Alkaline Stability of Anion-Conductive Ionomer Coated on a Carbon Surface

Abstract

Anion-exchange membrane fuel cells (AEMFCs) are promising technologies that allow the use of nonprecious metals as catalysts because the oxidation reduction reaction at the cathode occurs readily at the high pH of AEMFCs. However, the insufficient chemical stability of the anion-conductive materials in AEMFCs currently limits their development. We studied the chemical stability of the electrolyte in the catalyst layer of AEMFCs containing cationic dimethyl polybenzimidazole (mPBI). Although degradation was observed in an mPBI membrane under alkaline conditions, mPBI coated on a carbon support showed excellent alkaline stability. Because no glass transition temperature was observed for mPBI after coating on the support, the increase of chemical stability was probably associated with the decrease of polymer flexibility.

Anion Exchange Ionomers: Design Considerations and Recent Advances ‐ An Electrochemical Perspective

“…[55] Finally, alkaline degradation of AEI can also differ from that of the corresponding AEM, by the simple fact that the anion exchange ionomer is deposited on a carbon support. [117] Han et al reported that, while an mPBI film decomposes into small pieces by hydrolysis and ring cleavage after 24 h in 0.01 m KOH, the same polymer deposited on carbon nanotubes does not show any sign of degradation under the same conditions. [117] This discussion underlined the importance of focusing on the performance loss of the catalyst layer under operating conditions, rather than on the alkaline stability of the anion exchange ionomer.…”

“…Finally, alkaline degradation of AEI can also differ from that of the corresponding AEM, by the simple fact that the anion exchange ionomer is deposited on a carbon support. [ 117 ] Han et al. reported that, while an mPBI film decomposes into small pieces by hydrolysis and ring cleavage after 24 h in 0.01 m KOH, the same polymer deposited on carbon nanotubes does not show any sign of degradation under the same conditions.…”

“…reported that, while an mPBI film decomposes into small pieces by hydrolysis and ring cleavage after 24 h in 0.01 m KOH, the same polymer deposited on carbon nanotubes does not show any sign of degradation under the same conditions. [ 117 ]…”

“…[117] Han et al reported that, while an mPBI film decomposes into small pieces by hydrolysis and ring cleavage after 24 h in 0.01 m KOH, the same polymer deposited on carbon nanotubes does not show any sign of degradation under the same conditions. [117] This discussion underlined the importance of focusing on the performance loss of the catalyst layer under operating conditions, rather than on the alkaline stability of the anion exchange ionomer. Nevertheless, the extensive work that has been reported on the study on the ex situ alkaline degradation of anion exchange membranes can offer a guide to the design of stable AEIs and to the mitigation of alkaline degradation, in case it is observed to cause performance losses.…”