From Polymeric Precursors to Synergistic Catalysts: Heteroatom-Doped Fluorinated Carbon for Oxygen Reduction Reaction in Aluminum-Air Batteries

Abstract

Abstract. The advancement of effective oxygen reduction reaction (ORR) catalysts is vital for improving the performance of aluminum-air batteries. This study presents fluorine (F)-, nitrogen (N)-, and sulfur (S)-doped carbon catalysts synthesized through the pyrolysis of fluorinated polymer precursors, resulting in a synergistic combination of hierarchical porosity, improved electrical conductivity, and optimized dopant interactions. An amorphous carbon matrix with a higher density of defects and some localized graphitization, as shown by the D/G ratios, is confirmed by structural characterization using X-ray diffraction (XRD) and Raman spectroscopy. Porous, layered morphologies with partially graphitized lamellar structures are revealed by field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM) imaging, which aids in effective oxygen transport. Electrochemical studies demonstrate, with improved catalytic activity of the FCN and FCNS catalysts, the onset potential to be 1.07 V versus RHE and 1.09 V versus RHE, a half-wave potential of 0.74 V versus RHE and 0.77 V versus RHE, and a Jlim of 6.27 and 5.1 mA/cm2, respectively. The near-complete four-electron pathway with little peroxide formation is indicated by the transference number (n) for FCN and FCNS, which are determined to be 3.99 and 3.98, respectively. Both FCN and FCNS show better stability and catalytic efficiency than fluorinated carbon (FC), which is explained by fluorine's hydrophobic nature and the combined effects of several dopants. These findings highlight the feasibility of using carbon catalysts doped with fluorine, nitrogen, and sulfur as metal-free substitutes for ORR applications in aluminum-air batteries.