Deactivated Pt Electrocatalysts for the Oxygen Reduction Reaction: The Regeneration Mechanism and a Regenerative Protocol

Ambient contaminants, e.g., sulfur dioxide (SO2), lead to severe Pt deactivation and performance loss of practical proton exchange membrane (PEM) fuel cells, which need to be removed immediately. We herein find that only partially adsorbed SO2 can be oxidized and removed at up to 1.5 V, even for a longer period. By contrast, interestingly, dynamic potential scanning for several cycles (usually > 8) can gradually regenerate poisoned Pt/C. In situ infrared spectroscopy demonstrates that parallel-bonded SO2 is forbidden to be electro-oxidized at a high potential but can be converted to easily oxidized atop-bonded and bridge-bonded SO2 at a low potential. Due to the potential-dependent transformation, SO2 is gradually oxidized and removed under dynamic potential scanning instead of potentiostatic polarization. Based on this regeneration mechanism, we propose a square wave-based protocol to completely regenerate SO2-poisoned Pt surfaces within unprecedented three cycles.