Selective Hydrogen Oxidation Catalyst for Reduced Startup/Shutdown Degradation in Low Temperature Fuel Cells

While the durability of proton exchange membrane (PEM) fuel cells in automotive applications has been improved significantly over the past decade, the durability of the catalysts and the catalyst supports during transient operating conditions is still a critical issue. One of them is the carbon support corrosion during fuel cell startup and shutdown (SUSD) cycles [1], for which various mitigations strategies have been considered, based either on system control approaches or materials-based solutions [2, 3, 4]. A promising approach would be the use of a selective anode catalyst, i.e., with high activity for the hydrogen oxidation reaction (HOR) and low activity for the oxygen reduction reaction (ORR) [5]. Such a catalyst would eliminate the ORR on the anode electrode during a H₂/air-front event (i.e., an SUSD event) and thus remove the source for the transient excursions of the cathode electrode to high potentials during SUSD.

In this study, we present a promising selective anode catalyst based on iridium. Iridium exhibits not only very high HOR activity (only »3 times lower than Pt [6]), but also has significantly reduced ORR activity compared to Pt. The much lower ORR activity of Ir compared to Pt is shown in Figure 1, where the same noble-metal loading results in a >200 mV lower cell voltage for the ORR on Ir compared to Pt. On the other hand, H₂-pump experiments showed that the HOR losses for the low-loaded Ir catalyst in Figure 1 only amounted to 14 mV losses at 1.5 A/cm²), in good agreement with theoretical calculated HOR losses [6]. Therefore, Ir shows promise as a possible selective anode catalyst, which might lower SUSD degradation.

Figure 1. H₂/O₂ polarization curves recorded in in 50cm² cell of MEAs with different cathode catalysts (20wt% Ir/C red line, 20wt% Pt/C black line) adjusted to 0.1 mg_metal/cm². anodes based on 0.4 mg_Pt/cm² using 50wt%Pt/C). Other conditions: stoich.=2/9.5; 150kPa_abs, 80^oC; RH_C=RH_A=66%.

In this study we will show that replacing the conventional Pt/C catalyst with Ir/C at the anode electrode, the SUSD degradation rate can be reduced by a factor of 3 compared to Pt/C- based anodes.

References

[1]   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 (2005) A273.

[2]   P. T. Yu, W. Gu, R. Makharia, F. T. Wagner and H. A. Gasteiger, ECS Trans.3(1) (2006) 797.

[3]   M. L. Perry, T. W. Patterson, C. Reiser, ECS Trans.3(1) (2006) 783.

[4]   S. D. Knights, K. M. Colbow, J. St-Pierre and D. P.Wilkinson, J. Power Sources 127 (2004) 127.

[5]   B. Genorio, D. Strmcnik, R. Subbaraman, D. Tripkovic, G. Karapetrov, V. R. Stamenkovic, S. Pejovnik and N. M. Marković, Nature Materials9 (2010) 998.

[6]   J. Durst, C. Simon, F. Hasché, H. A. Gasteiger, J. Electrochem. Soc. 162 (2015) F190.

Acknowledgements

This work has been supported by SolviCore GmbH and the German Federal Ministry of Economy (BMWi) within the HyMotion5 research collaboration.