(47a) Role of Hydrogen Evolution Reaction during Zinc Electrodeposition from Flowing Alkaline Zincate Solutions

Zinc electrodes in alkaline solutions have been tested over time in a combination with various redox couples in primary and secondary cells. A very promising use of a zinc seems to be in flow batteries, where a flow of an electrolyte can solve a dendritic growth of the zinc metal, which is a main obstacle that prevents a successful development of the secondary batteries based on the alkaline zinc chemistry. Besides that, an attention has to be paid to a presence of hydrogen evolution reaction, which is known as a parasitic reaction during the zinc electrodeposition from an alkaline zincate solutions. The hydrogen evolution reaction is responsible for current efficiency losses during the electrolysis, but rising hydrogen bubbles also cause an extra convection within a diffusion layer, which leads to an enhanced mass transport of zincate ions to an electrode surface.

This work is aimed to determine an influence of the hydrogen evolution reaction on the zinc electrodeposition from the flowing alkaline zincate solutions. The study consisted of experimental electrodepositions of the zinc metal in an electrolyzer with the convective flow of the electrolyte and a subsequent data evaluation by mathematical models. The results show a complex role of the hydrogen evolution reaction during the zinc electrodeposition from the flowing alkaline zincate solutions, which complicates usage of a limiting current density as a morphology indicator of the zinc electrodeposition.