Role of Nitrogenated Carbon Support in Porous Structure Formation of Pt-CeOx Based Catalysts
Authors: Novakova Jaroslava , Dubau Martin , Fuka Simon , Duchon Tomas , Veltruska Katerina , Johanek Viktor , Fiala Roman , Matolinova Iva , Potin Valerie 
Published: May 2020

Fuel cells (FCs) are on the path to become a viable technology of clean and efficient power in the upcoming future. Especially, hydrogen-fueled Proton Exchange Membrane Fuel Cells (PEMFCs) are on the rise of practical applications. Yet, several factors limit the extensive commercialization of these FCs. The main obstacle is the high cost of platinum that is by far the most effective element used for FC catalysts. In addition, the short lifetime of FCs due to the degradation of the catalyst support and the catalyst itself is also a severe constraint. It is essential to overcome these limitations, and thus, the catalyst-support interface is of our primary concern for good FC efficiency.
Herein, we deal with the study of cerium oxide (CeOx)-based catalyst enriched by platinum deposited on nitrogenated carbon (CNx) support via magnetron sputtering in an oxygen/argon atmosphere. The chosen method of preparation, magnetron sputtering, constitutes a fast and inexpensive way of preparing the high-surface-area nanostructured catalytic film [1]. The model studies of planar samples focused on variations of morphology and structure of Pt-CeOx layer due to the presence of the carbonaceous interlayers with different compositions are demonstrated in Fig. 1 by using Transmission Electron Microscopy (TEM). While for amorphous carbon (a-C), the slightly porous columnar structure is observed (Fig. 1a), in the case of CNx interlayer (Fig. 1b), the surface morphology is modified into the form of individual needles. Spectroscopy techniques, namely X-ray Photoelectron Spectroscopy and Electron Energy Loss Spectroscopy, reveal an important role of nitrogen incorporated in the CNx interlayer that enables formation of very porous surface structures. The model system with the largest achievable surface is chosen as a pattern for further improvement of the commercially available gas diffusion layer (GDL). By applying the CNx thin interlayer on top of the GDL support (Fig. 1d), the surface area of the Pt-CeOx catalyst is enlarged (Fig. 1e and f), as it is visible by Scanning Electron Microscopy (SEM) and TEM. In addition, it is demonstrated that tuning of catalyst film morphology provides a viable strategy towards higher performance in the PEMFC tests (Fig. 1g), complemented by better corrosion resistance of CNx interlayers under the start-up conditions of fuel cells [2].
Fig. 1 TEM cross-sectional micrographs of Pt-CeOx layers on the carbonaceous interlayers supported by a silicon substrate: CeOx /a-C (a), CeOx/CNx (b) and CeOx/CNx/a-C (c). SEM images of the GDL substrate coated by the CNx interlayer (d) and after the Pt-CeOx deposition (e), TEM side-view image of the Pt-CeOx/CNx/GDL system (f). Fuel cell performance as a function of the Pt concentration for the Pt-CeOx catalysts supported by the GDL substrate and the GDL substrate coated by the CNx interlayer (g).
The authors acknowledge the financial support from the Czech Science Foundation (grant No. 18-06989Y).
[1] I. Khalakhan, et al. Ceram. Int. 39 (2013) 3765–3769.
[2] J. Novakova, et al. Appl. Surf. Sci., submitted.

Figure 1