The effect of thermal treatment on structure and surface composition of PtCo electro-catalysts for application in PEMFCs operating under automotive conditions
Résumé
Structure and surface characteristics of carbon-supported PtCo cathode electro-catalysts were investigated to evaluate their performance and resistance to degradation under high temperature (∼110 ◦C) operation in a polymer electrolyte membrane fuel cell (PEMFC). Two different thermal treatments were investigated, i.e. 600 ◦C and 800 ◦C causing the occurrence of a disordered face-centered cubic (fcc) structure and a primitive cubic ordered (L12) phase. A specific colloidal preparation route and a carbothermal reduction allowed to obtain a similar mean crystallite size, i.e. 2.9 and 3.3nm for the catalysts after the treatment at 600 ◦C and 800 ◦C, as well as a suitable degree of alloying. Both electrocatalysts were subjected to the same pre-leaching procedure to modulate the surface characteristics. The surface properties were investigated by X-ray photoelectron spectroscopy (XPS) and low-energy ion scattering spectroscopy (LE-ISS, 3He+ at 1 kV).APt segregation in the outermost surface layers and similar electronic properties for the materials were observed. Both catalysts showed good performance under PEMFC operation; however, the catalyst characterised by the disordered fcc structure performed slightly better at low temperature (80 ◦C) and full humidification; whereas, the primitive cubic ordered structure catalyst showed superior characteristics both in terms of performance and stability at high temperature (110 ◦C) and low R.H. These operating conditions are more relevant for automotive applications. The enhanced stability of the catalyst characterised by primitive cubic ordered structure was attributed to the growth of a stable Pt-oxide layer during operation at high temperature and low R.H. hindering sintering and dissolution processes at the catalyst surface.
Domaines
Matériaux
Origine : Fichiers produits par l'(les) auteur(s)
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