Unveiling the Degradation of Pt/NbOx/C Catalysts in PEMFCs via In Situ X-ray Absorption Spectroscopy

Among the class of the catalyst that is composed of metal nanoparticles supported on metal oxides (MMO), the Pt/NbO x /C system has shown promising oxygen reduction reaction (ORR) activities as a cathode of proton exchange membrane fuel cells (PEMFCs). Herein, we have studied a series of Pt/NbO x /C catalysts prepared via physical vapor deposition and unraveled the nature of the metal and metal oxide interaction (MMOI) by characterizing this system under reactive conditions. By conducting in situ X-ray absorption spectroscopy (XAS) experiments, we demonstrate that Pt preferably interacts with O but not Nb in the Pt/NbO x /C system. As such, Pt-O interaction benefits the ORR activity via an electronic effect rather than a strain effect. We have also provided clear evidence for the formation of metallic Nb phase at the early stage of PEMFC operation, which led to severe particle growth of Pt after long-term PEMFC operation.