Impact of Acetate Additive on PbO₂ Plating and Oxygen Evolution in Soluble Lead Flow Batteries

Abstract

Soluble lead flow batteries (SLFBs), a potential form of large-scale energy storage, are currently facing the challenge of short cycle life. We previously demonstrated that by adding sodium acetate (NaOAc) in the electrolyte, the life span of SLFBs can be significantly extended. Here, we aim to elucidate the effect of acetate additive on SLFBs. We find that the mechanical strength of the PbO2 layer plated by acetate-assisted electrolyte is materially enhanced. Through electron back-scattering diffraction, certain preferred orientations of deposited PbO2 are observed when plated without acetate additive, while random orientations are better preserved when plated with acetate additive. Via Brunauer–Emmett–Teller measurements, we find that porosity and surface area are both comparatively smaller in the acetate-assisted PbO2 deposits, while the rate of oxygen evolution reaction (OER) is shown to be drastically reduced on PbO2 plated with NaOAc-assisted electrolyte. We further propose that the OER pathway is suppressed by the additive due to acetate-ion adsorption at superficial PbO2 sites, and in turn facilitates PbO2 plating. These further discoveries are of critical value for further extending cycle life and enabling SLFB technology.