Reduced Graphene Oxide decorated with Manganese Cobalt Oxide as Multifunctional Material for Mechanically Rechargeable and Hybrid Zinc-Air Batteries

Spinel MnCo2O4 nanoparticles on nitrogen-doped reduced graphene oxide (MnCo2O4/NGr) are synthesized for advanced zinc-air batteries with remarkable cyclic efficiency and stability. The synthesized MnCo2O4/NGr exhibits good oxygen-reduction reaction (ORR) activity with half-wave potential E-1/2 of 0.85 V (vs reversible hydrogen electrode (RHE)), comparable to commercial Pt/C with E-1/2 of 0.88 V (vs RHE) along with superior oxygen electrode activity Delta E = 0.91 V for the ORR/OER (oxygen-evolution reaction) in alkaline media. Durability tests confirm that MnCo2O4/NGr is more stable than Pt/C in alkaline environment. MnCo2O4/NGr functions with stable discharge profile of 1.2 V at 20 mA cm(-2), large discharge capacity of 707 mAh g(Zn)(-1) at 40 mA cm(-2) and a high energy density of 813 Wh kg(Zn)(-1) in a mechanically rechargeable zinc-air battery. The electrically rechargeable MnCo2O4/NGr zinc-air battery displays hybrid behavior with both Faradaic and oxygen redox charge-discharge characteristics, operating at higher voltage and providing higher power density and excellent cyclic efficiency of 86% for over 100 cycles compared to Pt/C with efficiency of around 60%. Moreover, hybrid zinc-air battery operates with a stable and energy efficient profile at different current densities.