Benchmarking Electrocatalyst Stability for Acidic Oxygen Evolution Reaction: The Crucial Role of Dissolved Ion Concentration
Chao Wei, Zhenbin Wang, Kanan Otani, Degenhart Hochfilzer, Ke Zhang, Rasmus Nielsen, Ib Chorkendorff, Jakob Kibsgaard
Abstract
Developing robust catalysts for the acidic oxygen evolution reaction (OER) is critical for large-scale implementation of proton exchange membrane (PEM) water electrolyzers. A promising strategy is to stabilize Ru-based catalysts by suppressing Ru dissolution, which requires knowledge of RuO 2 stability. This work explores the influences on measuring the stability number of RuO 2 and presents a comprehensive analysis and comparison of its stability with other electrocatalysts. We observe that RuO 2 shows relatively higher stability in electrolytes with a confined working volume because of the Nernst shift caused by the concentration buildup of dissolved Ru. The stability number of RuO 2 has a negligible dependence on the measurement duration, applied current density, Nafion content, and substrate materials. Furthermore, we analyze the effects of these factors on other typical OER catalysts and identify that the concentration of dissolved ions is key to understanding the stability number measured by different electrochemical cells and the claimed excellent stability of non-noble catalysts reported in the literature. In addition, the comparison of the stability number and intrinsic activity of RuO 2, IrO 2, and non-noble catalysts demonstrates that RuO 2 is at least 2 orders of magnitude less stable but also 10-fold more active than IrO 2 and that noble catalysts significantly outperform non-noble catalysts in terms of both stability and activity, posing a grand challenge in developing robust OER catalysts. This work establishes a baseline for enhancing the stability of Ru-based OER catalysts in acidic liquid cells and provides a valuable reference for PEM water electrolyzers.