Clarification of Active Sites for Oxygen Reduction Reaction on Silver and Nitrogen Co-Doped Carbon Materials

The oxygen reduction reaction (ORR) is one of the most important reactions in both fuel cells and metal-air batteries [1]. ORR needs catalysis to lower the electrochemical overpotential for high-voltage output for these technologies and, so far, platinum (Pt) has been the main catalyst of choice. However, as the expensive, traditional Pt/C catalysts are not viable in the long term, much effort has been focused on heteroatom doped and non-precious metal catalysts [2]. Metal-nitrogen co-doped carbon materials have emerged as the main candidates for replacing the platinum-based catalysts. Among these materials, silver and nitrogen co-doped catalysts have proven to exhibit high electrocatalytic activity for the ORR in alkaline media. However, no clear understanding exists about the exact catalytic mechanism and rational design of these catalysts. In this work, we synthesized model catalyst of silver and nitrogen co-doped carbon (Ag-N-C) by using simple precursors. Silver phthalocyanine and multi-walled carbon nanotubes have been used for the one-pot synthesis of Ag-N-C material. The morphology of the catalyst was studied by the transmission electron microscopy and the surface elemental composition was examined with X-ray photoelectron spectroscopy (XPS). The catalysts‘ activity towards ORR in 0.1 M KOH is assessed using the rotating disk electrode (RDE) method and the results are compared to those of commercial Pt/C catalysts (Figure 1). The created Ag-N-C model catalyst reveal a highly enhanced activity via the synergistic, doubly beneficial effects of the support material and formed catalytic centers, which were studied by density functional theory (DFT). Our theoretical calculations, which matched with the experimental findings, provide necessary hints on ORR mechanistic issues on the developed Ag-N-C model catalyst and will guide how to design and prepare better active non-Pt catalyst materials for fuel cell and metal-air battery electrodes, as well as providing deeper insight into the ORR mechanism occurring on this type of catalysts. References [1] M. Shao, Q. Chang, J.P. Dodelet, R. Chenitz, Recent Advances in Electrocatalysts for Oxygen Reduction Reaction , Chem. Rev . 116 (2016) 3594-3657. [2] K.M. Villemson, K. Kaare, R. Raudsepp, T. Käämbre, K. Šmits, P. Wang, A.V. Kuzmin, A. Šutka, B.A. Shainyan, I. Kruusenberg. J. Phys. Chem. C 123 (2019) 16065-16074. Figure 1