (XAS), including extended X-ray absorption fine structure (EXAFS) and high-energy-resolution fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES).
• Surface-sensitive O K-edge spectroscopy was employed to track atomic and electronic transformations.
• Catalyst performance was evaluated in a single-cell proton exchange membrane water electrolyzer.

Main Results:

• An optimized Ru_0.875Ir_0.125O_x-300 (AT) catalyst demonstrated an overpotential of 208 mV at 10 mA cm^-2 and over 100 h of stable operation, outperforming commercial IrO₂ and RuO₂.
• PDF analysis revealed the onset of rutile-like ordering around 300 °C (AT), with cooperative Ir-O bond contraction and Ru-O bond expansion.
• Operando XAS and PDF indicated that mixed-octahedra relaxation, characterized by Ir-O bond shortening and a moderated Ru-O response within a rutile-like framework, governs the activity-stability balance.

Conclusions:

• Lattice relaxation during the transition from low-symmetry to rutile structures is a key mechanistic basis for designing durable, low-Ir acidic OER catalysts.
• The developed catalyst exhibits promising performance and stability under membrane-electrode assembly (MEA) conditions, validating its practical relevance.