A Simple Approach for Modulating the Active Site in Fe-Based Electrocatalysts

Abstract

Proton Exchange Membrane Fuel Cells (PEMFCs) have garnered attention as a next-generation, environmentally friendly energy solution to address issues like the climate crisis and depletion of fossil fuels resulting from excessive usage. Nevertheless, the commercialization of PEMFCs faces challenges due to the use of expensive platinum catalysts for the Oxygen Reduction Reaction (ORR). In contrast, Anion Exchange Membrane Fuel Cells (AEMFCs) offer advantages by utilizing cost-effective non-platinum catalysts, making ongoing research on non-platinum catalysts for AEMFCs essential. Numerous studies have been conducted to develop M-N-C catalysts in nanoparticle units using transition metals such as Fe, Co, and Ni for AEMFCs. Notably, Fe-based catalysts with FeNx active sites are considered representative candidates for AEMFCs. Moreover, recent research aims to advance Fe catalysts by incorporating single-atom active sites to enhance mass transfer and improve reaction efficiency at the atomic level.We have developed a straightforward method for synthesizing an Fe catalyst. The catalyst, synthesized through a redox reaction between aniline and a metal ion, followed by pyrolysis, exhibited remarkable durability and activity for the Oxygen Reduction Reaction (ORR). Notably, it possesses an active FeNx site crucial for ORR. Furthermore, by simply altering the solvent during the synthesis process, we observed a variation in the Fe-to-N ratio. Particularly noteworthy was the synthesis of Fe4N, which demonstrated activity for the Oxygen Evolution Reaction (OER). This synthesis method allows for the controlled manipulation of the catalyst's chemistry by varying the solvent, resulting in the production of Fe-based catalysts with either FeNx or Fe4N active sites, active for ORR and OER, respectively. To understand the catalyst's characteristics based on the solvent used during synthesis, we conducted a comprehensive characterization using techniques such as Thermogravimetric Analysis (TGA), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The electrochemical activity was investigated through a half-cell test, and efforts were made to interpret the results based on the catalyst's properties.