Artifacts in measuring electrode catalyst area of fuel cells through cyclic voltammetry

Cyclic Voltammetry (CV) is a well-established technique to measure the electrochemically active surface area (ECA) of a catalyst in an electrode through hydrogen adsorption/desorption (HAD). In the field of proton exchange membrane fuel cells this method can be applied to scales ranging from rotating disc electrodes (RDE) to single-cell and even multiple-cell stacks where the working electrode (WE) is part of a membrane-electrode assembly (MEA). In this paper, it is shown for MEA tests that molecular hydrogen evolution can create significant artifacts in the shape of the HAD curve, which impacts the calculated ECA. This artifact is related to the rate of mass transfer of molecular hydrogen away from the WE and depends on the nitrogen purge flow rate used for the WE during the voltage sweep. A brief discussion of spatially resolved CV measurements is also provided where it is shown that this same artifact can create the appearance of spatial variation in a cell's ECA. The impact of hydrogen evolution on ECA measurements can be mitigated by reducing the purge rate to below ca. 1 sccm/cm² of electrode active area, whereupon the ECA measured for an MEA agrees to that of the same catalyst in an RDE experiment to within 10-15%. Additionally, it is shown that the same ECA as measured for a catalyst in RDE can be obtained for an MEA-based one if the WE is filled with liquid water.