Three-dimensional (3D) MnMoO₄@g-C₃N₄/CNT hybrid composite electrode for hybrid capacitive deionization

In this work, a hierarchical three-dimensional MnMoO₄@g-C₃N₄/CNT hybrid ternary composite was developed through the facile hydrothermal method. MnMoO₄@g-C₃N₄/CNT and g-C₃N₄/CNT electrodes were used as cathode and anode to fabricate the hybrid capacitive deionization (HCDI) system. Manganese molybdate (MnMoO₄) rods are uniformly intertwined on the three-dimensional (3D) conductive network structure of graphitic carbon nitride/carbon nanotube (g-C₃N₄/CNT) heterojunction in the ternary composite. As-obtained electrode materials of MnMoO₄@g-C₃N₄/CNT and g-C₃N₄/CNT show the specific capacitance of 252.4 and 89.2 Fg⁻¹, respectively, at 1 Ag⁻¹ in 1 M NaCl solution. Mn element in the MnMoO₄@g-C₃N₄/CNT hybrid induces a reversible redox reaction that selectively intercalates/de-intercalates the Na⁺-ion in the salt solution, yielding a high salt adsorption capacity of 43.6 mg. g⁻¹ at 1.2 V and 1000 ppm NaCl solution medium. In addition, MnMoO₄@g-C₃N₄/CNT //g-C₃N₄/CNT-based HCDI cell was recycled for 10 cycles. The system reaches the highest SAC of 42.6 mg. g⁻¹ after 10 consecutive charge–discharge cycles with a retention of 91%, indicating the excellent cycling stability of the MnMoO₄@g-C₃N₄/CNT electrode. These results signify that the MnMoO₄@g-C₃N₄/CNT is a promising electrode material, possessing a pseudocapacitive behavior and remarkable desalination ability, which can be a potential new candidate for the HCDI system.