Evidence for the stabilization of FeN₄ sites by Pt particles during acidic oxygen reduction

While Fe-N-C materials have shown promising initial oxygen reduction reaction (ORR) activity, they lack durability in acidic medium. Key degradation mechanisms include FeN₄ site demetallation and deactivation by reactive oxygen species. Here we show for mainstream Fe-N-Cs that adding 1 wt.% Pt nanoparticles via a soft polyol method results in well-defined and stable Pt/Fe-N-C hybrids. The Pt addition strongly reduces the H₂O₂ production and Fe leaching rate during ORR, while post mortem Mössbauer spectroscopy reveals that the highly active but unstable Fe(III)N₄ site is partially stabilized. The similar H₂O₂ electroreduction activity of Pt/Fe-N-C and Fe-N-C and other analyses point toward a long-distance electronic effect of Pt nanoparticles in stabilizing FeN₄ sites. Computational chemistry reveals that spin polarization of distant Pt atoms mitigates the structural changes of FeN₄ sites upon adsorption of oxygenated species atop Fe, especially in high-spin state.