Alkaline earth metal based single atom catalyst for the highly durable oxygen reduction reaction

Abstract Developing nonprecious group single-atom catalyst (SACs) based on alkaline earth metal has been rarely explored. Mg metal hampered the catalytic activity towards ORR due to the strong bonding of active centers with oxygenated group intermediate, whereas N-bonded Mg atoms have optimal bonding strength with intermediate oxygen species by adjusting the p-band center position. The co-ordination environment of Mg-Nx plays very crucial role in exhibiting the excellent catalytic activity towards ORR. We provide very simple MOF free methodology without any post acid treatment or any subsidiary sacrificial metal like Zn. The Mg-N-C catalyst exhibited a half-wave potential of 0.80 V versus the reversible hydrogen electrode, approaching the recently reported Fe-N-C catalyst. Electrochemical calculation further support the Mg-Nx sites as the origin of ORR via efficient 4-electron transfer pathway in basic medium. Importantly, current density is found to decrease less than 2% in diffusion limited current and loss of activity by only 13% at 0.9 V after 10,000 cycles in alkaline medium which far superior to the durability limit set by the US department of energy and overpasses the state-of-the-art Pt/C catalyst. The charge transfer resistance is the crucial parameter influencing on the ORR activity along with (pyridinic N+ pyrrolic N) content and degree of graphitization. This methodology can be applied to design a variety of other alkaline earth metal based M-N-C electrocatalysts and studied for various applications.