Suspended hydrophilic carbon anodes to enable fully flowable cerium–metal hybrid flow batteries

Abstract

Hybrid redox flow batteries (RFBs) are a special type of RFBs that involve depositing reactions on negative electrodes. The available volume in negative electrodes for cell stacks limits the totally energy-storing capability of these batteries. This paper introduces the first fully flowable Ce–metal flow battery operated with a semisolid, flowable anolyte. Using the semisolid fuel cell concept, we incorporate the sustainable and deposit-abundant features of non-Li-based batteries into the structure of RFBs to develop a fully flowable RFB system. Solid suspension electrodes of hydrophilic carbon particles deposited by earth-abundant metals with redox activity are investigated as alternatives to the redox-active molecules employed in typical RFBs to decouple the power delivery capability from the energy storage capacity in fully flowable RFBs. While being charged, earth-abundant redox-active metal (Cu, Pb or Zn) is electrodeposited on the carbon particle suspension, which is dissolved in the sequent discharging process. On the basis of the proposed contact-charge-transfer mechanism, the electrical contact to the solid suspension electrode is fed by the redox-inert hydrophobic current collector that restrains direct metal deposition on their surfaces due to the hydrophobicity.