A Hexagonal Honeycomb-Shaped Flow Channel for High-Efficient Desalination and Flowability in Flow-Electrode Capacitive Deionization

Abstract

Flow-electrode capacitive deionization (FCDI) is a prospective alternative for large-scale desalination applications due to the efficient flowability of the electrode slurry. However, flow channel blockages and slurry leakage in conventional FCDI cells have severely limited the salt removal and stable operation. Based on the synergistic effects of diverting and guiding flow, a hexagonal honeycomb-shaped flow channel (HH-channel) was innovatively applied to the FCDI system to optimize the hydrodynamic behavior of the slurry, which greatly reduced the hydraulic pressure and enhanced the desalination performance. What is more, we first introduced a Two-Phase Transport Mixture model and combined it with computational fluid dynamics (CFD) simulations to further confirm that more uniform distribution of carbon particles in the HH-channel facilitates the construction of a charge percolation network and charge transfer compared to a serpentine single-track flow channel (SS-channel) and rectangular-cavity flow channel (RC-channel). After a long-term operation test (1800 min, U = 1.6 V), the FCDI system with the HH-channel exhibited superior desalination stability, with a faster average salt removal rate (ASRR) of 2.05 μmol cm–2 min–1 and salt removal efficiency (SR) of 64.89% and charge efficiency (CE) of 96.06%. In summary, our work developed a facile strategy for optimizing the flow channel geometry to improve slurry flowability and obtain an efficient and steady desalination application.