Polysulphide Air Redox Flow Battery - a Novel Solution for Grid Scale Energy Storage

The widespread deployment of flow batteries, an important part of energy storage technologies, has been largely restricted by its high cost. A novel, recently patented redox flow system utilising polysulphide redox and oxygen reduction/evolution reactions offers a cost effective solution for electricity storage and delivery.

The schematic operation of polysulphide-air flow battery is illustrated in the Figure below. The polysulphide anolyte is pumped through the porous media at the anode compartment when the reversible electrochemical redox reaction of soluble polysulphide/sulphur occurring. Concurrently the oxygen reduction/evolution occurs at catalytically active gas diffusion media at the cathode compartment. Experimental testing of polysulphide-air system was carried out in 5 cm² active area single cell setup connected to peristaltic and air pumps. The stable open circuit voltage of 0.68 V was achieved in 0.5 Na₂S/ 0.5 M S/ x 1M NaOH solution. This OCV was slightly lower than the theoretical value of 0.85V likely due to crossover of anolyte species and bad contact of circut. A maximum power density of 2.1 mW/cm² was achieved during the discharge. To decouple anode and cathode processes half-cell measurements including electrochemical impedance spectroscopy were performed. The collected data clearly indicate that the major losses happened on polysulphide side. Increased flow rate of polysulphide anolyte just slightly improved the performance. This work will present novel data with improved catalytic activity of polysulphide side and increased performance of the polysulphide-air system.