Degradation

Question 1

Name six degradation mechanisms.

Answer 1

Catalyst poisoning, catalyst agglomeration, membrane mechanical degradation, membrane chemical degradation, catalyst carbon support corrosion, membrane ionic contamination.

Question 2

Describe catalyst poisoning.

Answer 2

CO absorbed by platinum catalyst, causes less surface area, so decreased exchange current density.

Question 3

Describe catalyst agglomeration.

Answer 3

Platinum catalyst slowly joins together into larger particles, causes less surface area, so decreased exchange current density.

Question 4

Describe membrane mechanical degradation.

Answer 4

Peroxide produced rather than water, attacks membrane and reduces mechanical strength.

Question 5

Describe membrane chemical degradation.

Answer 5

Metal ions from bi-polar plate bond with the membrane, lose ionic conductivity.

Question 6

Describe catalyst carbon support corrosion.

Answer 6

During shutdown hydrogen/air mixing in anode causes low potential at cathode, which causes corrosion of the carbon supports, causing less surface area, so decreased exchange current density.

Question 7

Describe three degradation mitigations.

Answer 7

Don’t hold at OCV, or low voltage which starves the fuel cell of oxygen.
Minimise start/stop.
Minimise humidity cycling.