Ultrafine Iridium-Oxide Solid Solutions for Efficient Acidic Water Oxidation

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• High cost and poor catalytic activity of iridium oxide (IrO2) limit proton exchange membrane water electrolyzer (PEMWE) development.
• Traditional doping methods for IrO2 modification are insufficient for enhancing catalytic performance.

Purpose of the Study:

• To propose dual criteria (cohesive energy and atomic radius discrepancies) for guiding the synthesis of ultrafine IrO2-based solid solutions.
• To develop high-performance, low-iridium oxygen evolution reaction (OER) catalysts for PEMWEs.

Main Methods:

• Utilized cohesive energy (ΔCE) and atomic radius (ΔR) discrepancies to guide the synthesis of M_xIr_1-xO2 solid solutions.
• Fabricated sub-3 nm M_xIr_1-xO2 (x = 33.3%-50%) using Mo and W as heteroatoms.
• Investigated the effects of Mo substitution on IrO2's electronic structure and catalytic activity.

Main Results:

• Mo and W exhibited the lowest ΔCE and ΔR, facilitating alloying and minimizing particle coarsening.
• Mo_1/3Ir_2/3O2 showed modulated Ir-O covalency and abundant Brønsted acid sites, accelerating OER kinetics.
• Mo_1/3Ir_2/3O2 achieved a low OER overpotential (540 mV at 1 A cm⁻²) and excellent stability (700 h).
• PEMWE with Mo_1/3Ir_2/3O2 reached 3 A cm⁻² at 2.26 V and operated stably at 1 A cm⁻² for 625 h.

Conclusions:

• The dual criteria approach successfully guided the synthesis of ultrafine, high-performance IrO2-based catalysts.
• Mo_1/3Ir_2/3O2 offers a promising alternative to conventional IrO2 catalysts for efficient and stable PEMWE operation.
• This work provides a new strategy for designing advanced OER catalysts with reduced iridium content.