Benchmarking Electrocatalyst Stability for Acidic Oxygen Evolution Reaction: The Crucial Role of Dissolved Ion Concentration

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 RuO2 stability. This work explores the influences on
measuring the stability number of RuO2 and presents a comprehensive
analysis and comparison of its stability with other electrocatalysts.
We observe that RuO2 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 RuO2 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 RuO2,
IrO2, and non-noble catalysts demonstrates that RuO2 is at least 2 orders of magnitude less stable but also 10-fold
more active than IrO2 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.