Transition metal embedded graphynes as advanced bifunctional single atom catalysts for oxygen reduction and evolution reactions

Noble metals are well-known to be highly efficient for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, their scarcity and high price have severely hampered their large-scale commercial applications. In this work, with the aid of density functional theory calculations we systematically screened 26 types of transition metal atom embedded gamma-graphyne monolayer (TM-GY) as potential effective and cheap single functional and bifunctional single-atom catalysts (SACs) for ORR/OER. The catalytic activity of ORR/OER can be expressed by a single descriptor of the adsorption free energy of the OH intermediate. Our research shows that Fe, Ir, Co, Rh, Cu, Ni, Pd and Pt-GY are potential single-functional and bifunctional SACs candidates for ORR or/and OER. Specifically, Co-GY was found to be the optimal bifunctional SAC for ORR and OER. A three-step strategy for screening bifunctional SACs was put forward: (i) non-radioactive/toxic element, (ii) single-function SACs and (iii) bifunctional SACs.