Nanoscale compositional changes and modification of the surface reactivity of Pt3Co/C nanoparticles during proton-exchange membrane fuel cell operation
✍ Scribed by L. Dubau; F. Maillard; M. Chatenet; J. André; E. Rossinot
- Publisher
- Elsevier Science
- Year
- 2010
- Tongue
- English
- Weight
- 819 KB
- Volume
- 56
- Category
- Article
- ISSN
- 0013-4686
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✦ Synopsis
This study bridges the structure/composition of Pt-Co/C nanoparticles with their surface reactivity and their electrocatalytic activity. We show that Pt 3 Co/C nanoparticles are not stable during PEMFC operation (H 2 /air; j = 0.6 A cm -2 , T = 70 • C) but suffer compositional changes at the nanoscale. In the first hours of operation, the dissolution of Co atoms at their surface yields to the formation of a Pt-enriched shell covering a Pt-Co alloy core ("Pt-skeleton") and increases the affinity of the surface to oxygenated and hydrogenated species. This structure does not ensure stability in PEMFC conditions but is rather a first step towards the formation of "Pt-shell/Pt-Co alloy core" structures with depleted Co content. In these operating conditions, the Pt-Co/C specific activity for the ORR varies linearly with the fraction of Co alloyed to Pt present in the core and is severely depreciated (ca. -50%) after 1124 h of operation. This is attributed to: (i) the decrease of both the strain and the ligand effect of Co atoms contained in the core (ii) the changes in the surface structure of the electrocatalyst (formation of a multilayer-thick Pt shell) and (iii) the relaxation of the Pt surface atoms.