Investigating the Durability of Unsupported Pt-Alloy Aerogel Cathode

Wednesday, 4 October 2017: 08:00
National Harbor 2 (Gaylord National Resort and Convention Center)
S. Henning (Electrochemistry Laboratory, Paul Scherrer Institut), H. Ishikawa (Panasonic corporation), L. Kühn (Chair of Physical Chemistry, TU Dresden), J. Herranz (Electrochemistry Laboratory, Paul Scherrer Institut), A. Eychmüller (Chair of Physical Chemistry, TU Dresden), and T. J. Schmidt (Laboratory of Physical Chemistry, ETH Zürich)
State-of-the-art polymer electrolyte fuel cells (PEFCs) require considerate amounts of carbon-supported platinum nanoparticle (Pt/C) catalysts (up to 0.4 mgPt/cm2MEA) to catalyse the cathodic oxygen reduction reaction (ORR) [1]. To reduce overall PEFC costs, these excessive Pt-loadings must be reduced by enhancing the catalysts’ ORR activity and stability; e.g. by alloying platinum with other metals like Ni, Cu, Co [2] and by replacing or completely removing the carbon support that suffers from significant corrosion during the normal operation of PEFCs [3].

To overcome these activity and stability challenges, unsupported bimetallic Pt-alloy aerogels consisting of a 3D nanochain network (~ 30 m2ECSA/gPt) were synthesized (see Figure 1 for a TEM image of Pt3Ni aerogel) [4, 5]. Both Pt-Ni and Pt-Cu aerogels meet the US Department of Energy ORR activity target for 2017 of 440 A/gPt at 0.9 VRHE[6] when tested in liquid half cells. Considering that this outstanding performance needs to be demonstrated in an actual PEFC, Pt‑Ni and Pt-Cu aerogels were processed into membrane electrode assemblies (MEAs) and characterized in a differential PEFC [7].

In this contribution, we present the MEA optimization process for unsupported Pt‑alloy aerogel ORR catalysts and compare cell performance and durability (start-stop cycles, load cycles) to a conventional Pt/C benchmark. To explain the outstanding stability of Pt-alloy aerogel catalysts for start-stop cycling (see Figure 1), catalyst layers were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX) at beginning-of-life and end-of-life.

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[4] S. Henning, L. Kühn, J. Herranz, et al., J. Electrochem. Soc. 163 (2016), F998-F1003.

[5] S. Henning, L. Kühn, J. Herranz, et al., Electrochim. Acta 233 (2017), 210-217.

[6] O. Gröger, H.A. Gasteiger, J.P. Suchsland, J. Electrochem. Soc. 162 (2015), A2605-A2622.

[7] P. Oberholzer, P. Boillat, R. Siegrist, et al., Electrochem. Commun. 20 (2012), 67-70.