Enhancing Acidic Oxygen Evolution Activity by Controlling Oxidation State of Iridium

Han, Xue; Mou, Tianyou; Kang, Sinwoo; Islam, Arephin; Zhao, Xueru; Sasaki, Kotaro; Rodriguez, José A.; Chang, Qiaowan; Liu, Ping; Chen, Jingguang G.

doi:10.1002/ange.202507468

Enhancing Acidic Oxygen Evolution Activity by Controlling Oxidation State of Iridium

Journal Article · Tue Jun 10 00:00:00 EDT 2025 · Angewandte Chemie

DOI:https://doi.org/10.1002/ange.202507468· OSTI ID:2572353

^[1]; Mou, Tianyou ^[1]; Kang, Sinwoo ^[1]; Islam, Arephin ^[1]; Zhao, Xueru ^[1]; Sasaki, Kotaro ^[1]; Rodriguez, José A. ^[1]; Chang, Qiaowan ^[2]; ^[1]; ^[3]

Brookhaven National Laboratory (BNL), Upton, NY (United States)
Washington State Univ., Pullman, WA (United States)
Brookhaven National Laboratory (BNL), Upton, NY (United States); Columbia Univ., New York, NY (United States)

Iridium oxides with high oxidation states have been reported to be effective in enhancing the acidic oxygen evolution reaction (OER) performance. Herein, 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 IrO₂, 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. Further, 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.

View Accepted Manuscript (DOE)

Research Organization:: Brookhaven National Laboratory (BNL), Upton, NY (United States). Center for Functional Nanomaterials (CFN); Brookhaven National Laboratory (BNL), Upton, NY (United States). National Synchrotron Light Source II (NSLS-II); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)

Sponsoring Organization:: USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division (CSGB); USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF)

Grant/Contract Number:: AC02-05CH11231; SC0012653; SC0012704

OSTI ID:: 2572353

Report Number(s):: BNL--228407-2025-JAAM

Journal Information:: Angewandte Chemie, Journal Name: Angewandte Chemie; ISSN 1521-3757; ISSN 0044-8249

Publisher:: German Chemical SocietyCopyright Statement

Country of Publication:: United States

Language:: English

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