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

Abstract

• Developing of Zn powder and dust electrode for aqueous Zn/MnO 2 battery. • Zn powder with grain sizes >500 µm attenuate its corrosion and dissolution in NH 4 Cl solution. • Assembling of Zn powder or dust (anode) with electrolytic (EMD) or nanostructured (NMD) MnO 2 (cathode) in Zn/MnO 2 cell. • Zn powder (>500 µm)/NMD cell yields a highest output voltage of 1.646 V. • Specific energy (109.722 mWh/g) and the lowest voltage drop of 0.7% after 2 h of discharge. This work gives an insight into how zinc (Zn) anode in the Zn/MnO 2 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 NH 4 Cl 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(NH 3 ) 2 Cl 2 molecules. These electrodes, with two distinct shapes, were used as anodes in assembled Zn/MnO 2 batteries with two types of MnO 2 cathode namely nanostructured manganese dioxide (NMD) and electrolytic manganese dioxide (EMD). Discharge tests showed high performance for Zn/MnO 2 cell based on Zn powder (>500 µm) as anode and NMD as a cathode in NH 4 Cl 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/MnO 2 can be used for low cost and high-performance battery with a specific structure and shape of both anode and cathode materials.