Zinc–cerium battery

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Zinc–cerium batteries are a kind of redox flow battery where zinc metal is used at the negative side and cerium species at the positive side. The two electrolytes are stored in separate tanks and pumped through an electrochemical cell, with a cation-exchange membrane (often Nafion) separating the positive and negative sides. On the negative side, zinc undergoes Zn(II)/Zn redox reactions; on the positive side, Ce(III)/Ce(IV) redox reactions occur. Because zinc is plated at the negative electrode during charging, this is considered a hybrid flow battery.

The system uses relatively inexpensive materials compared with vanadium-based flow batteries and can deliver a high open-circuit voltage, around 2.4 volts. It does not produce halogen gases as some other zinc-based flow systems do, which simplifies the design. Methanesulfonic acid serves as the supporting electrolyte, enabling high solubility for both zinc and cerium species and is regarded as a greener alternative to many other electrolytes.

The zinc–cerium flow battery was first proposed in 2004 by Clarke and colleagues for Plurion Inc. (UK). The company faced financial troubles later, but the concept and its performance were explored by researchers in the UK and elsewhere. Early lab tests reported coulombic efficiencies around 92% and voltage efficiencies near 68% during cycling at modest current densities. A membraneless, undivided version with low acid concentration showed about 2.1 V discharge voltage and roughly 75% energy efficiency. A large (>2 kW) testing facility in Scotland demonstrated the technology at a bigger scale.

Key challenges remain. The negative electrode can suffer from self-discharge and zinc corrosion with hydrogen evolution, which reduces efficiency. Platinum–titanium-based electrodes, while effective, raise capital costs. At high cell voltages, side reactions producing hydrogen or oxygen could occur, especially during charging. Positive electrodes have been studied with titanium-based materials or carbon felt, and researchers have tested various alternatives, including coated and catalytic electrodes, conductive carbons, and graphene-related materials to improve kinetics.

Ongoing research focuses on electrolyte composition (including mixed acids to speed cerium reactions), electrode materials, and cell design to reduce losses and self-discharge. With continued development, the zinc–cerium system could offer a competitive option for large-scale energy storage and related industrial applications.