1 1 1 1 1 1 1 1 1 1 1 1 1

-pi-i-n-|-r i i -i—1 ill.

; £«„ = 0.657

Ee«, = 0.62V :

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■ . . . .

I , , , , I , , , . I . , . ,'

Figure 2 Current density as a function of time for cell operated with dry gases (Hj/air) at constant voltage. 50 cm2 cell hydrogen/air reactant gases at atmospheric pressure. Anode electrocatalyst loading 0.3 mg Pt/cmJ, cathode electrocatalyst loading 1.1 mg/cm*, Nation 112 membrane. Rcactant gas utilization - 95% for hydrogen and 50% for air.

Figure 2 Current density as a function of time for cell operated with dry gases (Hj/air) at constant voltage. 50 cm2 cell hydrogen/air reactant gases at atmospheric pressure. Anode electrocatalyst loading 0.3 mg Pt/cmJ, cathode electrocatalyst loading 1.1 mg/cm*, Nation 112 membrane. Rcactant gas utilization - 95% for hydrogen and 50% for air.

Current density, mA/cm2

Figure 3 Cell potential vs. current density plots for PEMFCs with different humidification schcmcs. 50 cm2 cell gases hydrogen/air reactants at atmospheric pressure, 50 "C. Anode electrocatalyst loading 0.3 mg Pt/cm3, cathode electrocatalyst loading 1.4 mg/cmJ. Rcactant gas utilization - 95% for hydrogen and 50% for air.

PEMFC Performance 02 Enrichment Another method of increasing the cell performance is to use oxygen enriched air. The oxygen enrichment can be achieved by using a gas separation membrane. Oxygen enrichment is particularly valuable when the rcactant gases are not humidi fied. Fig. 4 shows that when the oxygen content of the inlet air stream is close to 40%, the difference in PEMFC performance between dry and wet gases is minimal. Another advantage of oxygen enrichment is that it permits the operation of the PEMFC with the non-humidified reac-tant gases at a higher temperature than when using ambient air. By operation of the PEMFC at a higher temperature (say 80® C), its efficiency for the utilization of heat is increased and to some extent simplifies the heat removal sub-system.

Figure 4 Bénéficiai effccts of oxygen enrichment on H/air PEMFC performance for operation without humidification of reactant gases. 50 cm2 cell area reactant gases at atmospheric pressure, 50 °C. Anode elcctrocatalyst loading 0.3 mg/cm2, cathode electro-catalyst loading 1.4 mg/cm2. Reactant gas utilization - 95% for hydrogen and 50% for air.

Current Density, mA/cm2

Figure 4 Bénéficiai effccts of oxygen enrichment on H/air PEMFC performance for operation without humidification of reactant gases. 50 cm2 cell area reactant gases at atmospheric pressure, 50 °C. Anode elcctrocatalyst loading 0.3 mg/cm2, cathode electro-catalyst loading 1.4 mg/cm2. Reactant gas utilization - 95% for hydrogen and 50% for air.

Conclusions By modifying the method of PEMFC electrode preparation we were able to operate cells without external humidification of reactant gases at relatively high power levels. The restriction on the operating temperature imposed by the removal of the humidification system may be alleviated by supplying extra water to the hydrogen stream only. Further optimization of the structure of the electroactive layer is needed to improve the performance of self humidified PEMFCs. Increasing the oxygen content of the air stream may be energetically favorable for achieving higher power density of the PEMFC power plant.

Acknowledgments The financial support of the Office of Naval Research (contract #N00014-95-1-0114) is gratefully acknowledged. Experimental samples of GORE-SELECT™ fluor-oionomer composite membrane were provided by W.L. Gore&Associates, Inc. for a nominal charge to cover partial laboratory expenses under confidentiality agreement. GORE-SELECT™ is a trade mark of W.L Gorc&Associates, Inc.. References

1 H.P. Dhar US Patent No. 5,242,764 (1993) and No 5,318,863 (1994)

2 M.S. Wilson and S. Gouesfcld, "J. of Applied Electrochcm.", Vol. 22, p 1., 1992.

3 M. Uchida, Y. Aoyama, N. Eda, and A. Ohta, "I. Electrochcm. Soc.", Vol. 142, p. 463,1995.

4 S. Gamburzev, O.A. Vclcv, S. Srinivasan, and A.J. Appleby, 190th ECS Meeting, San Antonio, Texas, Oct. 6- 11,1996, Ext. Abstracts.

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