The Chemical and Electronic Properties of Stability-Enhanced, Mixed Ir-TiOx Oxygen Evolution Reaction Catalysts

van der Merwe M, Garcia-Diez R, Lahn L, Wibowo RE, Frisch J, Gorgoi M, Yang W, Ueda S, Wilks RG, Kasian O, Bär M (2023)

Publication Type: Journal article

Publication year: 2023

Journal

ACS Catalysis American Chemical Society

Pages Range: 15427-15438

DOI: 10.1021/acscatal.3c02948

Abstract

Iridium has emerged as the leading catalyst material for the anodic oxygen evolution reaction (OER) in acidic media. Often, iridium is mixed with more stable materials such as titanium. For these materials, the electronic structure of titanium plays a crucial role since with varying degrees of oxidation titanium transforms to semiconducting or even insulating phases. Yet, the electronic properties of mixed Ir-TiOx catalysts have never been systematically studied. In this study, we correlate the catalytic performance of mixed Ir-TiOx-based OER catalysts with the electronic structure of the surface layers. For this, a thin film material library with a 20-70 at. % Ir (Ir/[Ir + Ti]) compositional gradient was prepared. We used inductively coupled plasma mass spectrometry to test the OER activity and stability of the set of mixed Ir-TiOx catalyst candidate materials. Complementary, Ti L2,3- and O K-edge X-ray absorption spectroscopy and depth-dependent X-ray photoelectron spectroscopy measurements were performed to correlate the catalytic performance with the composition and electronic property profiles of these mixed Ir-TiOx OER anode catalysts. The spectroscopic analysis reveals that titanium is present as an intermixed matrix of semiconductive but stable TiO2, conductive but less stable titanium-suboxides (TiOx), and highly conductive but highly unstable metallic Ti(0). The extent of the titanium oxidation strongly depends on the titanium content, with a lower degree of oxidation observed for lower titanium (and thus higher iridium) contents. For an iridium loading of 70 at. %, the respective mixed Ir-TiOx catalyst showed a similar OER activity to that of the pure metallic iridium (1.74 vs 1.59 VRHE, respectively) but with a 71% lower iridium dissolution rate relative to the pure metallic iridium. This demonstrates the stabilization effect of titanium addition while maintaining high OER activity.

Authors with CRIS profile

Marcus Bär

Involved external institutions

Helmholtz-Zentrum Berlin für Materialien und Energie (HZB) DE Germany (DE) Lawrence Berkeley National Laboratory (LBNL) US United States (USA) (US) National Institute of Materials Science (NIMS) JP Japan (JP)

How to cite

APA:

van der Merwe, M., Garcia-Diez, R., Lahn, L., Wibowo, R.E., Frisch, J., Gorgoi, M.,... Bär, M. (2023). The Chemical and Electronic Properties of Stability-Enhanced, Mixed Ir-TiOx Oxygen Evolution Reaction Catalysts. ACS Catalysis, 15427-15438. https://dx.doi.org/10.1021/acscatal.3c02948

MLA:

van der Merwe, Marianne, et al. "The Chemical and Electronic Properties of Stability-Enhanced, Mixed Ir-TiOx Oxygen Evolution Reaction Catalysts." ACS Catalysis (2023): 15427-15438.

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