(244f) Investigation of Catalytic Activity of Fecunc Catalysts for Oxygen Reduction Reaction in Alkaline Medium with Gas Diffusion Electrode Half-Cell System

Non-precious metal catalysts (NPMCs) are promising alternatives to expensive platinum catalysts for the cathode of the fuel cell. The lower overpotential of ORR and less corrosive environment at alkaline conditions made NPMCs more attractive [1]. To achieve efficient ORR catalysis, there are two factors to be considered. First, the development of high porosity of the catalyst for the formation and accessible active sites (Fe-N_x) [2]. The other is the binding energy between active sites and oxygen intermediates, which can be controlled by active site modification of coordination environment, heteroatom doping, additional M-N_x sites, formation of metal nanoparticles, etc [3]. Following these strategies, the FeCuNC catalyst with superior ORR activity in an alkaline medium was prepared using SBA-15, a mesoporous silica template [4].

This study aims to investigate the catalytic behavior of FeCuNC at a wide potential range including kinetic and mass transport limiting regions for a profound understanding of ORR catalysis. First, the catalytic activities of FeCuNC were investigated using a rotating disk electrode (RDE) system. Although enhanced kinetics of FeCuNC (0.92 V @ 3 mA cm^-2) relative to FeNC (0.89 V @ 3 mA cm^-2) and commercial Pt/C (0.83 V @ 3 mA cm^-2) was confirmed at the high potential region, limitations of analyzing the mass-limiting region of the polarization curve still existed due to the low solubility (1.26×10^-6 mol cm^-3) and the diffusion coefficient (1.93×10^-5 cm² s^-1) of oxygen in 0.1 M KOH [5]. Therefore, a gas diffusion electrode (GDE) half-cell system was introduced to investigate the catalytic activity of FeCuNC in the mass-limiting region. GDE was used as a working electrode contacted with flow channels for oxygen gas supply. By controlling variables such as catalyst loading of GDE, ORR behavior could be investigated in a condition relatively similar to that of a real single cell rather than RDE. GDE half-cell could provide information about both the kinetics of the catalyst and the mass transport effect due to the pore structure more effectively. Analysis of the resistance component of GDE by electrochemical impedance spectroscopy enabled a more profound understanding of the cathode-specific resistance with NPMCs.

[1] N. Chen, Y. M. Lee, Prog. Polymer Sci., 113 (2021) 101345.

[2] S. H. Lee, J. Kim, D. Y. Chung, J. M. Yoo, H. S. Lee, M. J. Kim, B. S. Mun, S. G. Kwon, Y. -E. Sung, T. Hyeon, J. Am. Chem. Soc., 141 (2019) 2035.

[3] K. Wan, T. Chu, B. Li, P. Ming, C. Zhang, Adv. Sci., (2023) 2203391.

[4] J. G. Kim, J. Cho, S. Han, H. Lee, E. Yuk, B. Bae, S. S. Jang, C. Pak, J. Mater. Chem. A, 10 (2022) 5361.

[5] B. B. Blizanac, P. N. Ross, and N. M. Marković, J. Phys. Chem. B, 110 (2006) 4735.