Carbon Dimensionality Engineering in Manganese Oxide Composite Electrodes for High-Efficiency Electrochemical Deionization

Electrochemical deionization (ECDI) has emerged as a promising technology for brackish water treatment and water softening, offering notable advantages in energy efficiency and environmental sustainability. This study systematically investigates the effect of carbon dimensionality on the performance of sodium manganese oxide–carbon composite electrodes (NMO@Cs) for cation capture, in combination with polypyrrole–carbon composites (PPy@Cs) for anion capture. To this end, carbon substrates with distinct dimensionalities—including one-dimensional (1D) carbon nanotubes (CNTs), two-dimensional (2D) reduced graphene oxide (rGO), and three-dimensional (3D) activated carbon (AC) were integrated with sodium pre-intercalated manganese oxide (NMO) to form the NMO@Cs composites. The structural, electrochemical, and desalination performances of these composites are thoroughly characterized and compared. Among the tested configurations, the system with NMO@rGO as the sodium-captured electrode exhibits the highest salt removal capacity (SRC) of 67.2 mg g–1, while the cell using NMO@CNT demonstrates the best cycling stability, retaining 96.8% of its SRC after 200 cycles. The system with NMO@AC shows moderate performance but offers clear cost advantages due to its low material cost and simple processing. Additionally, compared to MnOx, the pre-intercalation of sodium ions stabilizes the layered NMO structure and provides more active sites, enhancing the Na-ion removal capacity and efficiency. Overall, this work provides valuable insights into the rational design of high-performance carbon-based composite electrodes for advanced ECDI applications.