Fig. 4
Reaction mechanism involving water activation. a Schematic illustration of the proposed synergistic mechanism of ORR on MCS, featuring the dissociative reduction of O2 at the Mn site, the proton mediation by the Co site, and the surface proton transfer in between (reactions I and II). Inset central: DFT-calculated energy barriers for reactions I & II on MCS (100) (See Supplementary Tables 7 and 8 for details). Inset upper-right: DFT-calculated bond energies of O–H in H2O and Co-OH2. b Results of in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) studies for MCS and Pt electrodes in Ar or O2 saturated KOH solutions. See Supplementary Fig. 14 for relevant FTIR spectra. The IR signals of interest were from the bending vibration of H2O (inset). The Stark effect (wavenumber shift with potential) is a measure of the H2O adsorption on the surface. c Local density of water on MCS (100) and Pt (111) surfaces at 300 K, obtained from atomistic molecular dynamics (MD) simulations (also see Supplementary Fig. 15). Inset: Snapshots of water molecules in a surface layer up to 0.3 nm thick
