Adapted Galvanostatic Charge Method for cell-individual in-situ characterization of PEM fuel cell stacks and systems☆

Increasingly challenging lifetime requirements for automotive Polymer-Electrolyte-Membrane (PEM) fuel cells call for onboard characterization methods to enable state-of-health (SOH) adaptive operation strategies. In this work, an adapted Galvanostatic Charge Method (GCM) is presented, that allows for cell-individual electrochemical characterization without nitrogen flush, making it system-and potentially onboard-compatible. Key innovation is to utilize the system's standard shutdown procedure, i.e. oxygen depletion with closed air valves, to create an inert atmosphere in the cathode volume in which the characterization takes place. The electrochemical processes triggered during the characterization with GCM are now embedded in a closed -volume-problem instead of a steady-flow-environment. This causes the hydrogen concentration difference between anode and cathode to be dynamic instead of constant during the characterization. In this work, a 0D-simulation model of the closed-volume-problem and complementary measurements on a system testbench are presented. Additionally, a novel model-based evaluation method is introduced which extracts the SOH -indicators electrochemical active surface area (ECSA), double layer capacity, hydrogen permeability of the membrane and short circuit resistance from the measurements by fitting simulated to measured voltage curves. The simulation model is thoroughly analyzed and a systematic error, evoked by the fluidic coupling of the individual cells, is found to influence the results obtained for membrane permeability. The influence of different initial conditions (among them initial hydrogen concentration) on the evaluation results is experimentally investigated and found to have no significant influence. For further studies, improvement potential was found in modeling, measurement procedure and evaluation method.

Automated summary

This work presents an adapted Galvanostatic Charge Method (GCM) for individual electrochemical characterization of automotive fuel cells without nitrogen flush. By utilizing the system's shutdown procedure, an inert atmosphere is created for characterization. A closed-volume-problem simulation model and complementary measurements are presented. A novel model-based evaluation method is introduced to extract state-of-health (SOH) indicators from the measurements. The study identifies improvement potential in modeling, measurement procedure, and evaluation method.