Rare-metal-free Zn–air batteries with ultrahigh voltage and high power density achieved by iron azaphthalocyanine unimolecular layer (AZUL) electrocatalysts and acid/alkaline tandem aqueous electrolyte cells

Abstract

Zn–air batteries have only been used in limited applications, such as hearing aid batteries, due to their low power density and standard voltage of around 1.4 V. Therefore, to use Zn–air batteries as a drive power source in cutting-edge devices such as drones, it is essential to improve the drive voltage and output power density. Here, we propose Zn–air batteries with a high potential (∼2.25 V) and high power density (∼318 mW/cm2) by using the newly designed iron azaphthalocyanine unimolecular layer (AZUL) electrocatalyst and a tandem Zn–air battery cell. The AZUL electrocatalyst in this new type of cell had a high electrochemical stability and high oxygen reduction reaction performance in the ultralow pH region, in which Pt and other metallic and inorganic electrocatalysts cannot be used. Furthermore, the tandem-electrolyte cells had a cell voltage of over 1.0 V at a high discharge current density of 200 mA/cm2, and the output power density was 1139 mWh/g(Zn) at 100 mA/cm2 discharge.