Abstract
Flow electrode capacitive deionization (FCDI) offers a potential solution to desalinate brackish water efficiently with low energy consumption. Optimizing the flow electrode materials is essential for improving the FCDI performance. Carbon black (CB) slurry is an ideal candidate for use as flow electrode, owing to its excellent conductivity and large specific surface that benefit with efficient ion capacitive adsorption processes. However, the agglomeration and sedimentation issues of CB nanoparticles in aqueous electrolyte caused an instability of the flow electrode, which remained an obstacle of this desalination technology. We present in this study a new strategy to overcome this challenge by modifying CB particle surface with direct blue (DB) molecules. The modified CB slurry exhibited an outstanding stability, with little sedimentation after 24 h of still stay as compared to significant sedimentation of the bare CB slurry within 5 min. The dramatically improved stability was attributed to a strong adsorption of DB molecules to CB particle surface, with their sulfonate functional groups enhancing the surface hydrophilicity and thus stabilizing CB particles in aqueous electrolyte. Efficient, durable water desalination was achieved using the new flow electrode, with as high as 53.43 mu g cm-2 min-1 average salt removal rate (ASRR), a low 1.83 J mg-1 electrical energy consumption (EEC) and outstanding durability being obtained using FCDI with 0.01 M/5M DB/CB flow electrode. The findings validate the DB/CB flow electrode strategy for overcoming the instability problem and offer a new direction for advancing FCDI technology in water desalination applications.