Membrane-Free Redox Electrochemical Cell Towards Large Scale Energy Storage
Authors: Venkatesan Senthil Velan , Karan Kunal , Larter Stephen R , Thangadurai Venkataraman 
Published: May 2020

Renewable energy sources are forecasted to supply half of the global energy demand in the future. Development of improved and cost-effective energy storage methods are in high demand due to the intermittency and locally distributed nature of renewable energy sources [1]. Redox flow battery (RFB) is a candidate technology for large-scale energy storage that can be coupled with renewable energy to alleviate intermittency problem [2]. A major contributor to the cost (40%) of RFB is the polymer electrolyte membrane, which is supposed to separate the catholyte and the anolyte [3]. Here, we propose membrane-free design wherein the classical anolyte and catholyte compartment, each with a redox auxiliary electrode pair, are connected by a metal wire. This design relieves the restriction of finding a common electrolyte for the anode and cathode chamber and eliminates the cross-over of undesirable ions between the two chambers. Thus, the new design offers the flexibility of using a wide variety of redox electrolytes (alkaline/acidic or aqueous/non-aqueous) in anode and cathode chambers independently [4]. For example, two compartment redox cell with a pair of auxiliary electrode allows the use of aqueous (acidic/alkaline) or nonaqueous (acidic/alkaline) electrolytes in anode and cathode chambers independent of one another, with electron conducting material connecting the auxiliary electrodes in both chambers during charging and discharging reactions as shown in Figure 1. When oxidation occurs at the anode, corresponding auxiliary electrode udergoes reduction and hence an oxidized materials must be supplied here. Whereas, reduction occurs at the cathode and corresponding auxiliary electrode udergoes oxidation and hence a reduced materials must be supplied to enable a spontaenous charging and discharging of the redox electrolyte. The novel design helps couple spatially separated oxidation and reduction processes. Since, there is no membrane and mass transport across the chambers, the cost, performance, and degradation issues related to membrane are avoided. Alkaline and acidic electrolytes can be used indepenedent of the content in the other chamber. When the solubility of one type of redox electrolyte is limited or zero in aqueous solvent, that particular redox electrolyte alone can be dissolved in a different media/solvent and retain the counter electrolyte in aqueous based solvent [5].

Acknowledgements

This research was undertaken thanks in part to funding from the University of Calgary and the Canada First Research Excellence Fund.

References

1. Larcher, D. Tarascon, Jean-Marie. Nat. Chem. 7 (2015)19-29.
2. Grigorii Soloveichik, Nature. 505 (2014) 163-165.
3. Puiki Leung, T. Martin, Akeel A. Shah, Mohd Rusllim Mohamed, Marc A. Anderson, Jesus Palma, J. Power Sources. 341 (2017) 36-45.
4. Senthil Velan Venkatesan, Venkataraman Thangadurai, Steve Larter, Kunal Karan, Jagos Radovic, US provisional patent application 62/887,464 filed August 15, 2019.
5. Senthil Velan Venkatesan, Kunal Karan, Steve Larter, Venkataraman Thangadurai, Sustainable Energy & Fuels.
(2019) doi:1039/C9SE00734B.

Figure 1