The large-scale commercial viability of fuel cell electric vehicles (FCEVs) requires a reduction of the platinum-specific power density (g_Pt/kW) from currently ca. 0.3 g_Pt/kW to levels of ≤0.1 g_Pt/kW [1]. This can only be accomplished by improving fuel cell performance at high current density (≥2 A/cm²) with membrane electrode assemblies (MEAs) containing ultra-low anode and cathode platinum loadings (<0.1 mg_Pt/cm²).

Owing to the fast hydrogen oxidation kinetics on platinum [2], anode loadings of 0.05 mg_Pt/cm² and below can be realized without significant MEA performance losses. On the other hand, large mass transport related voltage losses at high current density are observed when the cathode loadings are reduced to 0.05-0.10 mg_Pt/cm², which can be influenced by catalyst and electrode design [3]. In addition to optimization of catalysts and MEAs, the high current density performance is also affected by the diffusion medium, namely by the choice of substrate and the composition/design of the micro-porous layer (MPL) [4].

In this presentation, we will discuss various options for electrode and MPL design, illustrating their impact in 5 cm² single-cell differential-flow experiments. The measured voltage losses will be deconvoluted into kinetic losses based on data from H₂/O₂ measurements, into oxygen transport induced losses obtained from limiting current density measurements [5], and into contributions from the proton conduction resistance in the cathode electrode determined by AC impedance [6].

References

[1] O. Gröger, H. A. Gasteiger, J.-P. Suchsland, J. Electrochem. Soc., 162, A2605 (2015).

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

[3] A. Kongkanand, M. F. Mathias, J. Phys. Chem. Lett., 7, 1127 (2016).

[4] J. M. Morgan, R. Datta, J. Power Sources, 251, 269 (2014).

[5] D. R. Baker, D. A. Caulk, K. C. Neyerlin, M. W. Murphy J. Electrochem. Soc., 156, B991 (2009).

[6] Y. Liu, C. Ji, W. Gu, D. R. Baker, J. Jorne, H. A. Gasteiger, J. Electrochem. Soc., 157, B1154 (2010).

Acknowledgements: We gratefully acknowledge funding from the German Federal Ministry for Economic Affairs and Energy (BMWi) for the project “Optigaa2” (funding number 03ET6015E) in collaboration with Freudenberg as well as for the BMWi funded subcontracts with Greenerity GmbH and Umicore (project “HyMotion5-Brennstoffzellenstapel”).