An Acid-Base Electrochemical Flow Battery as energy storage system

Abstract

In this paper, we present a new Acid-Base Electrochemical Flow Battery (ABEFB). This system is composed of acidic and alkaline solutions, both with a high supporting electrolyte concentration. These solutions are separated by a proton exchange membrane, using hydrogen as both a reactant and a product. Under this configuration, neutralization energy is used as electromotive force. Thus, in the charging process, hydrogen is oxidized to form hydronium ions (hydrogen oxidation reaction –HOR-) (positive electrode) that acidifies positive electrolyte or posilyte, while hydrogen is formed from water (hydrogen evolution reaction –HER-) (negative electrode) that basifies negative electrolyte or negalyte. On the other hand, during the discharging process, both electrolytes are neutralized through hydrogen oxidation and hydrogen evolution reactions. A platinised titanium electrode is chosen for HER and a platinum-catalysed gas diffusion electrode is used for HOR. This proof of concept has been verified for several charge capacities obtaining a maximum power density of 20 mW cm−2 at 49 mA cm−2. In this sense, faradaic efficiency close to 95% and energy efficiency of 55% are also obtained. Finally, the reuse of produced hydrogen is an interesting aspect to be considered.