Pen-drawn air cathode featuring graphite felt substrate modified with MnO2-decorated graphene flakes and PEDOT network for rechargeable zinc–air battery

Abstract

Zinc–air batteries (ZABs) have drawn attention recently as alternatives to conventional Li-ion batteries because of their high energy density, abundance in the earth’s crust, and relatively low production cost. Although ZABs are incredibly stable under normal conditions unlike popular Li-based energy storage devices, many challenging issues remain. Requirements such as rechargeability, low-cost fabrication, and mass production of an effective bifunctional catalyst restrict the use of commercial ZABs to a few small electronic gadgets. In this study, we introduce a functionalized pen-drawable ink composed of amorphous MnO2 with a large specific area, graphene sheet (GS) flakes, and poly(3,4-ethylenedioxythiophene) (PEDOT). The MnO2-decorated GS is successfully immobilized on graphite felt (GF) using the PEDOT network. The pen-drawn MnO2@GS/PEDOT/GF substrate is further used as a bifunctional air cathode. Power density of the air cell is 37.8 mW·cm−2 at 55 mA·cm−2. The potential difference between the half-wave potential of the oxygen reduction reaction and the operational potential of the oxygen evolution reaction is 0.74 V; this value is comparable to that of traditional noble metal catalysts, and is obtained at a current density of 10 mA·cm−2 with the pen-drawn cathode in a two-electrode system containing a conventional 6 M KOH electrolyte.