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A Detailed Analysis of Internal Resistance of a PEFC Comparing High and Low Humidification of the Reactant Gases

Abstract:

Polymer electrolyte fuel cells (PEFCs) have shown a great potential to be used in several applications, e.g., portable, mobile and stationary systems. Each of the mentioned applications demands from PEFCs different operating conditions to perform in the best possible manner. Knowing in detail the behavior of their internal components will help to improve the mechanical and thermal properties of the different constitutive layers. The objective of this research is to analyze in detail the behavior of the internal resistances of a PEFC, using the impedance spectroscopy technique. A single cell is evaluated in a broad range of current densities, i.e., from 0.2 to 2.0 A.cm–2, to evaluate the resistances that cause loss of performance. The analyzed resistances correspond to the ohmic, charge transfer and mass transport resistance. The results were obtained after the interpretation of the data taking from Nyquist diagrams, and they were analyzed considering high and low conditions of relative humidity (RH). The obtained results showed that the ohmic resistance (attributed to membrane Nafion® 212), is independent of the load applied for fully humidified conditions, with a value of 0.0725 Ω.cm2. On the other hand, it is strongly dependent on low humidification conditions, with values between [0.198–0.132] Ω.cm2, for current density of [0.2–2.0] A.cm–2, respectively. It was also found that the charge transfer resistance decreases with respect to the applied load until a saturation value, and further it represents the major participation to the total resistance of the cell. The charge transfer resistance represents around 50–75% of the total resistance in conditions of high RH, and among 30–65% for conditions of low RH. In addition, it was found that the mass transport resistance appears early at low RH and triples for full humidification conditions.