Acid-free treatment of fiber-structured biocarbon material enhances flow capacitive deionization performance

Flow capacitive deionization (FCDI) is a new, efficient, and low-energy salt ion removal technology. However, the low connectivity of the active substances within the flow electrode suspension (FES) results in a low electrical conductivity, limiting the large-scale application of FCDI in desalination field. Therefore, we propose a flowable electrode that introduces fiber-structured biocarbon materials (FBCs) as conductive agents in activated carbon (AC), thereby improving the utilization rate of active substances through a conductivity network formed by FBCs. We found that 5 wt% AC with 0.25 wt% CBC (carbonization bacterial cellulose) had higher SAR (1.26–5.92 mM/m2·s) than those of only 5 wt% AC (0.09–2.58 mM/m2·s) under saline water (1.01–35.00 g/L) at 1.8 V. Then, physical and electrochemical characterization results further revealed that a CBC with a high aspect ratio (AR, ∼5000) as conductive agent generated an interconnected conductive network more readily than the introduction of carbonization chitin with a low AR (∼800), untreated CNTs, or spherical carbon black particles, thus increasing the overall conductivity of the FES. Finally, an efficient seawater desalination system was established to lay the foundation for the practical application of FCDI.