High temperature polymer electrolyte membrane fuel cell degradation provoked by ammonia as ambient air contaminant

Abstract

High temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) are used from stationary to mobile applications and have the advantage of increased tolerances against fuel impurities like H2S and CO. However, air impurities can limit their performance and durability. Here, the impact of NH3-contaminated air is studied during 500 h of operation. 10 ppm NH3 in air provokes a voltage decay of at least −279.3 μV h−1 compared to −18.1 μV h−1 during operation without NH3 demonstrating strong sensitivity of the HT-PEM technology to this air pollutant. Cyclic voltammetry shows a selectively poisoned catalyst, whereby the loss of electrochemical surface area seems to be of no importance. Impedance spectroscopy reveals affected electrode charge transfer processes and strongly affected proton conductivity. μ-computed tomography illustrates significant membrane thinning being significantly larger compared to the blank reference cell. Ion chromatography further indicates that ammonium is incorporated into the cell, so that ammonia is believed to trap the protons stemming from phosphoric acid and hydrogen oxidation reaction. In conclusion, HT-PEMFC degradation caused by ammonia naming formation and incorporation of ammonium species and formation of nitrogen species interacting with the catalyst are identified.