Durabilty of Pt-Based Alloy Nanoparticles Supported on Functionalized Carbon Materials for the ORR – Tuning the Interaction between Particles and Support Material
Authors: Werheid Matthias , Weber Philipp , Weber Daniel Jochen , Janssen Marek , Oezaslan Mehtap 
Published: February 2020

In the last decades, proton exchange membrane fuel cells (PEMFC) have attracted large attention as promising renewable and clean technology for energy conversion. Designing nanomaterials with the aim to improve their electrocatalytic performance and long-term durability is still a critical challenge. Today´s PEMFC research has focused on Pt-based alloy nanoparticles combined with high surface area carbon materials due to its improved activity and stability for the ORR compared to pure Pt/C.[1,2,3] Although many studies have focused on the relations between the structural and chemical properties of the catalytically active metal nanoparticles and their catalytic ORR performance, the interactions of these nanoparticles with the carbon substrate have been rarely investigated up to date. In particular, the immobilization and stabilization of the nanoparticles on the support material have a strong influence on the long-term durability of the ORR catalysts. Therefore, one crucial point is the functionalization of the carbon support with hydroxide and carboxylate groups which seems to improve nucleation and dispersion of the Pt alloy nanoparticles; on the other hand, these oxygen-containing surface groups can accelerate the carbon corrosion associated with particle detachment during the potential cycling. Therefore, another strategy is the introduction of hetero-atoms as N-C-, C-B, C-F and C-S-bonds into the carbon framework improving their electrochemical oxidation resistance.[4,5,6,7]

One target of this work is the stabilization of the carbon support material by functionalization to prevent carbon corrosion under the operating fuel cell conditions. We modified the morphology, structure and chemical properties of the porous carbon materials by using different methods such as acid treatment or thermal treatment in a reactive gas atmosphere. On the other hand, we optimized the design of Pt-based alloy (Pt-Ni, Pt-Co) nanoparticles supported on these functionalized porous carbon support materials. The properties and behavior of these materials are monitored by using high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX) and X-ray absorption spectroscopy (XAS). The electrochemical stability and durability of the catalysts were also investigated by applying various accelerated test protocols such as potential cycling between 0.5 - 1.0 (10.000 cycles), 0.5 - 1.5 (2000 cycles) and 1.0 - 1.5 V vs. RHE (2000 cycles).

We monitored the electrochemically active surface area (ECSA) of the Pt and Pt alloy nanoparticles supported on these functionalized carbon materials during the runs to correlate its loss to the number of cycles, scan rate and potential range. Based on these results we evaluate the relationship between the carbon modification, size and chemical composition of the bimetallic nanoparticles, electrocatalytic properties and durability.

Based on this study, we developed a model, describing the critical parameters to improve the interaction between the particles and the support material. This approach serves to enhance the catalytic properties and long-term durability of the ORR electrocatalysts for PEMFC applications.

References:

[1] Hasché, F.; Oezaslan, M.; Strasser, P. Activity, Journal of The Electrochemical Society, 2012, 159, B25-B34.

[2] J. Zhang (Ed.), PEM Fuel Cell Electrocatalysts and Catalyst Layers: Fundamentals and Applications, Springer-Verlag, London, 2008.

[3] Oezaslan, M.; Strasser, P., Journal of Power Sources, 2011, 196, 5240-5249.

[4] N. Karthikeyan, B.P.Vinayan, M.Rajesh, K.Balaji, A.K.Subramani, S. Ramaprabhu, Fuel Cells, 2015, 15(2), 278–287.

[5] S. Sharma, B. G. Pollet, Journal of Power Sources, 2012, 208, 96-119.

[6] L. Li, L. Hu, J. Li, Z. Wei, Nano Research, 2015, 8, 418.

[7] F. Hasché, T.-P. Fellinger, M. Oezaslan, J. P. Paraknowitsch, M. Antonietti, P. Strasser, ChemCatChem, 2012, 4, 479-483.