Ultralow Degradation Rates in HT-PEM Fuel Cells
Authors: Rastedt Maren , Pinar Francisco Javier , Wagner Peter , García Héctor R. , Steenberg Thomas , Hjuler Hans A. , Paidar Martin , Bouzek Karel 
Published: February 2020

Despite the advantages of high temperature polymer electrolyte fuel cells (HT-PEM FCs) over low temperature PEM-FC, like higher tolerances against CO, degradation rates are higher in comparison to LT-PEM fuel cells. The best published degradation rates, achieved with HT-PEM FCs so far, constitute 4.9 µV/h under pure hydrogen and air supply and an operating temperature of 160 °C [1-2]. Low temperature PEM fuel cells under optimal conditions and a working temperature of 75 °C show very low degradation rates of 1-2 µV/h [3].

Therefore, one of the most important tasks within the European project CISTEM (Construction of Improved HT-PEM MEAs and Stacks for Long Term Stable Modular CHP Units, GA-No. 325262) is, next to the development of a new HT-PEM fuel cell based Combined Heat and Power (CHP) technology, to realize degradation rates with values less than 4 µV/h. The test conditions have been defined by the FCH JU:

Single cell test with 25 cm²-MEAs

Constant current density: 0.3 A/cm²

Hydrogen and air supply (λ=1.5/2)

Temperature: 160 °C

Min. test duration: 2,000 hours

The tests have been performed with Dapozol®-G55 MEAs with thermally cured polybenzimidazole (PBI) membrane and Pt/C based electrodes (BoA1-MEAs), developed and provided by Danish Power Systems and delivered to the facilities of different partners. The distribution of new MEAs and testing at three different lab facilities under agreed identical operating conditions support and verify achieved degradation results perfectly. Electrochemical investigation with polarization curves have been performed at Begin of Life (BoL), every 1,000 hours of operation and at the End of Test (EoT). The characterization has been completed with ante- and post-mortem micro-computed tomography (µ-CT).

Several tests have been performed, three representatives are shown in Figure 1 and the corresponding degradation rates are listed in

Table 1. The average degradation rate of the long term tests presented in this work results in 1.7 µV/h and this value correlates with the average degradation rate of LT-PEM fuel cells [3].

To verify the influence of different test conditions on the degradation rates, these experiments have been compared with constant load (0.3 A/cm²) long term tests under different fuel and oxidant compositions, with different flow field designs (serpentine and grid flow fields) and performed with complete in-situ electrochemical characterization procedures (polarization curves, electrochemical impedance spectroscopy, cyclic voltammetry and linear sweep voltammetry). These investigations enable the determination of the best possible operating conditions for HT-PEM fuel cells to achieve ultralow degradation rates.

Figure 1:Voltage changes as function of time under hydrogen and air supply (λ=1.5/2.0) and degradation rates, 160°C, 0.3 A/cm², Dapozol®-G55-MEAs. Test at UCTP still in progress.

References:

1. S. Yu, L. Xiao, B.C. Benicewicz, Fuel Cells, 08, 3-4, 165-174 (2008).

2. T.J. Schmidt, J. Baurmeister, ECS Transactions 3, 1, 861-869 (2006).

3. F.A. de Bruijn, V.A.T. Dam, G.J.M. Janssen, Fuel Cells, 08, 1, 3-22 (2008).

Figure 1