Probing high catalytic activity and selectivity of enzyme-mimicking single-atom catalysts formed by pyrrole-type M-N4 sites embedded into g-C3N4 for oxygen reduction reaction

Abstract

Oxygen reduction reaction (ORR) is a vital half-reaction for fuel cells, zinc–air battery, and the synthesis of H2O2. Inspired by the mechanisms of dioxygen activation by metalloenzymes, we study an enzyme-mimicking single-atom catalyst through embedding the pyrrole-type M-N4 single sites in the g-C3N4 substrate (named bio-SA-M/g-C3N4). Herein, the catalytic selectivity and activity of bio-SA-M/g-C3N4 are explored systematically using density functional theory methods. At first, the stability of bio-SA-M/g-C3N4 is evaluated and 21 catalysts with excellent thermodynamic and electrochemical stabilities are selected. Secondly, the adsorption behavior of reaction species on screened bio-SA-M/g-C3N4 is researched in detail. Thirdly, the selectivity of ORR is explored by estimating whether ΔG*O of catalyst is larger than 3.52 eV. Emphatically, based on the calculated ∆Gspecies values, bio-SA-Fe/g-C3N4 and bio-SA-Co/g-C3N4 have potential to be 4e− ORR electrocatalysts with the particularly low overpotentials of 0.36 and 0.45 V, respectively. The bio-SA-Zn/g-C3N4, bio-SA-Cd/g-C3N4, and bio-SA-Hg/g-C3N4 can be considered as good 2e− ORR electrocatalysts because their low overpotentials are respectively 0.29, 0.21, and 0.30 V. Ultimately, ICOHP can be regarded as a good descriptor to analyze the bond strength between catalyst and reaction species.