Sulfonic Acid Functionalization-Boosted Ultrafast, Durable, and Selective Four-Electron Oxygen Reduction Reaction: Evidenced by EC-SHINERS and DFT Studies#

Abstract

Hydroperoxyl intermediate is a vital component in the mechanism of electrochemical oxygen reduction reaction (ORR) and several other important chemical reactions. The selectivity and kinetics of ORR are controlled by the energetics of *OOH intermediate (* represents the active site). The present work integrates iron phthalocyanine (FePc) with sulfonic acid-functionalized multiwalled carbon nanotubes (MWCNTs-SO3H). The resulting composite (FePc@MWCNTs-SO3H) demonstrates significantly improved kinetics and higher four-electron selectivity for the electrochemical reduction of oxygen compared to its counterpart without functionalization (FePc@MWCNTs) in alkaline, neutral, and acidic media. Based on the in situ electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (EC-SHINERS) results and DFT calculations, it is proposed that sulfonate groups are involved in the water-assisted hydrogen-bonding interaction with the FeOOH intermediate. This interaction causes a substantial increase in selectivity and kinetics of ORR. Apart from the ORR, the findings of the current work strongly recommend that the functional groups on carbon support can be manipulated to get improved kinetics and selectivity of several important chemical transformations. © 2023 American Chemical Society.