Detection of Pt[sup z+] Ions and Pt Nanoparticles Inside the Membrane of a Used PEMFC

Abstract

The physical and chemical state of proton exchange membrane fuel cell ͑PEMFC͒ electrocatalysts ͑Pt/C͒ were investigated after 529 h of operation under fuel cell relevant conditions ͑333 K, 0.12 W cm −2 ͒ and 123 h of rest time under inert atmosphere ͑N 2 ͒. Upon aging, pronounced corrosion of the cathode electrocatalyst ͑carbon-supported platinum nanoparticles: Pt/C͒ was evidenced by field-emission gun scanning electron microscopy ͑FEG-SEM͒, high-resolution transmission electron microscopy ͑HRTEM͒, and electrochemical techniques. Carbon corrosion was witnessed by the decrease of the cathode thickness ͑−60%͒ and by the presence of nonsupported Pt particles inside the electrode. At the cathode, the corrosion of Pt nanoparticles produces Pt ͑*͒ z+ ions which diffuse in the ionomer phase or in solution ͓͑*͒ stands for ionic species present in the ionomer phase or in solution͔. These ions are highly mobile inside the membrane electrode assembly ͑MEA͒ and may cross over from the cathode to the anode through the PEM. The driving force for that is the electro-osmotic drag ͑if Pt ͑*͒ z+ ions combine with anions and carry a negative charge͒ and the chemical diffusion ͑concentration gradient of oxidized platinum species͒. Consequently, Pt ͑*͒ z+ ions were detected by ultraviolet ͑UV͒ spectroscopy in the PEM. Due to the high mobility of Pt ͑*͒ z+ ions, FEG-SEM and HRTEM analysis of the cross sections of MEAs revealed a pronounced change of Pt distribution after operation. Size distributions of both anode and cathode electrocatalysts evidenced an increase of the mean particle size, tailing toward large particle sizes and particle agglomeration. Nonspherical Pt nanoparticles were detected inside the PEM, the size and shape distribution of which strongly depend on the distance from the cathode. We believe Pt ͑*͒ z+ ions are reduced chemically inside the membrane by H 2 crossing over the PEM and both chemically and electrochemically at the anode/cathode.

Durability of Unsupported Pt-Ni Aerogels in PEFC Cathodes

“…Figure 4D) from a BOL value of ≈38 μm/(mg Pt cm −2 ) (or ≈33 μm/(mg C cm −2 ), which agrees with the 28 ± 2 μm/(mg C cm −2 ) reported in literature) 36 to ≈23 μm/(mg Pt cm −2 ) and points to a collapse of the CL structure which can inhibit effective mass transport of reactants and that is supported by the drastic performance decline in the H 2 /air I/E curves in Figure 2A. The CL collapse can be attributed to carbon support corrosion in the applied potential regimes [20][21][22]37,38 and the resulting CL porosity decrease has been demonstrated by Schulenburg et al 39 in a FIB-SEM tomography study. On the other hand, representative cross section images before/after the load-cycle AST (Figures 3D/3F) do not indicate significant morphology/porosity changes concomitant with the negligible decrease in thickness to ≈34 μm/(mg Pt cm −2 ) discernable from Figure 4B.…”

A review of polymer electrolyte membrane fuel cell durability test protocols

“…A variety of investigations into catalyst degradation have been conducted [63][64][65][66][67][68][69][70]. Catalyst ASTs described in the literature generally simulate duty cycle induced catalyst degradation by potential cycling from a lower potential, in the range of 0.1-0.7 V, to increased potential, such as OCV, 1.0, or 1.2 V. Some examples of these studies are given in Table 2.…”

Improving oxygen reduction reaction activity and durability of 1.5nm Pt by addition of ruthenium oxide nanosheets

“…In addition to the unsatisfactory ORR activity, there are also problems associated with performance loss with long term operation due to aggregation and dissolution of Pt particles and carbon corrosion [2][3][4][5][6][7]. Consequently, the activity and durability of Pt/C catalysts must both be improved for wide-spread commercialization of polymer electrolyte fuel cells [1,8].…”