Fuel starvation in automotive PEMFC stacks: stack current and bipolar plate resistance

Abstract Fuel cells are a viable option to reduce CO 2 emissions of the heavy-duty transportation sector. However, under certain operation conditions, individual cells in the fuel cell stack may suffer from an undersupply of hydrogen, called fuel gross starvation (FGS). The voltage of affected cells is then reversed, enabling subsidiary reactions to gain the necessary current. These reactions are known to cause oxidation of the carbon in the anode catalyst layer, leading to performance degradation. This study demonstrates that FGS situations may furthermore cause a detrimental overheating behavior at high stack current. The behavior of two different 20-cell fuel cell stacks is investigated towards fuel starvation of one contained cell. One stack used carbon bipolar plates (BPs) with a comparatively high electric sheet resistance. The other stack used a modified BP which contained a copper-inlay, resulting in low electric sheet resistance. The behavior of the intentionally fuel starved cell was inspected in form of locally resolved current density, temperature and cell voltage. Additionally, the voltage of all other cells was simultaneously measured at the fuel inlet and outlet. At low stack currents, the fuel starved cell showed well comparable local behavior for both stack types. Significant differences occurred with increasing stack current. A spatially equal negative voltage was observed for the fuel starved cell when incorporated in the stack with a copper-inlay in the BP. A very high heat generation resulted from this condition, and detrimental effects of overheating were observed. In contrast, the fuel starved cell showed an intense variation of the local voltage when incorporated in the stack with only carbon-based BPs. The fuel outlet region of this cell hereby obtained a negative voltage, but the fuel inlet region maintained a positive voltage. This phenomenon allowed the fuel starved cell to counter-act an excessive heat production.