Very strong interaction between FeN4 and titanium carbide for durable 4-electron oxygen reduction reaction suppressing catalyst deactivation by peroxide

Abstract

Catalyst–support interaction triggering biased electron flows between the catalyst and reactant has been studied for electrocatalysis. The interaction was limited to the interfacial region between the catalyst and support when nanoparticle catalysts, which are bulky from the viewpoint of atomic dimensions, were employed. To clarify and maximize the effects of supports, herein, we investigated the catalyst–support interaction of a molecular catalyst loaded on a support. Iron phthalocyanine (FePc) as the molecular catalyst for the oxygen reduction reaction (ORR) was loaded on a two-dimensional monolayer leaf of titanium carbide (1L-Ti₃C₂). The strong interaction between Fe of FePc and Ti of 1L-Ti₃C₂ developed via FeTi₂ coordination encouraged the square-planar structure of FePc to be concavely distorted. The electron-rich Fe-active site having extra electrons given by less electronegative Ti of Ti₃C₂ allowed the single-oxygen intermediate species (*O) to be readily protonated to *OH, moving the RDS to the desorption step having a lower free energy gap or kinetic barrier. As a result, the strong FePc–Ti₃C₂ interaction decreased the potential required for reducing oxygen and moreover completed the ORR via a four-electron (4e) process rather than the 2e ORR. The catalyst durability was also improved due to the absence of peroxide generated from the 2e process.