Study on Degradation of the Pt-Ru Anode of PEFC for Residential Application (2): Analyses of the MEAs Degraded in the Anode Performance

Abstract

Significant decrease in the voltage and increase in H 2 gain were observed after the low current density operation. However, recovery in voltage and decrease in H 2 gain were also observed by the dry treatment. The impedance of degraded MEA just after the low current density operation increased at the low frequency region in CO(10ppm)/H 2 (balance). On the other hand, the impedance of MEA that the H 2 gain was increased by long term operation for more than 20,000 h was increased at higher frequency region in CO(10ppm)/H 2 (balance). It was concluded that the increase of impedance was caused by the flooding in the anode in the first case, and by the essential degradation by Ru dissolution from anode catalyst in the later case.

Durability of Electrocatalysts in Polymer Electrolyte Fuel Cells

“…It has been also reported that flooding of the anode increases the local concentration of CO in the micropores of the anode, and greatly enhances CO-poisoning at the anode (20). The sudden drop of CO tolerance shown in Fig.…”

Study on Degradation of the Pt-Ru Anode of PEFC for Residential Application (3): Interpretation of AC Impedance Analyses of MEAs and the Nature of CO Poisoning on Anode of PEFC

“…1 (b), is well agreed with the calculated resistance using Eq. [2] at higher H 2 concentration, but much higher than the calculation at lower H 2 concentration. This discrepancy might be caused by actual diffusion control due to low H 2 concentration.…”

“…Therefore, if pure H 2 is used as fuel gas, E is independent of U f , and so the second impedance in Eq. [2] doesn't appear. On the other hand, at low U f or under so called "differential cell" conditions, both f U E ∂ ∂ / and i U f ∂ ∂ / become small, therefore, the second impedance is also negligible.…”

“…The MEA samples used in this study were same as those in the previous papers (1,2) except for "pure Pt" anode MEA which contained only 0.3 mg/cm 2 Pt in each electrode. Experimental apparatuses and procedures were also same as in the previous papers (1,2).…”

Establishment of Accelerated Degradation Method of PEFC Stacks (NEDO Project: Fundamental Research of Degradation of PEFC Stacks)

“…From the fundamental researches, it was found that the anode potential shifted to 0.8 V vs. RHE at a local area by the inhomogeneous composition of gas on the cathode while the H 2 was feed to anode continuously 1) , and Ru around the surface area of catalyst disappeared by hundreds of thousands times potential cycling in the potential range 0.05 ~ 0.4 V vs. RHE 2) . In addition, it was clarified that the flooding in the anode affected the CO tolerance performance 3) . And, the quantitative model of CO poisoning characteristic was proposed 4) .…”