Structure–Activity–Stability Relationship of Ru-Ir-Ti Electrocatalysts for the Oxygen Evolution Reaction
Authors: Lahn Leopold , Saveleva Viktoriia A. , Mingers Andrea M. , Vorlaufer Nora , Khanchandani Heena , Felfer Peter , Kasian Olga 
Published: August 2024

Environmentally friendly strategies for energy conversion and storage are urgently needed to account for natural intensity variations of power generation by renewables and to ensure a stable electrical grid. Green hydrogen, produced by water electrolysis, can be considered as one of the most promising energy carriers since it can balance the energy demand in multiple energy sectors. Proton exchange membrane water electrolyzers (PEMWE) are state of the art devices for on-site hydrogen production. Still, their upscaling is challenged by the corrosive acidic environment and sluggish anodic oxygen evolution reaction (OER), which demand using noble metal based catalysts [1, 2]. Currently, Ir-based oxides are employed as OER catalysts in commercial PEMWE as they provide the best balance between activity and stability. Yet, the scarcity and high market price of Ir lead to poor cost-benefit factors. In the last years, Ir-Ru mixed oxides have attracted significant attention of the community due to their improved electrocatalytic activity [2, 3]. However, Ru degradation during the OER becomes challenging in conditions of long-term operation of the electrolyzer. Therefore, balancing stability and activity towards the OER at reduced Ir loading remains a significant challenge in PEMWE.

Here, we examine the effect of low additions of Ti (1 to 6 at. %) on the catalytic activity and stability of Ru-Ir alloys towards the OER [4]. The catalysts are synthesized as ternary Ru-Ir-Ti thin film material libraries with Ir contents below 50 at. %. After the high-throughput screening of these libraries for desired electrocatalytic properties by online inductively coupled plasma mass spectrometry (ICP-MS), the most promising alloy compositions are selected and tested in conditions of long-term electrolysis (Figure 1). The observed activity-stability trends are correlated with the electronic structure of the Ru-Ir-Ti catalysts derived from X-ray photoelectron (XPS) and X-ray absorption spectroscopies (XAS). Furthermore, the structural changes in the near-surface regions of these catalysts induced by the OER, are investigated with the aid of atom probe tomography (APT). Our data reveal formation of Ir-Ru hydrous oxide layers in the course of the OER, providing high catalytic activity, while Ti additions promote stabilization of these reactive oxides in the near surface region. Our multidisciplinary approach of combining advanced electrochemical, spectroscopic and atomic-scale characterization methods provides insights on structure-function relationships in electrocatalysis, guiding the rational design of active and stable electrocatalysts.

[1.] Carmo, M., et al., A comprehensive review on PEM water electrolysis. International journal of hydrogen energy, 2013. 38(12): p. 4901-4934.

[2.] Kasian, O., et al., On the Origin of the Improved Ruthenium Stability in RuO2-IrO2 Mixed Oxides. Journal of the Electrochemical Society, 2016. 163(11): p. F3099-F3104.

[3.] Saveleva, V.A., et al., Uncovering the stabilization mechanism in bimetallic ruthenium–iridium anodes for proton exchange membrane electrolyzers. The journal of physical chemistry letters, 2016. 7(16): p. 3240-3245.

[4.] Lahn, L., et al. Low Ti Additions to Stabilize Ru‐Ir Electrocatalysts for the Oxygen Evolution Reaction. ChemElectroChem, 2023, e202300399. DOI: https://doi.org/10.1002/celc.202300399.

Figure 1