Improving the Wettability of Thin-Film Rotating Disk Electrodes for Reliable Activity Evaluation of Oxygen Electrocatalysts by Triggering Oxygen Reduction at the Catalyst-Electrolyte-Bubble Triple Phase Boundaries

Thin-filmed rotating disk electrode (RDE) measurement has been intensively used for activity evaluation of electrocatalysts for a wide range of energy conversion reactions. Besides the need of a high quality homogenous catalyst thin film, a good electrode wettability with aqueous electrolytes is highly desired for reliable activity evaluation of electrocatalysts yet experimentally remains a non-trivial task, showing the feasible formation of visible or invisible bubbles at the electrode-electrolyte interface. In this work, we report a robust and facile approach to eliminate these bubbles and thus improve the wettability of thin-filmed catalyst electrodes. This was achieved by triggering oxygen reduction at the catalyst-electrolyte-bubble triple phase boundaries at a constant reductive potential for a while, leading to oxygen depletion in the bubbles and thereby vanishing the bubbles. We also show that, insufficient wettability of catalyst electrodes due to visible or even invisible bubbles can lead to under-estimated activity for oxygen evolution reaction as well as inaccurate oxygen reduction reaction measurement. Once eliminating these bubbles at constant reductive potentials, the RDE tests can be repeatable and more reliable for activity assessment of electrocatalysts.