Fe-porphyrin carbon matrix as a bifunctional catalyst for oxygen reduction and CO₂ reduction from theoretical perspective

The oxygen reduction reaction (ORR) and carbon dioxide reduction reaction (CO₂RR) have attracted worldwide attention in order to solve the energy crisis and global warming. In this work, we have investigated the ORR and CO₂RR activity of Fe-porphyrin carbon material (FeN₄-C) by using the density functional method. The catalytic active sites are identified based on the charge transfer analysis and it is found that FeN₄ moiety and its adjacent eight C atoms are the active centre. ORR proceeds via a four-electron process. The OOH hydrogenation into O + H₂O is the most favourable pathway with the rate-determining step to be the formation of OOH. The energy barrier is 0.09 eV, much smaller than 0.56 eV for FeN₄ doped graphene and 0.80 eV for pure Pt. The predicted working potential is 0.52 V, larger than 0.35 V for FeN₄ doped graphene. For CO₂RR, CO₂ tends to be reduced to HCHO and CH₃OH with the limiting potential of −0.62 V. HCOOH is the minor product. In a word, the above results suggested that FeN₄-C is a promising bifunctional electrocatalyst for both ORR and CO₂RR.