Great truths are always simple: Preoxidation-tuned cellulose-derived carbon fibers achieving ultrahigh areal desalination capacity in flow-through capacitive deionization

Constructing thick electrodes with both high strength and porous characteristics is challenging but critical to improve the desalination performance of flow-through capacitive deionization (FTCDI). Different from the most reported electrodes composed of carbon nanomaterials, micron-sized carbon fibers are more advantageous due to the innate excellent mechanical stability and macroscopic porous fibrous structure. Herein, we reported the preoxidation-tuned cellulose-derived carbon fibers (POCF) with improved specific surface area, pore volume, hydrophilicity, and carbon defect degree by precisely-controlled preoxidation process, resulting in enhanced electrochemical activity and sites. Further studies of the cellulose pyrolysis mechanism disclose that preoxidation temperature has a crucial influence on the carbon yield and electrical conductivity, which significantly affect the desalination capacity of the integrated (current collector-free and binder-free) POCF electrode. Compared with the conventional activated carbon-coated electrode and commercial activated carbon fibers cloth electrode, the POCF electrode exhibits outstanding desalination performance due to the synergistic effect of high active materials loading and good electrical conductivity. Most importantly, the desalination capacity of POCF electrode realizes the linear growth with 4-fold enhancement by increasing the thickness and remains almost unchanged even up to a large size of 120 cm², indicating unlimited ion diffusion and excellent scalability. Impressively, an ultrahigh areal salt ion adsorption capacity of 0.76 mg cm⁻² is achieved for the 2.4 mm thick POCF electrode. Our work successfully validates the feasibility and superiority of the POCF in constructing thick electrodes for achieving high areal desalination performance.