Understanding the Effect of Au in Au–Pd Bimetallic\nNanocrystals on the Electrocatalysis of the Methanol Oxidation Reaction

Abstract

Pd or Pt alloyed with a secondary\nmetal are the typical catalysts\nat the anode for the direct oxidation of methanol. The secondary metal\nis employed to diminish deactivation commonly ascribed to CO poisoning.\nHere we investigate the origin of the improved performance of Au–Pd\ncore–shell and alloy nanocrystals as electrocatalysts for the\nmethanol oxidation reaction (MOR), relative to Pd alone. Monodisperse\nAu–Pd core–shell nanocrystals were synthesized using\nH₂ as a mild reducing agent followed by annealing under\na 5% H₂ atmosphere to produce the Au–Pd alloys.\nThe nanocrystals were characterized using high-resolution electron\nmicroscopy to confirm their structures. The core–shell and\nalloy nanocrystals showed an improvement in specific activity with\nrespect to pure Pd nanocrystals. Importantly, the stability was also\nimproved by the inclusion of Au for both nanocrystals, being 2.7×\nhigher for the alloy than for the core–shell after 30 min,\nwhile the activity is completely lost for the Pd nanocrystals within\n10 min. We show that there is no evidence of CO formation for any\nof the Pd-based catalysts in an alkaline environment. The origin of\nthe improvement in terms of both activity and stability results from\npositive shifts in the PdO formation/reduction potential caused by\nthe presence of Au, which results in more Pd sites available for the\nMOR.