Mechanism of Cathodic Performance Enhancement by a Few-Nanometer-Thick Oxide Overcoat on Porous Pt Cathodes of Solid Oxide Fuel Cells

In a recent report, we demonstrated that few-nanometer-thick yttria-stabilized zirconia (YSZ) coating on a porous Pt cathode of a solid oxide fuel cell is an excellent facilitator of oxygen reduction reaction (ORR) kinetics and an effective suppressor of Pt agglomeration. In this article, we reveal the actual role of the YSZ overcoat in the ORR process through a series of electrochemical analyses. Without the overcoat, the nanoporous Pt is significantly agglomerated during a high-temperature operation and the ORR becomes limited by the availability of triple phase boundaries (TPBs). An ultrathin YSZ overcoat prevents the ORR process from being limited by TPB area by preserving the morphology of its underlying Pt layer. More importantly, the overcoat acts as an excellent facilitator of the atomic-oxygen-species-mediated chemical process(es) that used to be rate-limiting in the ORR of a noncoated Pt/YSZ system.