NH3-plasma pre-treated carbon supported active iron-nitrogen catalyst for oxygen reduction in acid and alkaline electrolyte
Metal-Nitrogen-Carbon (M-N-C) catalysts synthesized by conventional high-temperature carbonization method are considered as promising electrocatalysts for oxygen reduction reactions. Herein, we proposed a new approach for the preparation of M-N-C catalysts through NH3-plasma pretreatment of high surface area black pearl carbon. In this study, pre-treated carbon support facilitated the formation of a Fe-N-C (FeNC/NH3-C) type model catalyst through pyrolysis, acid-treatment, and an additional pyrolysis step. In contrast to untreated FeNC/C, plasma pre-treated FeNC/NH3-C contains Fe3C and Fe-Nx as active catalytic sites. XPS confirms the presence of a high surface concentration of FeNx (43.6%) on FeNC/NH3-C that promotes low oxygen reduction overpotential (0.80 V vs. RHE in 0.5 M H2SO4 and 1.0 V vs. RHE in 0.1 M KOH). Hence plasma activates the surface and incorporates nitrogen, which forms stable Fe-N coordination for accelerating oxygen reduction. Importantly, FeNC/NH3-C shows lower peroxide yield at 0.6V vs. RHE (<1.0 % in 0.5 M H2SO4 and <2 % in 0.1 M KOH) that can reduce the detrimental effect of H2O2 on the catalysts support and exhibits high stability, seen from thousands of potential cycling stability tests of FeNC/NH3-C in acid solutions. Thereby this plasma-based new synthetic approach can promote more active and stable non-precious metal catalysts.