Dynamically stabilized PtCuNi/C catalyst enabled by oxygen vacancies in WO_3-x

The replacement of Pt/C catalysts with Pt-based alloy catalysts was considered a promising strategy to reduce platinum-group-metal (PGM) content in proton exchange membrane fuel cell. However, inexpensive transition metal atoms in Pt-based alloy catalysts are subject to metal dissolution issues, leading to stability issues of oxygen reduction reaction (ORR) catalysts. In this work, a PtCuNi/C-WO_3-x catalyst is designed employing non-stoichiometric WO_3-x with abundant oxygen vacancies (O_vac). The WO_3-x can dramatically improve the stability of PtCuNi without sacrificing the activity. Theoretical calculation suggests a decreased vacancy formation energy of W in WO_3-x at the presence of O_vac, as well as increased vacancy formation energies of Pt/Cu/Ni in PtCuNi alloy particles with the existence of surface W dopant. Combined with the experimental discovery of slower dissolution rates of metals in PtCuNi/C-WO_3-x catalyst, a dissolution-induced stability enhancement mechanism is proposed, whereby facilitated dissolution of W atoms from WO_3-x bulk could re-deposit on Pt-alloy surface and inhibit the dissolution of catalytically active metal atoms, revealing a dynamic process that enhances the stability. The PtCuNi/C-WO_3-x also shows great potential to be used as cathode catalyst in membrane electrode assembly for high-temperature proton exchange membrane fuel cells.