An Electrically Rechargeable Zinc/Air Cell with an Aqueous Choline Acetate Electrolyte

Abstract

<jats:p>Due to the feasibility of an electrically rechargeable zinc/air cell made of a zinc foil as active material, an aqueous choline acetate (ChAcO) mixture as an electrolyte and a spinel MnCo2O4 (MCO) and NiCo2O4 (NCO) as a bi-functional oxygen catalyst was investigated in this work. The 30 wt.% water-containing aqueous ChAcO solution showed high contact angles close to those of KOH favoring triple-phase boundary formation in the gas diffusion electrode. Conductivity and pH value of 30 wt.% H2O/ChAcO amounted to 5.9 mS cm−1 and 10.8, respectively. Best results in terms of reversible capacity and longevity of zinc/air cell were yielded during 100 h charge/discharge with the MnCo2O4 (MCO) air electrode polarization procedure at 100 µA cm−2 (2.8 mA g−1zinc). The corresponding reversible capacity amounted to 25.4 mAh (28% depth of discharge (DOD)) and the energy efficiency ranged from 29–54% during the first and seventh cycle within a 1500 h polarization period. Maximum active material utilization of zinc foil at 100 µA cm−2 was determined to 38.1 mAh (42% DOD) whereas a further charging step was not possible due to irreversible passivation of the zinc foil surface. A special side-by-side optical cell was used to identify reaction products of the zinc/air system during a single discharge step in aqueous ChAcO that were identified as Zn(OH)2 and ZnO by Raman analysis while no carbonate was detected.</jats:p>

Solvation and Ion‐Pairing Effects of Choline Acetate Electrolyte in Protic and Aprotic Solvents Studied by NMR Titrations

“…The electrochemical performance of choline‐based electrolytes has been recently assessed by Liu, Sakthivel et al . in Zn‐air cells [50–52] . It was found that aqueous choline acetate showed good compatibility with the selected electrode/catalyst and reduction of dendrite formation.…”

“…The electrochemical performance of choline-based electrolytes has been recently assessed by Liu, Sakthivel et al in Zn-air cells. [50][51][52] It was found that aqueous choline acetate showed good compatibility with the selected electrode/catalyst and reduction of dendrite formation. It has previously been shown that choline-based ILs exhibit a solvent-shared ion pair (SIP) configuration at high salt concentrations in the presence of H 2 O.…”