Due to high efficiency and environmentally friendly benefits, proton exchange membrane fuel cell (PEMFC) vehicles have widely received attention by automotive manufacturers. With many years of research and development, fuel cell technologies have gradually grown to a point of market introduction. However, cost and robustness are two major challenges that need to be overcome to enable commercial viability of fuel cells in automotive applications. Simplifying the controls hardware, algorithms and software through robust cell designs can reduce the cost and overall complexity of the system.

  There are a few operating stages¹ within a fuel cell system such as start/stop², anode/cathode starvation, and local anode starvation³ that need careful consideration in developing the controls systems. GM has developed a series of screening protocols to assess how these events impact the electrode performance. Anode dynamic hydrogen starvation can happen when the requested load is higher than the amount of hydrogen being fed to a single or a few cells in the stack. In this work, we have performed a detailed study to simulate these dynamic starvation events in a single cell and investigate the effects of such events on PEM fuel cell performance.

Single cells built with 53-cm² catalyst coated diffusion media (CCDM) membrane electrode assemblies (MEAs) equipped with a high-speed mass spectrometer (HSMS) on the anode side were employed for investigating the cell performance with gas evolution before, during, and after a short dynamic anode hydrogen starvation. Two levels of anode loadings (0.5X and 1X) were screened for their robustness against the undesired anode hydrogen starvation events.

 Figure 1 shows cell voltage and gas evolution profiles during anode hydrogen starvation from 0.2 A/cm² up to 0.6 A/cm² within 90 seconds at 80 °C. At 0.2 A/cm², the cell voltage was ~0.8V and the gas composition was N₂ and unreacted H₂. As the current density went up to 0.6 A/cm², the H₂ flow rate is insufficient for the current demanded,  and the cell voltage quickly dropped to ~-0.8- -1.0V, which initiated oxygen evolution reaction (OER) followed by carbon oxidation reaction (COR) as the cell voltage kept decreasing. The current density was switched back to 0.2 A/cm² when the cell voltage hit to -1.5 V. to prevent excessive / uncontrolled damage to the cell in a single event. Three events are shown in Figure 1 to observe the changes of OER and COR on the anode electrode. The peak areas of O₂ and CO₂ from gas evolution indicate that the OER deactivated while the COR was sustained to meet the current demand. Twelve events at two levels of anode loading were conducted in this test for evaluating the robustness of the anode and cathode electrodes.

In this presentation, we will discuss the test protocol to evaluate the robustness of anode electrode against anode hydrogen starvation. The results show that the anode was damaged with increased starvation events depending on starvation duration time, current demand, electrode loadings, and anode electrode materials. Results indicate that  a combination of anode electrode material development and engineering design is the best approach to addressing anode hydrogen starvation.  

Acknowledgement

 

                The authors would like to thank Dr. Manish Sinha for his helpful discussion on anode hydrogen starvation in a PEM fuel cell system.

  References

 1. P. T. Yu, W. Gu, J. Zhang, R. Makharia, F. T. Wagner, and H. A. Gasteiger, Polymer Electrolyte Fuel Cell Durability, F. N. Buchi, M. Inaba, and T. J. Schmidt, Editors, Springer, New York, NY, 2009.

 2. C. A. Reiser, L. Bregoli, T. W. Patterson, J. S. Yi, J. D. Yang, M. L. Perry, and T. D. Jarvi, Electrochem. Solid-state Lett., 8(6), A273, 2005.

 3. W. Gu, R. N. Carter, P. T. Yu, and H. A. Gasteiger, ECS Tran., 11(1), 963, 2007.

Figure 1. Cell voltage and gas evolution profiles during dynamic anode hydrogen starvation events. The anode starvation was set from 0.2 A/cm² up to 0.6 A/cm² without adding additional H₂. The anode flow rates were H₂: 94 cm³/min, N₂: 94 cm³/min while the cathode air flow rates were 353 and 1060 cm³/min at 0.2 and 0.6 A/cm², respectively. The cell test conditions were: temperature: 80 °C, anode/cathode relative humidity: 32%/32%, pressure: 150 kPa absolute.