(Invited) The Impact ofin-Situ Activation of a C-Coated Catalyst on the Performance and Durability in Proton-Exchange Membrane Fuel Cells
Authors: Hnyk Franziska Carmen , Lazaridis Timon , Astudillo Leonardo Isaias , Schilling Markus Achim , Pietsch Markus Ruben , Gasteiger Hubert Andreas 
Published: August 2024

Zero-emission electricity production for stationary or mobile applications can be realized by PEM fuel cells (PEMFCs), making it an important constituent for a renewable energy transition. Especially relevant in heavy-duty applications, a high power output at low current densities (related to a high mass activity, MA) under dry conditions is necessary to meet the efficiency targets.[1]

In general, mass activity of a Pt/C catalyst can be negatively affected by ionomer poisoning, which describes the adsorption of ionomer endgroups onto the active Pt surface. This effect is especially pronounced for platinum supported on so-called solid carbon supports (e.g., Vulcan – Pt/V)[2] and by operating a fuel cell at low relative humidity (RH).[3] In order to minimize performance losses due to ionomer poisoning, concepts exist to shield the Pt particle from the ionomer, e.g., by alkanethiol masking[4] or by Pt-overlayers of porous SiO2
[5] and carbon derived from dopamine coatings.[6] In the latter case, the authors observed that it was possible to decrease ionomer poisoning and increase MEA performance under dry conditions. However, the transport of reactants to the Pt active sites is hindered by the carbon-overlayer, resulting in inferior high current density (HCD) performance.
In this work, we developed multiple in-situ activation strategies for a carbon-coated Pt/V cathode catalyst, synthesized following an adapted protocol from Yamada et al.[6] Our results show that apart from a significantly improved MA, high current density performance is retained for an activated carbon-coated Pt/V (C-Pt/Vactivated, solid orange symbols in Figure 1). Compared to the Pt/V baseline catalyst (blue symbols), the MA can be increased by a factor of ~2 (C-Pt/Vactivated with im
0.9V = 248±9 A gPt
-1 and Pt/V with im
0.9V = 110±13 A gPt
-1) while simultaneously maintaining comparable high current density performance at 90% RH. However, as we will show, the beneficial effect of the activated carbon-coated Pt/V is particularly pronounced at operation under dry conditions, where C-Pt/Vactivated outperformed the Pt/V baseline over the entire current density range (e.g., by 80 mV at 1.7 A cm-2).
Furthermore, possible limitations in terms of durability of the C-overlayer used in this work will be discussed.

Figure 1: Differential-flow H2/Air performance at 80 °C/90% RH and 145 kPaabs for different cathode catalysts: baseline catalyst (Pt/V), C-coated Pt/V catalyst before activation (C-Pt/Vb
efore activation), and activated C-coated Pt/V catalyst (C-Pt/Va
ctivated). In the 5 cm2 active area single-cell, the catalyst loadings were 0.25 mgPt cm-2 and 0.05 mgPt cm-2 on cathode and anode, respectively; a 15 µm reinforced low-EW PFSA membrane was used.

References

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Acknowledgement

We gratefully acknowledge financial support from the Fuel Cells and Hydrogen 2 Joint Undertaking (JU) under the MORELife grant agreement 101007170 that enabled us to conduct these studies. The JU receives support from the European Union’s Horizon 2020 research and innovation programme and Hydrogen Europe and Hydrogen Europe Research.

Figure 1