3D Heterostructure Constructed by Few-Layered MXenes with a MoS₂ Layer as the Shielding Shell for Excellent Hybrid Capacitive Deionization and Enhanced Structural Stability

Abstract

Two-dimensional (2D) layered transition-metal carbides (MXenes) are attractive faradic materials for an efficient capacitive deionization (CDI) process owing to their high capacitance, excellent conductivity, and remarkable ion storage capacity. However, the easy restacking property and spontaneous oxidation in solution by the dissolved oxygen of MXenes greatly restrict their further application in the CDI domain. Herein, a three-dimensional (3D) heterostructure (MoS2@MXene) is rationally designed and constructed, integrating the collective advantages of MXene flakes and MoS2 nanosheets through the hydrothermal method. In such a design, the well-dispersed MXene flakes can effectively reduce the aggregation of MoS2 nanosheets, boost electrical conductivity, and provide efficient charge transfer paths. Furthermore, MoS2 nanosheets as the high-capacity interlayer spacer can prevent the self-restacking of MXene flakes and provide more active sites for ion intercalation. Meanwhile, the strong chemical interactions between MXene flakes and MoS2 nanosheets contribute to accelerating the charge transfer kinetics and enhancing structural stability. Consequently, the resulting MoS2@MXene heterostructure electrode possesses high specific capacitance (171.4 F g–1), fast charge transfer and permeation rate, abundant Na+ diffusion channels, and superior electrochemical stability. Moreover, the hybrid CDI cell (AC//MoS2@MXene) with AC as the anode and MoS2@MXene as the cathode delivers outstanding desalination capacity (35.6 mg g–1), rapid desalination rate (2.6 mg g–1 min–1), excellent charge efficiency (90.2%), and good cyclic stability (96% retention rate). Most importantly, the MoS2@MXene electrode can keep good structural integrity after the long-term repeated desalination process due to the effective shielding effect of the MoS2 layer to protect MXenes from being further oxidized. This work presents the flexible structural engineering to realize excellent ion transfer and storage process by constructing the 3D heterostructure.

Interfacial Charge-Modulated Multifunctional MoS2/Ti3C2Tx Penetrating Electrode for High-Efficiency Freshwater Production

“…Compared with the MoS 2 - or Ti 3 C 2 T x -related materials, MoS 2 /Ti 3 C 2 T x (62.95 mg/g) exhibited a relatively high DC driven by a weak electric field (0.6 V) (Figure a,b and Table S5). ,,− Compared with MoS 2 /Ti 3 C 2 T x , the DC of CF/MoS 2 /Ti 3 C 2 T x was further increased to 83.05–103.12 mg/g (0.6–1.2 V) (Figure c), because MoS 2 /Ti 3 C 2 T x was well-dispersed on the fiber surface, reducing the effect of MoS 2 /Ti 3 C 2 T x aggregation. Meanwhile, the ion adsorption capability of the CF substrate enhanced DC.…”

Recent Progress and Challenges in Faradic Capacitive Desalination: From Mechanism to Performance

“…Reproduced with permission. [ 146 ] Copyright 2022, American Chemical Society. e) Schematic diagram of the CDI process at the mPDA/MXene based electrode.…”

“…According to Figure 14b, MoS 2 /CoS 2 @TNT showed a significantly higher redox peak with Na + adsorption capacity of 44.22 mg g −1 than MoS 2 @TNT and CoS 2 @TNT in HCDI system. Cai et al [ 146 ] constructed a 3D MoS 2 @MXene heterostructure material with an outstanding desalination capacity of 35.6 mg g −1 in a HCDI cell from Figure 14c. As shown in Figure 14d, well‐dispersed MXene flakes can effectively reduce the aggregation of MoS 2 nanosheets, boost electrical conductivity, and provide efficient charge transfer pathways.…”

“…c) Ragone plot of AC//MoS 2 , AC//MXene and AC//MoS 2 @MXene in a NaCl solution of 500 mg L -1 at 1.2 V and d) The coordinative mechanism of MoS 2 and MXene for the structural stability and desalination property of MoS 2 @MXene. Reproduced with permission [146]. Copyright 2022, American Chemical Society.…”

Impact of Faradaic Interlayer Confinement and Carbon‐Centered Macrostructure Designs for Ion Capture and the Recovery of Elements

“…However, the simple oxidation capacity of the carbon anode and the presence of the co-ion expulsion phenomena in the desalination process lead to a loss in desalination capacity and poor cycle stability. [31] In addition, carbon-based materials only offer the EDL model, which restricts the salt absorption capacity. [32] The contact angle goniometry method can be used to quantify the surface wetting of carbon surfaces, where a high water contact angle (WCA > 120°) is typically linked with favorable surface hydrophobicity.…”