1588
Anode Aging through Voltage Cycling Induced by H2‑Air Fronts during System Start‑Up and Shut‑Down

Thursday, 5 October 2017: 17:00
National Harbor 2 (Gaylord National Resort and Convention Center)
J. N. Schwämmlein, P. J. Rheinländer (Technical University of Munich), Y. Chen (Singapore Institute of Technology), K. T. Freyer, and H. A. Gasteiger (Technical University of Munich)
Proton exchange membrane fuel cells (PEMFCs) are proposed as clean alternative to the internal combustion engines in automotive applications.1 This, however, requires that PEMFCs are sufficiently durable and meet life-time requirements compatible with current systems. Start-up and shut-down (SUSD) of the PEMFC, conducted by passing a H2/air front through the anode compartment of the fuel cell is a critical ageing mechanism that limits PEMFC life-time.2 It is widely known that the cathode corrodes due to high potentials occurring in certain cell compartments while the H2/air front passes through the cell. This leads to carbon corrosion and ultimately to a collapse of the electrode structure (so-called cathode thinning). The damage on the cathode increases with the H2/air front residence time and the cell temperature during the SUSD event. Hence, mitigation strategies to reduce cathode damage during SUSD include minimizing the H2/air front residence time and stack temperature.3,4

While these and other mitigation strategies have largely reduced SUSD damage on the cathode, recent studies suggest that SUSD events might also lead to voltage losses due to anode degradation.4 Mittermeier et al. proposed that the potential cycling of the anode during H2/air front passage from ≈0 V (H2-filled) to ≈1 V (air-filled) might be the main reason for anode corrosion during SUSD. Since this degradation mechanism would scale with the number of H2/air front passages, its impact on the overall SUSD damage will become more pronounced as the cathode is protected by other SUSD mitigation methods (e.g., use of graphitized carbon supports, SUSD at low temperatures, short H2/air front residence times) and upon the implementation of ultra-low anode loadings (<0.05 mgPt/cm2).

Aim of this study is to characterize the SUSD induced anode degradation mechanisms and to quantify the extents of carbon support corrosion and the loss of electrochemical surface area (ECSA). For example, ECSA losses of anode and cathode upon extended SUSD cycles are shown in Figure 1a and b, respectively. Furthermore, we will examine the feasibility of an accelerated test to quantify anode SUSD degradation based on voltage cycling between ≈0 and ≈1 V under N2. Finally, based on these data, we will project the influence of anode SUSD degradation in the case of anodes with ultra-low Pt-loadings (< 0.05 mgPt cm-2) based on pure Pt or Pt-alloy anode catalysts.

Acknowledgments

The authors of this work thank David Fischermeier for preliminary tests in an early stage of this study.

References

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