Enhancing Acidic Oxygen Evolution Activity by Controlling Oxidation State of Iridium

Han, Xue [Brookhaven National Laboratory (BNL), Upton, NY (United States)] (ORCID:0000000221909227); Mou, Tianyou [Brookhaven National Laboratory (BNL), Upton, NY (United States)]; Kang, Sinwoo [Brookhaven National Laboratory (BNL), Upton, NY (United States)]; Islam, Arephin [Brookhaven National Laboratory (BNL), Upton, NY (United States)]; Zhao, Xueru [Brookhaven National Laboratory (BNL), Upton, NY (United States)]; Sasaki, Kotaro [Brookhaven National Laboratory (BNL), Upton, NY (United States)]; Rodriguez, José A. [Brookhaven National Laboratory (BNL), Upton, NY (United States)]; Chang, Qiaowan [Washington State Univ., Pullman, WA (United States)]; Liu, Ping [Brookhaven National Laboratory (BNL), Upton, NY (United States)] (ORCID:000000018363070X); Chen, Jingguang G. [Brookhaven National Laboratory (BNL), Upton, NY (United States); Columbia Univ., New York, NY (United States)] (ORCID:0000000295922635)

doi:10.1002/anie.202507468

DOE OSTI · 2570580

Enhancing Acidic Oxygen Evolution Activity by Controlling Oxidation State of Iridium

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Abstract

Iridium oxides with high oxidation states have been reported to be effective in enhancing the acidic oxygen evolution reaction (OER) performance. In this work, we develop ultrasmall IrO x nanoparticles (NPs) over titanium nitride (TiN), which undergoes surface oxidation under oxidative conditions to form oxygen‐modified TiN (oxi‐TiN), enabling the formation of highly oxidized Ir δ+ (δ > 4). This IrO x /oxi‐TiN catalyst delivers higher Ir mass activity than commercial IrO 2 , while comparable stability is maintained. The superior OER activity of IrO x /oxi‐TiN is further demonstrated in a proton exchange membrane water electrolyzer (PEMWE), requiring only 1.88 V to reach 3 A cm −2 , achieving the U.S. Department of Energy 2025 target (1.90 V at 3 A cm −2 ). In situ X‐ray absorption spectroscopy (XAS) confirms that the superior OER activity of IrO x /oxi‐TiN originates from highly oxidized Ir δ+ under OER conditions. Density functional theory (DFT) calculations reveal a general correlation between the oxidation state of Ir and OER overpotential. Specifically, the introduction of interfacial oxygen at the Ir/TiN interface increases the oxidation state of deposited Ir δ+ from δ < 4 to δ > 4, decreasing the OER overpotential. This study highlights the critical role of high oxidation states of Ir δ+ in enhancing OER activity, providing guidance for the development of advanced acidic OER catalysts.

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Han, Xue [Brookhaven National Laboratory (BNL), Upton, NY (United States)] (ORCID:0000000221909227), Mou, Tianyou [Brookhaven National Laboratory (BNL), Upton, NY (United States)], Kang, Sinwoo [Brookhaven National Laboratory (BNL), Upton, NY (United States)], Islam, Arephin [Brookhaven National Laboratory (BNL), Upton, NY (United States)], Zhao, Xueru [Brookhaven National Laboratory (BNL), Upton, NY (United States)], Sasaki, Kotaro [Brookhaven National Laboratory (BNL), Upton, NY (United States)], Rodriguez, José A. [Brookhaven National Laboratory (BNL), Upton, NY (United States)], Chang, Qiaowan [Washington State Univ., Pullman, WA (United States)], Liu, Ping [Brookhaven National Laboratory (BNL), Upton, NY (United States)] (ORCID:000000018363070X), Chen, Jingguang G. [Brookhaven National Laboratory (BNL), Upton, NY (United States); Columbia Univ., New York, NY (United States)] (ORCID:0000000295922635). 2025-06-10. Enhancing Acidic Oxygen Evolution Activity by Controlling Oxidation State of Iridium. https://doi.org/10.1002/anie.202507468

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