Simultaneous impedance measurements elements of a running cell stack in EC-Lab Express (EIS pack) – Battery – AN. 16Latest updated: August 31, 2021
In this application note, the use of simultaneous EIS measurements on elements of a PEM fuel cell stack is demonstrated using a Bio-Logic VMP3. Impedance measurements on different cells within a stack under load can be useful, for example, to determine the internal resistance of each cell or if there is a problem with gas distribution within the stack. With special cables and several different booster options, the VMP3 or VSP can be configured to evaluate stacks of up to 20 elements of 100 cm2 surface area using a special galvanostatic electrochemical impedance spectroscopy (GEIS) technique.
Electrochemical generators such as primary and secondary batteries, fuel cells (FCs), and super-capacities are often composed of se-veral elements connected in a series. It is possible to connect dozens of these elements on FC stacks. The measurement of the potential difference on each cell allows the user to detect if there is a dysfunction on a cell, but does not give the reason why. On the other hand, impedance measurements on the different cells under a constant load can be useful, for example, to determine the internal resistance value or if there is a problem with the gas distribution in the stack [1-6].
Theoretically, an impedance meter alone is enough to carry out the successive scans of each cell. However, given the number of elements to scan and the fact that one measurement on a single cell can last over ten minutes, the system could drift in time. This might explain the fact that the impedance could be different from one cell to another. Also, the use of a multiplexer between the different cells and the impedance meter could be a source of artifacts.
The VMP3/Z multi-channel potentiostat and EC-Lab® enable the user to make these measurements simultaneously. This reduces the experiment time significantly.
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