In phosphoric acid (PAFC) and high-temperature polymer electrolyte fuel cells (HT-PEFC) concentrated phosphoric acid is used as the electrolyte. In PAFC the acid is imbibed in an inert silicon carbide matrix while in HT-PEFC polybenzimidazole (PBI) membranes are used. In PAFC, because there is no interaction between the matrix and the acid the phoshate anion has a finite transference number which “results in acid migration toward the anode of an operating cell and results in migration between cells” quote from [1]. In PBI based membranes the phosphoric acid is bound to the PBI and its mobility reduced, so it was expected that acid migration is suppressed. However, in past years it was shown that acid migration is also an issue in HT-PEFC and most probably a life time limiting process. As in PAFC, in HT-PEFC, strategies need to be developed to limit acid migration and thus improve durability. This requires fundamental work to better understand migration and the imbibition of the porous structures at the anode. Therefore the wetting behavior of the anode gas diffusion layers with phosphorc acid is characzterized in ex-situ and operando experiments by X-ray imaging.

Similarities and differences in acid management and it’s characterization in PAFC and HT-PEFC is discussed and the prospects for HT-PEFC in the large co-generation market for small (1 kW) systems is assessed.

[1] H.R. Kunz, ECS Transactions, 11, 1447-1460 (2007)