|Title||Plasma Engineered Hybrid metal-organic materials as Bi-functional Oxygen Electrocatalyst for renewable energy|
Rechargeable zinc-air batteries have revealed their unlimited potential and economic value for application in electric vehicles and portable electronic devices due to their high theoretical energy density (1084 Wh kg-1), high safety and less-reactive Zn metal. However, the main challenges in high overpotential, low energy efficiency and active sites in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) limiting its widespread commercialization. The state-of-the art noble electrocatalysts (such as Pt, Ru or Ir) have high cost as well as poor stability in charge-discharge process. Among various noble-metal-free electrocatalysts, isolated transitional metal single atom and nitrogen-doped carbon matrix, denoted as M-N4-C, were considered as the most promising materials to substitute noble-metal catalysts with excellent ORR and OER activity owing to the ultra-high atom utilization efficiency and surface active energy. Herein, we demonstrate a novel synthesize route of isolated M-N4/NC (M=Fe, Co, Mn) catalysts via plasma engineering. The atomically dispersed M-N4/NC) catalyst showed superior ORR and OER activity and stability compared to most of other reported electrocatalysts and the commercial Pt/C and Ir/C catalyst in an alkaline medium. In particular, a notable outstanding potential difference ΔE (ΔE = Ej=10 - E1/2) of Co-N4/NC as low as 0.80 V, which outperformed the benchmark Pt-Ir/C catalysts with same catalyst loading (ΔE = 0.85 V). In a home-made Zn-air rechargeable battery, Co-N4/NC as the air electrode catalysts exhibited higher power density, specific capacity and lower overpotential over 100 charge-discharge cycles than that of Pt-Ir/C electrocatalysts. DFT calculation also supported that Co as a central metal atom within N4 matrix has the most balanced ORR and OER mechanism among the studied MN4/NC structure.