Bimetallic Mn-Co Oxide Nanoparticles Anchored on Carbon Nanofibers Wrapped in Nitrogen-Doped Carbon for Application in Zn-Air Batteries and Supercapacitors

The exploration and rational design of cost-effective, highly active, and durable catalysts for oxygen electrochemical reaction is crucial to actualize the prospective technologies such as metal-air batteries and fuel cells. Herein manganese cobalt oxide nanoparticles anchored on carbon nanofibers and wrapped in a nitrogen-doped carbon shell (MCO/CNFs@NC) is successfully prepared. Benefiting from the synergistic effect between the core nanoparticles and nitrogen-doped carbon shell, MCO/CNFs@NC catalyst exhibits oxygen reduction reaction (ORR) activity with comparable onset potential (1.00 V vs RHE) and half-wave potential (0.76 V vs RHE) which is only about 40 mV lower than that of the state of art Pt/C catalyst. Furthermore, the MCO/CNFs@NC catalyst exceeds the Pt/C catalyst by a great margin in terms of stability in alkaline media. Additionally, MCO/CNFs@NC catalyst is strongly tolerant to methanol crossover, promising its applicability as cathode catalyst in alcohol fuel cells. Moreover, MCO/CNFs@NC catalyst exhibits the oxygen evolution reaction (OER) activity with low overpotential of 0.41 V at the current density of 10 mA cm(-2) and ORR/OER potential gap (Delta E) as low as 0.88 V, suggesting its strong bifunctionality. The Zn-air battery based on MCO/CNFs@NC catalyst is found to deliver a specific capacity of 695 mA h g(Zn)(-1) and an energy density of 778 W h kg(Zn)(-1) at a current density of 20 mA cm(-2). The mechanically rechargeable Zn-air battery based on MCO/CNFs@NC catalyst is also found to function continually by only reloading the consumed Zn anode and electrolyte. Furthermore, the electrically rechargeable battery based on MCO/CNFs@NC catalyst is found to function for more than 220 cycles with negligible loss of voltaic efficiency. Moreover, MCO/CNFs@NC is found to display a supercapacitive nature with a good discharge capacity of 478 F g(-1) at a discharge current density of 1 A g(-1).