The technical possibility and possible issues of an intermediate–temperature–operated polymer electrolyte fuel cell (@120 °C, IT–PEFC) was investigated toward the launching of new fuel cell heavy–duty vehicles. Commercial perfluorosulfonic acid membrane (PSFA, NRE212) and a commercial Pt catalyst supported on carbon (Pt/C: TEC10E50E, TKK) were selected to clarify the possible issues in the fuel cells. The higher oxygen back–pressures, over 200 kPa_(abs.), allowed us to obtain higher power densities than those for cells operated at 80 °C (Fig. 1), because the water vapor pressure at 120 °C exceeded 100 kPa_(abs.) above 50% RH. The mass activity at 0.85 V increased monotonically with increasing back–pressure above the water vapor pressure of 160 kPa_(abs.) at 120 °C, 80% RH. The open circuit voltage (OCV) exceeded 1.0 V for back–pressures above 200 kPa_(abs) at the Pt loadings on the cathode catalyst layer above 0.20 mg_Pt cm^–2 (Fig. 2), which would relate with the hydrogen crossover in the PFSA membrane. The mass activity (@0.85 V) decreased moderately with decreasing cathodic Pt loading amount at each back–pressures (Fig. 3), indicating that the limitation of Pt mass activity in the lower Pt loading cathode catalyst layers occurred at 120^oC, 80 %RH. The load cycle durability test (0.60V-1.0 V, 6 sec.) of the Pt catalyst supported on carbon at 120 °C at low humidity (20% RH) was higher than that at 120 °C at high humidity (80% RH) and 80 °C at 80% RH (Fig. 4), indicating that effect of Ostwald ripening would mitigate. The degradation of PFSA membrane accelerated at open circuit voltage condition by increasing operating temperature despite of the operation under the high humidity condition of 80% RH. We propose that the further improvement of both the gas transport properties in gas diffusion layers and the durability of the PFSA membrane to realize the IT–PEFC operation.

Acknowledgment

This work was partially supported by funds for the project “Electrolytes, Catalysts and Catalyst layers with Extraordinary Efficiency, power and Durability for PEFCs-2040 (ECCEED’40) from the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

Reference

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