The oxygen reduction reaction mechanism on Sn doped graphene as an electrocatalyst in fuel cells: a DFT study

Heteroatom doped graphene has caused particular interest in recent years due to its promising ORR (oxygen reduction reaction) activity in fuel cells. Sn doped divacancy graphene (Sn-Gra) was predicted to be a good candidate as a cathode catalyst in the previous study. In this work, the detailed ORR mechanism has been studied for Sn-Gra. The calculated charge transfer indicates that Sn and its adjacent four C atoms are the catalytic reaction sites. The unstable intermediate HOOH suggests that Sn-Gra experiences a four-electron ORR process. The most favorite pathway is the hydrogenation of the O-2 molecule. The rate determining step is the hydrogenation of OOH to form H2O + O with the energy barrier of 0.75 eV. This value is slightly smaller than 0.80 eV for Pt, implying that Sn-Gra is a potential cathode catalyst for ORR. The predicted working potential is 0.16 V for the most favorite pathway. We expect that this study could provide new insights for the design of low-cost and highly efficient electrocatalysts in fuel cells.