Zinc–cerium battery

Zinc–cerium batteries are a type of redox flow battery first developed by Plurion Inc. (UK) during the 2000s. In this rechargeable battery, both negative zinc and positive cerium electrolytes are circulated though an electrochemical flow reactor during the operation and stored in two separated reservoirs. Negative and positive electrolyte compartments in the electrochemical reactor are separated by a cation-exchange membrane, usually Nafion (DuPont). The Ce(III)/Ce(IV) and Zn(II)/Zn redox reactions take place at the positive and negative electrodes, respectively. Since zinc is electroplated during charge at the negative electrode this system is classified as a hybrid flow battery. Unlike in zinc–bromine and zinc–chlorine redox flow batteries, no condensation device is needed to dissolve halogen gases. The reagents used in the zinc-cerium system are considerably less expensive than those used in the vanadium flow battery.

Due to the high standard electrode potentials of both zinc and cerium redox reactions in aqueous media, the open-circuit cell voltage is as high as 2.43 V. Among the other proposed rechargeable aqueous flow battery systems, this system has the largest cell voltage and its power density per electrode area is second only to H2-Br2 flow battery.Methanesulfonic acid is used as supporting electrolyte, as it allows high concentrations of both zinc and cerium; the solubility of the corresponding methanesulfonates is 2.1 M for Zn, 2.4 M for Ce(III) and up to 1.0 M for Ce(IV). Methanesulfonic acid is particularly well suited for industrial electrochemical applications and is considered to be a green alternative to other support electrolytes.

The Zn-Ce flow battery is still in early stages of development. The main technological challenge is the control of the inefficiency and self discharge (Zn corrosion via hydrogen evolution) at the negative electrode. In commercial terms, the need for expensive Pt-Ti electrodes increases the capital cost of the system in comparison to other RFBs.

At the negative electrode (anode), zinc is electroplated and stripped on the carbon polymer electrodes during charge and discharge, respectively.

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