Active and durable R₂MnRuO₇ pyrochlores with low Ru content for acidic oxygen evolution

Area of Science:

• Materials Science
• Electrochemistry
• Green Chemistry

Background:

• The oxygen evolution reaction (OER) is a key bottleneck in green hydrogen production using water electrolyzers.
• Current state-of-the-art OER electrocatalysts rely heavily on iridium (Ir), a precious and scarce metal.
• Ruthenium (Ru)-based catalysts present a viable alternative if their performance can be significantly enhanced.

Purpose of the Study:

• To investigate the potential of low-ruthenium pyrochlores (R₂MnRuO₇) as highly active and durable electrocatalysts for the OER in acidic media.
• To understand the structure-performance relationship governing the OER activity of these novel materials.
• To evaluate the performance of these Ru-based catalysts in a functional water electrolyzer.

Main Methods:

• Synthesis and characterization of low-Ru-content pyrochlores (R₂MnRuO₇, where R = Y, Tb, Dy).
• Electrochemical evaluation of OER activity and durability in acidic media using techniques like linear sweep voltammetry and chronoamperometry.
• Computational modeling (e.g., DFT) and experimental analysis to elucidate the catalytic mechanism.
• Testing of the most promising catalyst (Y₂MnRuO₇) in a water electrolyzer setup.

Main Results:

• Low-Ru-content pyrochlores, particularly Y₂MnRuO₇, demonstrated high activity and excellent durability for the OER.
• Y₂MnRuO₇ exhibited a potential of 1.5 V at 10 mA cm⁻² and maintained stability for 40 hours or 5000 cycles up to 1.7 V.
• Computational and experimental data indicated that the superior performance originates from Ru sites within RuMnOₓ surface layers.
• A water electrolyzer utilizing Y₂MnRuO₇ (0.2 mgRu cm⁻²) achieved 1 A cm⁻² at 1.75 V and remained stable at 200 mA cm⁻² for over 24 hours.

Conclusions:

• Low-ruthenium pyrochlores are highly effective electrocatalysts for the OER, offering a promising alternative to iridium.
• The incorporation of Ru sites within RuMnOₓ surface layers is crucial for the enhanced OER performance.
• Partial substitution of Ru with inexpensive cations in Ru-based catalysts warrants further investigation for improved OER efficiency in green hydrogen production.