Iron, copper, and nickel behavior in buffered, neutral aluminum chloride: 1-methyl-3-ethylimidazolium chloride molten salt

Iron, copper, and nickel electrodes were examined as possible metal/metal(II) chloride cathodes for the room temperature sodium/metal chloride battery in a molten salt composed of sodium chloride (NaCl), aluminum chloride (AlCl3), and 1-methyl-3-ethylimidazolium chloride (MEIC). The iron electrode was investigated in basic, neutral-like, and acidic MEIC:AlCl3 melts. The solubility and the kinetics of the reduction of Fe(II) was a function of acidity. In the basic melt, the FeCl2 was soluble; however, its reduction was not observed due to slow kinetics. In the neutral-like and acidic melts, the quasi-reversible reduction of Fe(II) to Fe(0) was observed. The redox potential of copper was approximately 1 V more positive of iron; however, the oxidized copper was soluble in the neutral-like melt, making it unacceptable without a separator. The oxidized and reduced forms of nickel were insoluble and the redox potential was 2.5 V positive of Na/Na+. The nickel electrode supported a charge density of 3.5 mC/cm(2) at room temperature, suggesting that a high-surface-area electrode would be needed in a practical device.