Enhancing Acidic Oxygen Evolution Activity by Controlling Oxidation State of Iridium

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Iridium oxides (IrOx) with high oxidation states are crucial for enhancing acidic oxygen evolution reaction (OER) performance.
• Developing efficient and stable catalysts is essential for advanced water electrolysis technologies.

Purpose of the Study:

• To develop ultrasmall IrOx nanoparticles supported on titanium nitride (TiN) that form oxygen-modified TiN (oxi-TiN) under oxidative conditions.
• To investigate the formation of highly oxidized Irδ+ (δ > 4) and its impact on OER activity.
• To demonstrate the catalyst's performance in a proton exchange membrane water electrolyzer and elucidate the mechanism behind its enhanced activity.

Main Methods:

• Synthesis of ultrasmall IrOx nanoparticles over TiN.
• Surface oxidation of TiN to form oxygen-modified TiN (oxi-TiN).
• In situ X-ray absorption spectroscopy (XAS) to confirm the oxidation state of Ir.
• Density functional theory (DFT) calculations to understand the electronic structure and reaction mechanism.
• Performance testing in a proton exchange membrane water electrolyzer.

Main Results:

• The IrOx/oxi-TiN catalyst enables the formation of highly oxidized Irδ+ (δ > 4).
• IrOx/oxi-TiN exhibits higher Ir mass activity compared to commercial IrO2 with comparable stability.
• The catalyst achieved a low potential of 1.88 V at 3 A cm-2 in a proton exchange membrane water electrolyzer, meeting the U.S. Department of Energy 2025 target.
• In situ XAS and DFT calculations confirmed that high oxidation states of Irδ+ and interfacial oxygen are critical for reducing the OER overpotential.

Conclusions:

• Ultrasmall IrOx nanoparticles on oxi-TiN are highly effective for acidic OER.
• The formation of highly oxidized Irδ+ (δ > 4) at the IrOx/oxi-TiN interface is key to superior catalytic activity.
• This work provides a pathway for designing advanced electrocatalysts for efficient water splitting by controlling the metal oxidation state.