DBS−-doped polypyrrole/CNTs with 3D conductive architecture connected with MoS2 as symmetrical electrodes for boosted CDI capability

Abstract

Molybdenum disulfide (MoS2), as an appealing Faradaic material for efficient capacitive deionization (CDI), is limited by unsatisfactory electrical conductivity, inferior removal rate, and restacking. Herein, we develop a CNT/PPy/MoS2 ternary composite using a robust 3D conductive interconnected structure CNT/PPy, constructed from multi-walled carbon nanotubes (MWCNTs) and polypyrrole (PPy) doped with dodecyl benzene sulfonate (DBS-), as the growing substrate to mitigate the aggregation of MoS2 nanoflakes. In this design, CNT/PPy ameliorates the wettability of the composite, provides convenient movement pathways, a fast charge transport rate, and facilitates ions diffusion process. Moreover, reinforced dispersibility and enlarged interlayer spacing of MoS2 nanoflakes supply sufficient embedded sites for ion uptake and rapid transfer. Meanwhile, tight chemical coupling of Mo-N-C bonds can maintain the structural integrity of the composite electrode. Particularly, the symmetrical electrode configuration was established to address the kinetical unbalance of HCDI system. Consequently, the CNT/PPy/MoS2 displays a large specific capacitance of 160.83F g−1 at 5 mV s−1, which is nearly 4.33 times that of MoS2 (37.17F g−1). The optimized CNT/PPy/MoS2 cell achieves a maximum desalination capacity of 24.8 mg g−1, ultra-high deionization rate of 5.24 mg g−1 min−1, and superior capacity retention rate of 92.7 % over 25 cycles. In addition, Na+ ions were captured by the joint action of cation-exchange of DBS--doped PPy, electrostatic adsorption of CNTs, and intercalation reaction of MoS2. The proposed composite structural design and electrode configuration should be a potential avenue to realize highly efficient deionization.