Parametric Investigation of Ferri/Ferrocyanide Redox Flow for Performance Optimization of Redox Flow Desalination

Abstract

Redox flow desalination (RFD) presents new opportunities in the water-energy nexus owing to its high energy efficiency and low manufacturing cost. The RFD system introduces an intervening channel for the water stream in a conventional flow battery system, allowing continuous desalination via a sustainable redox reaction on a cathode and an anode at the redox flow channels. However, an operational understanding of the redox flow in RFD is largely unclear; thus, its technological level for practical applications is unexplored. Therefore, this study aimed to investigate the operational features of redox flow in the performance of RFD via parametric investigation. The redox flow was assessed at various mixtures of redox couple and supporting electrolyte (from 200:0 to 0:200 mM ferri/ferrocyanide: NaCl). The optimum RFD performance was observed at a mixture ratio of 40 mM ferri/ferrocyanide and 160 mM NaCl with a salt removal rate of 20.6 mM/g/h, charge efficiency close to unity, and energy consumption of 116.3 kJ/mol. Moreover, the RFD system achieved 99% salt removal and a high salt removal rate of 30.9 mM/g/h at optimized operating parameters including cell voltage, initial feed concentration, the number of electrode stacks, and flow rate. The results not only suggest that the mixture of the redox couple and supporting electrolytes play an important role in effective reactions at the redox flow channels but also provide pivotal insights into operational conditions in the desalination performance.