Evaluation of the Galvanostatic Charging Current Diagnostics for the In Situ Characterization of Aged MEAs in PEMFCs

Unlike in the case of single-cell proton exchange membrane fuel cells (PEMFCs), implementing voltage-controlled in situ diagnostics in PEMFC stack tests is challenging, as the single cell voltage cannot be controlled precisely. Consequently, in PEMFC stacks, current-controlled methods must be used. Here we evaluate the so-called charging current (CC) diagnostics for its suitability to quantify the electrochemically active surface area (ECSA) of a platinum-catalyzed electrode of a membrane electrode assembly (MEA) as well as the H₂-crossover (i_{H2− x}, memb) and the ohmic-shorting currents (i_{short, memb}) of MEAs. As the here proposed analysis method enables an independent quantification of both i_{H2− x}, memb and i short, memb, reliable ECSA values can be obtained not only for pristine MEAs but also for severely aged MEAs that exhibit low electrode roughness factors (rf) and significant H₂-crossover and shorting currents. This is validated using model MEAs with very low rf values and/or high H₂-crossover/shorting currents, characteristic for MEAs after accelerated stress tests (ASTs). The CC diagnostics was also applied to an automotive-scale short-stack (manufactured and tested at EKPO Fuel Cell Technologies) after ∼8000 h of a load-cycling AST. Finally, a brief guideline on how to conduct the CC diagnostics and its limitations for PEMFC stacks is presented.