Feasibility of All-Copper Hybrid Redox Flow Battery for Large Scale Energy Storage

Copper redox flow batteries have been newly studied and offer many advantages over other redox flow battery chemistries [1-3].  There is little hydrogen evolution, no dendrite formation has been observed, and it is an all copper system which indicates no crossover contamination. Preliminary analysis indicates an open circuit voltage of 0.81 volts as shown in Figure 1. Although the all copper redox flow battery has a relatively low open circuit voltage, the all copper redox flow batter provides a platform for a simple and cost-effective flow battery system. In this research, the all copper redox flow battery in bromide electrolyte has been studied in a prototype 6.45 cm²electrode single cell. Charge-discharge cycling achieved coulombic efficiencies over 85% and voltaic efficiencies greater than 75%. However, capacity fade was observed and preliminary results suggest this is due to metallic copper loss at the negative electrode. This is most likely due to non-ideal plating morphologies which have been studied independently as a function of current density and electrolyte composition. We will report on our cell testing and single electrode experiments for this promising flow battery chemistry.

Figure 1: Cyclic voltammogram of 0.5M Cu¹⁺  in 4M NaBr, 1M HBr, and 0.5M Br^-. This is the last of 5 cycles at a scan rate of 10 mV/s, on a graphite working electrode, and using a silver-silver chloride reference electrode. The Cu^0/1+ and Cu^1+/2+ standard potentials are approximately -0.26 and 0.55 volts, respectively indicating the all copper redox flow battery has an open circuit potential of 0.81 volts.

References:

[1] D. Lloyd, T. Vainikka, K. Kontturi, Electrochimica Acta, 100 (2013) 18-23.

[2] L. Sanz, D. Lloyd, E. Magdalena, J. Palma, K. Kontturi, Journal of Power Sources, 268 (2014) 121-128.

[3] L. Sanz, D. Lloyd, E. Magdalena, J. Palma, M. Anderson, K. Kontturi, Journal of Power Sources, 278 (2015) 175-182.