In Situ Imaging of Electrochemically Induced Oxygen Spillover on Pt/YSZ Catalysts

摘要

Following the pioneering work of Vayenas and co-workers, the feasibility of electrochemical promotion of heterogeneously catalyzed reactions has been demonstrated in the past two decades with porous metal catalysts interfaced to solid electrolytes. The catalytic activity of electrically polarized porous metal electrodes on solid electrolytes has been investigated in over 100 reaction systems, and up to 200-fold increases in rate have been reported. Mechanistically, the promotion effect has been attributed to a charged mobile species that is (partially) discharged at the triple-phase boundary (tpb) (solid electrolyte/metal/gas) and then diffuses over the metal surface, thereby modifying its catalytic activity. The crucial role of the electrochemically generated spillover species and its chemical identity have been proven in recent years by surface analytical techniques for only two systems: the oxygen-ion-conducting Pt/YSZ system (YSZ=yttria-stabilized zirconia, ZrO2 + Y2O3) and the alkali-ion-conducting Pt/-Al2O3 system. We report herein the imaging of the spillover process itself. We observe the diffusional spreading of oxygen upon electrochemical pumping on a dense platinum film interfaced with YSZ. The experiments provide a better basis for a detailed mechanistic understanding of the electrochemical promotion of surface reactions.