Enhancing\nElectrocatalysis: Engineering the Fe–N<sub><i>x</i></sub>–C Electrocatalyst for Oxygen Reduction\nReaction Using Fe-Functionalized Silica Hard Templates

The availability\nof robust and accessible active sites in iron–nitrogen-carbon\n(Fe–N<sub><i>x</i></sub>-C) electrocatalysts is essential\nto optimize the oxygen reduction reaction (ORR), which is the main\nobstacle in the commercial realization of fuel cells. Herein, a modified\nhard templating method to develop efficient Fe–N<sub><i>x</i></sub>-C has been presented that not only ensured the generation\nof a porous architecture but also helped in the homogeneous distribution\nof Fe throughout the structure. First, silica nanoparticles (NPs)\nwere grown via the Stöber process and then functionalized atomically\nwith iron through two different types of silane chains, i.e., (3-aminopropyl)triethoxysilane\n(APTES) and N-(2-Aminoethyl)-3-aminopropyltriethoxysilane (EDTMS).\nThe Fe-functionalized silica simultaneously acting as a sacrificial\ntemplate as well as an iron source was then impregnated with nicarbazin,\nwhich was a carbon and nitrogen precursor. The dried mix was subject\nto pyrolysis (H1) followed by acid washing to dissolve silica templates,\nand then, again, it was subjected to another pyrolysis treatment (H2).\nAt each proceeding step, ORR activity in both acidic and alkaline\nmedia was improved and the samples obtained at the last stage (i.e.,\nH2) outperformed the other counterparts collected at the initial stages\nof the fabrication pathway. Eventually, the electrocatalyst developed\nusing EDTMS-type silane attached to silica NPs (E_FeNC_H2) demonstrated\nthe highest onset potentials of 990 mV vs RHE in alkaline media and\n862 mV vs RHE in acidic media. Moreover, the lower peroxide yield\nof E_FeNC_H2 signifying nearly direct 4e<sup>–</sup> ORR was\nattributed to the highest specific surface area (627 m<sup>2</sup> g<sup>–1</sup>) and the optimum combination of active moieties\ndispersed in the porous carbonaceous framework.