Measurement of Catalyst Layer Electrolyte Resistance in PEFCs Using Electrochemical Impedance Spectroscopy

Abstract

In this paper, electrochemical impedance spectroscopy ͑EIS͒ is used to resolve various sources of polarization loss in a pure hydrogen-fueled polymer electrolyte fuel cell ͑PEFC͒. EIS data are fitted to a fuel cell model in which the catalyst layer physics are accurately represented by a transmission line model. Extracted parameters include cell ohmic resistance, catalyst layer electrolyte resistance, and double-layer capacitance. The results showed that the catalyst layer electrolyte resistance for a stateof-the-art electrode ͑47 wt % Pt on Vulcan XC-72 carbon, 0.8 Nafion ͑1100EW͒-to-carbon weight ratio, 13 µm thick͒ at 80°C and fully humidified conditions was approximately 100 m⍀-cm 2 ; this translates to a dc voltage loss of about 33 mV at a current density of 1 A/cm 2 . Similar results were obtained for two experimental methods, one using H 2 ͑anode͒ and O 2 ͑cathode gas feed͒ and another with H 2 and N 2 supplies, and for two cell active areas, 5 and 50 cm 2 . The measured catalyst layer electrolyte resistance increased with decreasing ionomer concentration in the electrode, as expected. We also observed that the real impedance measured at 1 kHz, often interpreted as the ohmic resistance in the cell, can include contributions from the electrolyte in the catalyst layer.

Mechanistic Insights into the Oxygen Reduction Reaction on Metal–N–C Electrocatalysts under Fuel Cell Conditions

“…[32][33] The protont ransport resistance can also contributer emarkably to the total overvoltage of aP EFC, with R cath H þ at about 0.10 W cm 2 and 0.030 W cm 2 (À100 mV and À30 mV @1Acm À2 ,r espectively) for platinumbased standard catalystl ayers. [34,35] Eikerlinga nd Kornyshev have derived analytical expressions correlating the cathode catalystlayer structure/composition with the AC impedance response of PEFCs. [36] Among the special cases described in this model,t here is the proton transport resistance signature in the EIS spectrum,w hich appears as a4 5 8 straight line in the highfrequency domain, as clearly observed in the inset of Figure S2 (dashedline) and indirectly in Figure 2.…”

“…Meticulous care was taken to reduce the effect of cable inductance. [35] Cells were conditioned at the desired DC current for 60 sp rior to EIS experiments. The linearity of the current/ potential response was verified for every measurement.…”

DMFC electrode preparation, performance and proton conductivity measurements

“…The working electrode was fed humidified N 2 (60 sccm) and the cathode humidified H 2 (40 sccm). Using the same gas feeding conditions, R p values were obtained using electrochemical impedance spectroscopy (EIS) [1,[18][19][20]. The EIS spectra were collected at constant potentials and at frequencies between 50 kHz and 20 mHz applying a root mean square (RMS) voltage amplitude of 15 mV.…”

“…In the case of DMFCs, only a few studies [2,24] are available, hence, possible measurement procedures for R p are evaluated and discussed in this work. For PEM fuel cells, the measurement of R p has been well established [18][19][20]25]. The so-called ''H 2 /N 2 method'', combined with ac impedance spectroscopy, is typically used to measure the R p values in PEM fuel cells.…”

“…This method can be used after reaching PEMFC steady-state performance. The impedance of the catalyst layer is represented by a transmission line [1,[18][19][20]. An example of Nyquist plots obtained using the ''H 2 /N 2 method'' for MEAs prepared in this work, and used for R p measurements, is shown in Fig.…”