The Effect of the Reference Electrode Position on the Measurement of Half Cell Polarization in Proton-Exchange Membrane Fuel Cells

Abstract

In this experimental and numerical study we analyze the polarization of the electrodes in a PEM fuel cell system. In order to measure the anode and cathode potential with respect to the electrolyte potential, a dynamic hydrogen electrode (DHE) is used as reference electrode. Two fundamental configurations for integrating a DHE into the membrane electrode assembly (MEA) are investigated: In the first configuration, the DHE is contacted to the membrane within a circular gap in the cathode catalyst layer, which is called edge configuration. In the second configuration, the DHE is placed between two membrane layers, which is called sandwich configuration. Differences between the reference electrode setups can be ascribed to an inhomogeneous electrolyte potential distribution close to the edge of the electrodes as described in literature. Our 2D fuel cell model as published in an earlier article is used to investigate this effect. We show that it is not possible to detect the electrode polarization by use of a reference electrode in edge configuration. By use of the sandwich configuration, the polarization of the anode and cathode half cells can be measured independently.

Positioning of a Reference Electrode in a PEM Fuel Cell

“…Numerical calculations 4 have shown that the membrane potential at the RE is close to the potential of the working anode, i.e., 0. To explain this effect, calculations 4 were performed, assuming a very low in-plane proton conductivity of the membrane. Below, we will show that this effect arises, in fact, from the very large exchange current density of the anodic hydrogen oxidation reaction (HOR).…”

“…1a). This design is relatively easy to realize in polymer electrolyte fuel cells (PEMFCs) using a two-layer membrane with a platinum wire located between the layers 3,4 (Fig. 1a).…”

“…This makes it challenging to interpret properly the DC signal obtained from the wire tip; the half-cell polarizations can be obtained by means of impedance spectroscopy only. 4 The second option is to place the RE at one of the electrodes, at a certain distance L gap away from the aligned edges of the working electrodes (Fig. 1b).…”

“…4,7,10 Numerical calculations, however, provide neither parametric dependencies nor characteristic scales for the variation of in such systems. Below, we solve the problem for a PEMFC with a single-edge (semi-infinite) working anode and an infinite working cathode, exhibited in Fig.…”

Electrocatalytic performance of fuel cell reactions at low catalyst loading and high mass transport

“…An inappropriate perimeter-placed reference is sometimes used. 17,18 But most commonly, the ORR characteristics are simply assumed to dominate the signal to justify the use of a two-electrode setup, which appears reasonable given the higher exchange current density of the HOR. However, Kuhn et al 19 separated the contributions with a pseudo reference electrode sandwiched between the electrodes and found that the HOR impedance was not negligible under their conditions, but of the same order of magnitude across the entire cell impedance range.…”