Ionomer distribution control in porous carbon-supported catalyst layers for high-power and low Pt-loaded proton exchange membrane fuel cells

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Abstract

The reduction of Pt content in the cathode for proton exchange membrane fuel cells is highly desirable to lower their costs. However, lowering the Pt loading of the cathodic electrode leads to high voltage losses. These voltage losses are known to originate from the mass transport resistance of O2 through the platinum–ionomer interface, the location of the Pt particle with respect to the carbon support and the supports’ structures. In this study, we present a new Pt catalyst/support design that substantially reduces local oxygen-related mass transport resistance. The use of chemically modified carbon supports with tailored porosity enabled controlled deposition of Pt nanoparticles on the outer and inner surface of the support particles. This resulted in an unprecedented uniform coverage of the ionomer over the high surface-area carbon supports, especially under dry operating conditions. Consequently, the present catalyst design exhibits previously unachieved fuel cell power densities in addition to high stability under voltage cycling. Thanks to the Coulombic interaction between the ionomer and N groups on the carbon support, homogeneous ionomer distribution and reproducibility during ink manufacturing process is ensured.

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Fig. 1: Overview of experimental approach and surface characterization.
Fig. 2: Morphological and structural characterization of catalysts synthesized in this study.
Fig. 3: Correlation of NH3 heat treatment on thermal stability and ORR activity.
Fig. 4: Effect of N modification on ionomer distribution and performance in fuel cell.
Fig. 5: Evaluation of the stability of the N-modified catalysts under potential cycling protocol.

Data availability

The data supporting the findings of this study are available within this article and its Supplementary Information files, or from the corresponding author upon reasonable request. The Supplementary Information contains descriptions of methods, discussion on physicochemical characterization and the electrochemical characterization of as-prepared/conducted CO stripping, polarization curves, limiting current measurements and accelerated stress testing. It also includes Supplementary Figs. 112 and Supplementary Tables 18.

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Acknowledgements

This work was supported by the BMW Group. We also thank the members of FC Test Field, FC Technology Development and Technology Material Analysis of BMW Group for their support during fuel cell testing, MEA manufacturing and decal preparation.

Author information

A.O. conceived the project. S.O. synthesized all the samples. S.O. and A.O. carried out the MEA manufacturing, fuel cell experiments and data analysis. H.S. and B.A. contributed to material synthesis including ammonolysis. H.N.N. conducted and analysed XPS measurements. J.H. conducted and analysed nitrogen physisorption measurements. U.G. carried out SEM/STEM measurements. M.G. carried out TGA measurements. P.S. provided guidance and constructive ideas throughout the project to ensure the successful outcome of this project. All authors contributed to the discussion part, drew conclusions and participated in finalizing the text and figures.

Correspondence to Alin Orfanidi or Peter Strasser.

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