Nanohybrid structured RuO2/Mn2O3/CNF as a catalyst for Na-O2 batteries.

A 3D RuO2/Mn2O3/carbon nanofiber (CNF) composite has been prepared in this study by a facile two step microwave synthesis, as a bi-functional electrocatalyst towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). RuO2 nanoparticles with the mean size of 1.57 nm are uniformly distributed on Mn2O3 nano-rods grown on electrospun CNFs. The electrocatalytic activity of the composites are investigated towards ORR/OER under alkaline condition. The ternary RuO2/Mn2O3/CNF composite showed superior ORR activity in terms of onset potential (0.95 V versus RHE) and Tafel slope (121 mV dec-1) compared to its RuO2/CNF and Mn2O3/CNF counterparts. In the case of OER, the RuO2/Mn2O3/CNF exhibited 0.34 V over-potential value measured at 10 mA cm-2 and 52 mV dec-1 Tafel slope which are lower than those of the other synthesized samples and as compared to state of the art RuO2 and IrO x type materials. RuO2/Mn2O3/CNF also exhibited higher specific capacity (9352 mAh [Formula: see text]) than CNF (1395 mAh [Formula: see text]), Mn2O3/CNF (3108 mAh [Formula: see text]) and RuO2/CNF (4859 mAh g carbon -1) as the cathode material in Na-O2 battery, which indicates the validity of the results in non-aqueous medium. Taking the benefit of RuO2 and Mn2O3 synergistic effect, the decomposition of inevitable side products at the end of charge occurs at 3.838 V versus Na/Na+ by using RuO2/Mn2O3/CNF, which is 388 mV more cathodic compared with CNF.