Pt Redistribution within PEMFC MEAs and its Consequence on their Performances

Abstract

International audienceIn this paper, we studied the durability of PEMFC MEAs after on-site operation in stationary conditions. Harsh anode and cathode active layer degradation was monitored for Pt, C, F elements by chemical (EDS, XPS) and physical (SEM, TEM) techniques. At the cathode, Pt corrodes into Ptz⁺ species yielding severe redistribution within the MEA. Ptz⁺ dissolution and transport is favoured by activators/ligands (F or S-containing species resulting from the MEA polymers ageing, especially at the anode), which possibly act as counter ions. The presence of Ptz⁺ ions in the membrane favours chain-cutting and induces physical cross-links which modifies its thermo-mechanical, water uptake and conductivity properties. As a result, the risk of pinhole formation is greatly increased

Membrane and Active Layer Degradation upon PEMFC Steady-State Operation

“…However, a closer examination of Table II also reveals an increase of the sulfur content in aged cathode, which is consistent with the accumulation of Nafion membrane or ionomer degradation products ͑for instance, sulfonate groups ͑see Ref. 32 and Part II of the present paper͒ or SO 4 2 ͒. This is in line with previous observations of Xie et al 19,30 who detected sulfates anions by ion chromatography in the cathode exhaust water and more recent analysis of Teranishi et al 70 who detected H 2 SO 2 , and H 2 SO 3 by direct gas mass spectroscopy.…”

“…15,42,45,48 In addition to electrochemical/chemical corrosion of carbon, we point out possible chemical corrosion by radical species ͑OH•, HO 2 •͒ originating from the two-electron pathway of oxygen reduction reaction, 6,10,15,31,41,50,51 and subsequent Fenton-type reactions on Pt z+ species present inside the membrane upon aging. 32 Hydrogen peroxide species ͑amphoteric species͒ are likely formed at the anode potential by reduction of O 2 crossing over the PEM onto the anode Pt/C electrocatalyst. 52 Preferential corrosion at the electrocatalyst ͉carbon interface will yield weakly attached Pt nanoparticles, which are mobile over the carbon support and prone to agglomerate upon collision, 28,33 in agreement with the results from Table III.…”

“…31 Note that the presence of Pt z+ in the PEM 10 likely favors such radical formation from H 2 O 2 decomposition, as detailed in Ref. 32. The action of such radicals on the polymeric backbone likely yields HF or sulfate species.…”

Estudo de eletrocatalisadores nanoestruturados de Pt/C e Pt-Co/C depositados em carbono de alta área superficial: efeitos morfológicos e composicionais frente à reação de redução de oxigênio

“…Les catalyseurs les plus étudié à l'heure actuelle sont Pt/C et PtCo/C, mais ces matériaux nanostructurés ne sont pas stable en utilisation dans la PEMFC [16][17][18][19][20][21][22][23]. Etant donné que l'activité des électrocatalyseurs nanostructurés supportés sur carbone de grande aire développée change selon la structure, la morphologie et la taille des nanoparticules [2,[24][25][26][27][28][29][30][31], la dégradation à laquelle ils sont soumis en pile à combustible peut fortement modifier leur activité de RRO en cours de fonctionnement [1,20,22,[32][33][34][35]. Pt/C en fonctionnement en pile à combustible.…”