Zn glutarate protective layers in situ form on Zn anodes for Zn redox flow batteries

Abstract

We developed in situ formation of protective layers using glutaric acid (GA) and Zn2+ in the electrolyte solution and revealed a pH-sensitive growth mechanism. GA additives were deprotonated during the initial hydrogen evolution reaction (HER) and integrated via Zn2+ coordination, forming a laminar-shaped Zn glutarate layer with similar to 50 nm thickness. In addition, the dissociated protons remained in the solution pH constantly. In this condition, the Zn glutarate layer prevented HER and Zn hydroxide sulfate hydrate (ZHS) precipitation. GA-containing 1 M ZnSO4 solution at pH 5.0 was subjected to over 4000 h cycling at 0.5 mA cm(-2) in Zn|Zn cells and demonstrated long-term cycled Zn-iodide redox flow batteries. In comparison, GA-free cells delivered far lower cyclabilities because the growing ZHS induced dendritic Zn deposition. This study demonstrated a novel strategy to form thin Zn-organic protective layers in a simple, cheap, and effective manner.