Insights into the Acid Stability of Cobalt Electrocatalysts via Time‐Resolved Activity‐Durability Relationships for Tailored Bimetallic Thin Films

ABSTRACT One route to improve material performance and stability for acidic electrochemical technologies involves atomically mixing different metals, a pertinent example being PtCo catalysts for fuel cells. However, there is a need for deeper understanding of how non‐precious components, such as Co, mechanistically behave when combined with other metals during electrocatalysis. Herein, e‐beam physical vapor deposition is utilized to synthesize bimetallic thin films with a low atomic percentage of Co (10 at.%) and a high atomic percentage of Ag, Au, or Pd, each of which is assessed with on‐line inductively coupled plasma mass spectrometry to monitor time‐resolved relationships between electrocatalysis and material dissolution. Notably, each bimetallic thin film significantly extended the stable operating potential window for Co in acidic media (by +0.6 V for Ag Co , +1.0 V for Pd Co , and +1.5 V for Au Co ), while limiting Co loss to around <1 % in the films, whose dissolution corresponded with in situ phase transformations of the host metal. Additionally, when compared to their noble metal counterparts, the bimetallic materials had improved or sustained onset potentials for oxygen electrocatalysis. Altogether, this work demonstrates compositional and electrochemical strategies in which Co stability can be prolonged in acidic media, with the added benefits of sustained electrocatalytic activity and decreased noble metal loading.