Experiment Study on the Current Density Distribution of PEMFC by Segmented Cell Technology

The transient response of proton exchange membrane fuel cells (PEMFCs) is one of the crucial factors for cell performance and automobile application. Even though the transient response of the overall current shows few oscillations, different local transient responses exist. And limited experimental research focuses on the local transient response of PEMFCs, which gives a significant understanding of the internal behavior of the cell.

In this study, the current overshoot and undershoot of a fuel cell with an active area of 108 cm² are investigated by segmented cell technology based on printed circuit boards. And a single PEMFC with parallel flow fields in bipolar plates that are matched with a self-designed stack is adopted. The performance of PEMFCs is tested by a 1kw fuel cell test station. The fuel cell operates in constant voltage mode under different stoichiometries, backpressures, and humidity conditions. When the cell voltage stabilizes at the set value, the total and local transient current signals are obtained by varying the voltage. After each experiment, dry nitrogen is pumped into the fuel cell to remove the liquid water in the flow channels. During the experiment, an electrochemical workstation monitors the changes of high-frequency impedance（HFR）of the total cell, and the local current density is collected using the NI cDAQ system controlled by the Labview platform.

The result shows that the phenomenon of current overshoot is more apparent than undershoot when voltage changes, but both of them can be significantly reduced when gas is fully humidified. The HFR results also confirmed that the transient fluctuations are strongly related to the hydration state of the membrane. With a higher air stoichiometry, the fuel cell shows better performance, faster transient response, and more uniform current distribution. Increasing the back pressure can improve the overall performance of the fuel cell, while the transient response keeps constant and the local stability decreases. As the total polarization curve stabilizes, it is also found that the phenomenon of overshoot or undershoot occurs due to the non-uniform behavior of PEMFC. The magnitude of current fluctuation in the inlet region is higher than the average value when the voltage decreases, while it has the opposite behavior when the voltage increases. And the current response in the middle area has an irregular pattern due to the coupling effect of the membrane hydration and oxygen concentration. In all cases, the transient behaviors near the outlet parts are the worst because of water flooding and low gas concentration. With the spatial current distribution data, the transient response and local stability are investigated in the comprehensive process of parameter comparisons. Moreover, the performance of fuel cell can be enhanced based on the results mentioned above, and optimal strategies can be proposed as a consequence of all the above considerations. The results can also provide an experimental basis for subsequent research on the dynamic response process of the stack.