Zinc Electrodeposition in the Presence of an Aqueous Electrolyte Containing 1-Ethylpyridinium Bromide: Unexpected Oddities

Abstract

The reversible electrodeposition of zinc was investigated in an aqueous electrolyte containing zinc bromide (50 mM) and 1-ethylpyridinium bromide ([C2Py]Br, 50 mM) by cyclic voltammetry, chronoamperometry, and scanning electron microscopy. Unusual voltammetric behaviour for the Zn/ZnII redox couple was observed in the presence of [C2Py]Br. Passivation of the redox couple was observed after a single deposition–stripping cycle at switching potentials more negative than −1.25 V versus Ag/AgCl. This unusual behaviour was attributed to the reduction of 1-ethylpyridinium cations to pyridyl radicals and their follow-up reactions, which influenced the zinc electrochemistry. This behaviour was further seen to modify the nucleation process of electrodeposition, which altered the morphology of zinc electrodeposits.

The Influence of Pyridinium-Based Additives on Zinc Electrodeposition in Aqueous Solution

“…This indicates no additional zinc was deposited on the reverse scan, and subsequently a lower current is observed for the stripping process, similar to previously reported results. 28 Extending the switching potential to −1.50 V (Figure 4c), the zinc deposition process on the first cycle was similar to that observed in the absence of N-ethylpyridinium bromide (Figure 4a). Notably, an additional irreversible reduction with a peak potential of −1.42 V and an additional irreversible oxidation process at a potential range between −0.45 and −0.20 V, were observed.…”

“…33 The complex is derived from the dimer molecule, and likely also has a low solubility in aqueous solutions, potentially inhibiting the electrode surface, and is reduced at less positive potentials than the N-ethylpyridinium cation reduction. Based on our and previous results, 21,22,25,28 the mechanism for N-ethylpyridinium cation reduction and the related dimer oxidation in aqueous media is proposed in Scheme 1.…”

Zinc–Bromine Batteries: Challenges, Prospective Solutions, and Future

“…[111] Similar results were also reported by Easton et al using 1-ethylpyridium bromide as an additive. [112] Modifying electrode surfaces can tune electrode/electrolyte interfaces. A common approach is to add a surface protective layer between electrodes and electrolytes to prevent undesirable side reactions and regulate ionic distribution in many other types of batteries.…”