Carbon-Supported PtNi Nanocrystals for Alkaline Oxygen Reduction and Evolution Reactions: Electrochemical Activity and Durability upon Accelerated Stress Tests

The PtNi catalyst is among the most active electrocatalysts for the oxygen reduction reaction, but its stability in operation is uncertain. Intuitively, alkaline environments lead to milder degradations than acidic ones, although carbon-supported Pt-group metal nanoparticles are particularly degraded even in dilute alkaline electrolytes. To date, PtNi catalyst durability has not been characterized for alkaline oxygen reduction and evolution reactions (ORR and OER). Herein, carbon-supported shape-controlled PtNi catalysts were compared in terms of activity and durability during alkaline ORR and OER. The PtNi catalysts are shape-controlled Pt-rich alloy, Ni-rich alloy, and Pt core/Ni shell (Pt@Ni) nanoparticles synthesized on Vulcan XC72R carbon. Their morphology and composition were evaluated by identical-location transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction pre- and post-accelerated stress tests. Compared to Pt/C and Ni/C benchmark catalysts, the core-shell and Ni-rich alloy catalysts gave high and stable OER activities. After the accelerated stress test, the catalysts show two features that are believed to play a major role in the durability: a Ni enrichment at the nanoparticles' surface and an improved attachment of the catalyst to the carbon support.