The membrane electrode assembly (MEA) was constructed with Nafion 112 membrane. The

E-I

polarization curves and the electrochemical impedance spectrum (EIS) of the proton exchange membrane fuel cell (PEMFC) without external humidification were tested. By comparing with the EIS at 20 ℃ and 55 ℃， the test results indicated that there were obvious difference between R

hf

which represented the ionic resistance

and R

ct

which corresponded to the charge transfer resistance at these two different temperatures. The values of R

hf

under low current densities were consistent with the ohmic loss in PEMFC. The values of R

hf

and R

ct

increased with the increasing of the operating temperature when PEMFC was operated at 15 mA·cm

-2

. The value of R

hf

changed significantly with the increasing of temperature

which was the main factor that caused the breakdown of PEMFC operating over 45 ℃.