Versatile Strategy for Tuning ORR Activity of a Single Fe N4 Site by Controlling Electron Withdrawing/Donating Properties of a Carbon Plane.
Replacement of Pt based oxygen reduction reaction (ORR) catalysts with non precious metal catalysts (NPMCs) such as Fe/N/C is one of the most important issues in the commercialization of proton exchange membrane fuel cells (PEMFCs) Despite numerous studies on Fe/N/C catalysts, a fundamental study on the development of a versatile strategy is still required for tuning the kinetic activity of a single Fe N4 site. Herein, we report a new and intuitive design strategy for tuning and enhancing the kinetic activity of a single Fe N4 site by controlling electron withdrawing/donating properties of a carbon plane with the incorporation of sulfur functionalities. The effect of electron withdrawing/donating functionalities was elucidated by experimentation and theoretical calculations. Finally, the introduction of an oxidized sulfur functionality decreases the d band center of iron by withdrawing electrons, thereby facilitating ORR at the Fe N4 site by lowering the intermediate adsorption energy. Furthermore, this strategy can enhance ORR activity without a decrease in the stability of the catalyst. This simple and straightforward approach can be a cornerstone to develop optimum NPMCs for application in the cathodes of PEMFCs.
Journal of the American Chemical Society