The effect of zinc shape on its corrosion mitigation as an anode in aqueous Zn/MnO2 battery

Abstract This work gives an insight into how zinc (Zn) anode in the Zn/MnO2 batteries is corroded depending on its shape (in the form of powder or dust), and how such shape can play a role to attenuate the Zn corrosion and dissolution during an electrochemical process. Indeed, the corrosion of Zn anodes in powder and dust shape was investigated in ammonium chloride aqueous NH4Cl solution using open circuit potential (OCP) plot, linear polarization (LP), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) methods. The electrodes were also observed by scanning electron microscopy (SEM) and analyzed using X-ray diffraction (XRD). The results show that the corrosion rate significantly depends on Zn grain size and surface area. In addition, the SEM observations showed clearly some corrosion features on the surface of Zn grains. Furthermore, the XRD analysis confirms the formation of a corrosion layer constituted of ZnO and adsorbed Zn(NH3)2Cl2 molecules. These electrodes, with two distinct shapes, were used as anodes in assembled Zn/MnO2 batteries with two types of MnO2 cathode namely nanostructured manganese dioxide (NMD) and electrolytic manganese dioxide (EMD). Discharge tests showed high performance for Zn/MnO2 cell based on Zn powder (>500 µm) as anode and NMD as a cathode in NH4Cl electrolyte, with an output voltage of 1.65 V and specific energy of 109.72 mWh/g after 2 h under 1 mA. Moreover, this cell is the most stable with a voltage drop as low as 0.7% after 2 h of continuous discharge. Such results demonstrate that the assembled Zn/MnO2 can be used for low cost and high-performance battery with a specific structure and shape of both anode and cathode materials.