Analysis of polarization curves to evaluate polarization sources in hydrogen/air PEM fuel cells

A step-by-step technique to evaluate six sources of polarization, mainly associated with the cathode, in hydrogen/air proton exchange membrane fuel cells is demonstrated. The six sources of polarization were nonelectrode ohmic overpotential, electrode ohmic overpotential, nonelectrode concentration overpotential, electrode concentration overpotential, activation overpotential from the Tafel slope, and activation overpotential from catalyst activity. The technique is demonstrated as applied in the analysis of hydrogen/air polarization curves of an in-house membrane electrode assembly (MEA) using hydrogen/oxygen polarization curves as a diagnostic tool. The analysis results are discussed at three cell temperature/relative humidity (RH)/oxygen partial pressure (po(2), atm) conditions at atmospheric pressure: 80 degrees C/100% RHanode/75% RHcathode/Po-2 = 0.136, 100 degrees C/70% RH/po(2) = 0.064, and 120 degrees C/35% RH/po(2) = 0.064, which represent a near fully-humidified, a moderately humidified, and a low humidified condition, respectively. At the higher temperature operating conditions the RH and po(2), decrease resulting in higher electrode ohmic resistance (0.020, 0.020, and 0.035 ohm cm(2), respectively), lower limiting current (2019, 1314, and 819 mA/cm(2), respectively), and lower onset current density for significant electrode concentration overpotential (80, 60, and 40 mA/cm(2), respectively). The technique is useful for diagnosing the main sources of loss in MEA development work, especially for high temperature/low relative humidity operation where several sources of loss are present simultaneously. (c) 2005 The Electrochemical Society. [DOI: 10.1149/1.1860034] All rights reserved.