Electron Transfer and Catalytic Mechanism of Organic Molecule-Adsorbed Graphene Nanoribbons as Efficient Catalysts for Oxygen Reduction and Evolution Reactions

Adsorption of organic molecules onto graphene can tune the electronic structure of graphene, providing a simple approach to tailor electrochemical properties of graphene for catalytic applications. Graphene sheets adsorbed with tetracyanoethylene (TONE) molecules were studied using first-principles calculations to predict their catalytic activities for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in fuel cells and metal air batteries. The electronic structures and reaction free energies were calculated to analyze effect of electron transfer between graphene and TONE on the catalytic mechanisms of the graphene. Stone Wales defects and edges were also introduced into the models to understand their role in catalysis. The results show that TCNE-adsorbed graphene has a lower limit of overpotentials of 0.425 V for OER and ORR, comparable to that of noble metals and S-doped graphene. The most active sites locate at the edges of the graphene. Stone Wales defects enhance the catalytic activities on graphene nanoribbons. Our calculations predict that TONE-adsorbed graphene could be an efficient metal-free catalyst for ORR and OER.