Spatially Resolved Electrochemical Impedance Measurement in a PEM Fuel Cell Using an Array of Reference Electrodes
Recently, an innovative reference electrode was developed at NPL that makes contact with the electrode of interest via a Nafion tube salt bridge inserted through the end plates of the cell . An ionic pathway through the gas diffusion layer is achieved by impregnating with Nafion at the point of contact. This gives a localised measurement of electrode potential and avoids the problems of ohmic drop and edge effects experienced by other reference electrode configurations. A significant advantage of the design is that commercial MEAs can be tested directly, with minimal modification to cell hardware. Using an array of these reference electrodes, a spatial map of electrode potential can be generated, as previously demonstrated during start-up/shut-down . Here we present the application of this reference electrode design to localised EIS measurement without the need for a segmented cell or complicated multiple frequency response analysis (FRA) equipment. The spatial variation in impedance in a commercial prototype single cell was mapped under a range of operating conditions using an array of reference electrodes and a single FRA with auxiliary voltage inputs. The advantages and disadvantages of this technique and the implications for modelling and optimisation of fuel cell design are discussed.
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