Printed air cathode for flexible and high energy density zinc-air battery
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Printed air cathode for flexible and high energy density zinc-air battery Soorathep Kheawhom and Sira Suren Computational Process Engineering, Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok 10330, Thailand ABSTRACT Flexible zinc-air batteries were fabricated using an inexpensive screen-printing technique. The anode and cathode current collectors were printed using commercial nano-silver conductive ink on a polyethylene terephthalate (PET) substrate and a polypropylene (PP) membrane, respectively. Air cathodes made of blended carbon black with inexpensive metal oxides including manganese oxide (MnO2) and cerium oxide (CeO2), were studied. The presence of the metal oxides in the air cathodes enhanced the oxygen reduction reaction which is the most important cathodic reaction in zinc-air batteries. The battery with 20 %wt CeO2 showed the highest performance and provided an open-circuit voltage of 1.6 V and 5 – 240 mA.cm-2 ohmic loss zone. The discharge potential of this battery at the current density of 5 mA.cm-2 was nearly 0.25 V higher than that of the battery without metal oxides. Finally, the battery was tested for its flexibility by bending it so that its length decreased from 2.5 to 1 cm. The results showed that the bending did not affect characteristics on potential voltage and discharging time of the batteries fabricated. INTRODUCTION Fabrication of electronic devices and batteries using printing techniques is particularly interesting due to their simplicity, high-throughput and environmental friendliness1-4. Moreover, these techniques enable the fabrication of devices that are large in area, low cost, wearable and flexible. Various types of batteries have been successfully fabricated by printing techniques e.g. zinc-manganese oxide batteries5, lithium ion batteries6 and zinc-air batteries7. Zinc-air batteries show great promise for future energy applications and recently attract tremendous attention8. These batteries use relatively low cost, low toxicity and environmentally friendly raw materials while providing high specific energy density. Moreover, these batteries use an aqueous solvent and zinc which is relatively safe and stable. A zinc-air battery cell is basically composed of current collectors for both anode and cathode, an anode electrode containing zinc metal, a cathode electrode with gas diffusion and catalyst layers, and a separator soaked with electrolyte. The performance of an air cathode has a decisive impact on the performance of a zinc-air battery because the sluggish oxygen reduction reaction (ORR) kinetics increase overpotential and decrease power density as well as performance of the battery. Various works have been carried out for developing electro-catalysts in order to reduce overpotential and enhance the performance of the batteries9. The most frequently studied ORR electro-catalysts can be classified into three categories including precious metals10, metal oxides11,12 or carbonaceous materials13.
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