DFT Studies of the Oxygen Reduction Reaction on Pristine and N-Doped Fe3C/Graphene Catalyst

Abstract

Proton exchange membrane fuel cells (PEMFCs) are considered to be a promising power generation systems for future mobile and stationary applications. One of the main factors that restrain their wide use is the sluggish kinetics of the oxygen reduction reaction (ORR) at the electrode. Platinum-based materials have been so far the most active catalysts for the ORR, but their high cost makes the technology rather exclusive. In recent years, a number of non-precious ORR catalysts have been reported [1-3]. Among them, a catalyst composed of Fe3C nanoparticles encased in graphitic layers [3] draws an increasing interest due to its high stability and activity, which may be a result of the presence of a new type of active site [4]. To explain this phenomenon, we study possible catalytic sites of Fe3C/graphene interface and its N-doped variant by means of the Density Functional Theory. Additionally we study other potentially interesting systems like Fe3C with multiple graphitic layers and its N-doped variants, as well as FeN4 moieties embedded in the graphitic layers. Free energy diagrams of the 4- and 2-electron associative pathways are calculated. The aqueous environment is modeled by including several explicit water molecules. Catalytic activity and selectivity towards H2O is considered and compared with current state-of-the-art ORR catalysts. [1] E. Proietti, F. Jaouen, M. Lefèvre, N. Larouche, J. Tian, J. Herranz, J.-P. Dodelet, Nat. Commun., 2011, 2, 416. [2] G. Wu, K. L. More, C. M. Johnston, P. Zelenay, Science, 2011, 332, 443. [3] Y. Hu, J. O. Jensen, W. Zhang, L. N. Cleemann, W. Xing, N. J. Bjerrum, Q. Li, Angew. Chem. Int. Ed., 2014, 53, 3675. [4] J.-P. Dodelet, R. Chenitz, L. Yang, M. Lefèvre, ChemCatChem, 2014, 6, 1866. Figure 1