Model Non-Precious Metal Catalysts for Oxygen Reduction Reaction: A Bottom-up Approach

Further development of non-precious metal catalysts (NPMCs) synthesized from earth-abundant elements (C, N, transition metal) continues to be challenged by the lack of understanding of the origin of the oxygen reduction reaction (ORR) activity from such complex materials. Current state-of-the-art synthesis methods for NPMCs involve intricate pyrolysis steps producing highly heterogeneous catalytic systems (1, 2). Therefore, a systematic bottom-up approach using model carbon systems needs to be developed for the better understanding of the formation of active sites and the active site identification.

Recently, we have reported a novel approach for the incorporation of nitrogen heteroatoms into the graphitic carbon structure of liquid-phase exfoliated graphite (3). This approach utilizes high-flux energetic neutral atom beam technology (ENABLE) to incorporate nitrogen heteroatoms via direct chemical activation overcoming thermal activation barriers. Our preliminary results have identified a relationship between the type of nitrogen species doped and the substrate temperature (Figure 1). However, although improved onset potential for the ORR was observed from thin films doped with 13 at.% nitrogen (87% graphitic), the electrocatalytic activity in acid electrolyte is still poor. The work to be presented in this talk represents the continuation of our efforts to understand the role of each component in NPMCs, this time with the addition of transition metals, Fe and/or Co, prior to nitrogen doping. Electrochemical studies will be performed in both acid and alkaline electrolytes to better understand the different reaction mechanism in both environments.

References:

1. G. Wu, K. L. More, C. M. Johnston and P. Zelenay, Science (New York, N.Y.), 332, 443 (2011).

2. E. Proietti, F. Jaouen, M. Lefèvre, N. Larouche, J. Tian, J. Herranz and J.-P. Dodelet, Nature Communications, 2, 416 (2011).

3. U. Martinez, T. L. Williamson, K. Artyushkova, N. Mack, G. M. Purdy, J. H. Dumont, D. Kelly, W. Gao, A. M. Dattelbaum, A. Mohite, G. Gupta and P. Zelenay, ECS Transactions, 64, 293 (2014).