Multi-electrode scale-up strategy and parametric investigation of redox-flow desalination systems

Abstract

Redox flow desalination (RFD) has emerged as a promising energy-efficient and sustainable electrochemical ion separation process for water desalination. Despite the effectiveness of RFD systems for desalination, prior studies have generally focused on fundamental aspects and lab-scale studies; therefore, the practical feasibility and potential for deployment in industry remain unclear. Here, a strategy for scaling-up RFD systems was developed, and the efficacy of RFD for desalination on a larger scale and its practical feasibility for industrial applications were assessed. A new multielectrode stacking strategy employing a carbon electrode and titanium current collector enabled enhanced charge transfer and improved desalination performance without the need for additional channels. This facile strategy of scaling up the RFD remarkably reduces the size of the system compared with unit cell stacking in the conventional electrochemical system. The larger scale RFD system exhibited a salt removal rate of 852 mmol/m2/h and specific energy consumption of 120 kJ/mol (≅0.1 kWh/m3). Multi-parametric optimization was carried out via interactive data visualization by varying the cell voltage, flow rate, number of carbon electrode stacks, and membrane arrangement. The RFD system achieved an energy consumption of 60–80 kJ/mol and removal rate of 200–300 mmol/m2/h. Overall, the feasibility of RFD for water desalination was confirmed through a rational scale-up strategy, comprehensive understanding of the desalination parameters, and techno-economic analysis. Through continued development and further scale-up investigations, we envision the deployment of RFD systems for energy-efficient desalination on the industrial scale as an alternative to conventional electrochemical desalination processes (i.e., electrodialysis and capacitive deionization).