NaCl-templated synthesis of soybean-derived nitrogen-rich mesoporous carbon material: iron phthalocyanine integration for four-electron oxygen reduction

Abstract

The performance efficiency of fuel cells and metal–air batteries mainly depends on the cathodic oxygen reduction reaction (ORR). In this work, soybean-derived mesoporous carbon is synthesized by the carbonization of soybean powder using an inexpensive template, NaCl which creates porosity as well as limits the vaporization of heteroatoms by generating a protective layer. Soybean powder carbonized at 950 °C (SN950) shows high catalytic activity towards ORR in basic medium. To further enhance the ORR activity, iron phthalocyanine (FePc) was immobilized on the soybean-derived carbon and the resulting material is represented as FePc@SN950. FePc@SN950 and other control samples were characterized by Fourier-transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, Brunauer–Emmett–Teller analysis, and X-ray photoelectron spectroscopy techniques. FePc@SN950 shows an onset potential (E_onset) of 0.97 and 0.77 V (vs. RHE) and half-wave potential (E_1/2) of 0.92 and 0.70 V (vs. RHE) in basic and acidic media, respectively. Selectivity and percentage formation of H₂O₂ of the materials are measured by hydrodynamic experiments. The number of electrons transferred is found to be 3.5 and 3.8 in basic and acidic media, respectively. The selectivity for the formation of water was evaluated as 80% and 94% respectively in the basic and acidic media throughout the ORR region. The stability and durability of the material are checked by amperometry and cyclic voltammetry (CV) methods, where there are no significant changes in the current and E_onset values after 10 000 s and 3000 CV cycles respectively, in both acidic and basic media. Therefore, it is demonstrated that the synthesized SN950 has a large potential to replace conventional catalytic supports (like graphene, carbon nanotubes, and carbon fiber). FePc@SN950 could be used as a potential candidate to replace Pt-based catalysts in fuel cells and metal–air batteries.