The influence of a chloride-based supporting electrolyte on electrodeposited zinc in zinc/bromine flow batteries

Abstract

A combination of analytical techniques and molecular modelling methods was used to study the influence of chloride-based supporting electrolytes on zinc electrodeposit surfaces in the zinc half-cell of zinc/bromine flow batteries. Scanning electron microscopy and X-ray diffraction analysis of zinc electrodeposits obtained during charging show that: (a) the primary preferred orientation is planar, and (b) increasing the duration of exposure to the Cl-containing electrolyte influences crystallinity and changes the preferred secondary orientations. Analysis using periodic density functional methods indicates that the binding energy of Cl to the Zn(001) surface depends more strongly on surface coverage than on binding site location. Solvation increases the stability of Cl binding to the surface. The binding energies of Cl with and without water solvation are between 288 and 327 kJ mol−1 and 249–288 kJ mol−1, respectively, for coverages between 0.11 and 0.33 ML. The binding of Cl leads to Zn surface buckling and decreases surface uniformity. Binding at 0.33 ML and above results in surface instabilities, leading to the formation of surface cavities due to significant vertical displacement of surface Zn sites.