Ultrathin MoS₂-Decorated N-Doped Carbon with Hierarchical Porosity for High-Capacity, Low-Energy Capacitive Deionization with Outstanding Cycling Stability

Abstract

The escalating demand for freshwater and the high energy footprint of conventional desalination technologies have driven the development of advanced electrode materials for capacitive deionization (CDI). Despite their widespread use, traditional carbon electrodes often suffer from limited electrosorption capacity, co-ion expulsion, and insufficient surface functionality. Herein, we present a hierarchical molybdenum disulfide–nitrogen-doped carbon (MoS₂–NDC) composite engineered to address these challenges through coupled structural and interfacial design. The material comprises ultrathin, wrinkled nitrogen-doped carbon nanosheets uniformly decorated with nanocrystalline hexagonal MoS₂ domains. This architecture inhibits nanosheet restacking, establishes a continuous conductive framework, and introduces negatively charged, electroactive surfaces that enhance selective cation adsorption. Comprehensive structural and spectroscopic analyses confirm preserved MoS₂ crystallinity, strong MoS₂–carbon interfacial coupling, and abundant redox-active Mo and S species. Nitrogen incorporation and hierarchical porosity yield a high specific surface area (323.2 m² g⁻¹) and abundant accessible adsorption sites, while contact-angle measurements reveal improved hydrophilicity, facilitating rapid ion transport. Electrochemical characterization demonstrates enhanced conductivity, substantial charge storage capability, and a stable potential of zero charge (~0.35 V), accompanied by progressive surface activation during cycling. When evaluated as CDI electrodes, the MoS₂–NDC composite delivers a high salt adsorption capacity of 42.9 mg g⁻¹ at 1.4 V, a low specific energy consumption of 11.7 Wh kg⁻¹, and stable desalination performance over 350 cycles. In addition, testing in MgSO₄ and CaCl₂ electrolytes show effective ion removal of 23.8 mg.g⁻¹ and 10.7 mg.g⁻¹ at 100 mg/L , confirming the electrode’s strong performance across different cation types. The superior performance is attributed to synergistic effects arising from expanded MoS₂ interlayer spacing, conductive N-doped carbon networks, improved wettability, and hierarchical pore architecture, collectively enabling efficient ion transport and storage. This work highlights the potential of heterostructured transition metal dichalcogenide–carbon composites as scalable, high-performance electrodes for energy-efficient water desalination.