Zinc–Cerium and Related Cerium‐Based Flow Batteries: Progress and Challenges

The Zn–Ce flow battery (FB) has drawn considerable attention due to its ability to achieve open-circuit voltages of up to 2.5 V, which surpasses any other aqueous, hybrid FB or Zn-based FB chemistry. This Zn–Ce FB was introduced in the early 2000s, building upon the proven industrial electrolysis of cerium ions for mediated organic electrosynthesis and specialist oxidative cleaning together with the classical use of zinc in discharging battery anodes. The half-cell reactions involve the Ce 3+ /Ce 4+ and Zn/Zn 2+ redox couples at the positive and negative electrodes, respectively. Electrode kinetics, electrode materials, and electrolyte compositions, including mixed acids, have been studied. Lately, hydrodynamic simulations of the positive half-cell and life-cycle analysis have been performed, in addition to more extended charge/discharge cycling. Scale-up tests have involved 0.25 m 2 membrane-divided cells with composite carbon high-density-polyethylene bipolar electrodes coated with Ti and Pt by physical vapor deposition and a discharge power density of 2 kW m −2 . In view of the moderate cost of cerium, variants have been developed to complement the positive electrode reaction, resulting in V–Ce and Ti–Ce FBs, H 2 –Ce half-fuel cells, and, more recently, novel chemistries based on inorganic and organic Ce complexes. Recommended R & D studies to further research knowledge and aid industrial development are highlighted.