Hybrid Capacitive Deionization Research Articles

Additive-Free, In Situ Rapid Repair of Vacancies in Fe[Fe(CN)6] Electrodes for Efficient Capacitive Deionization.

Fe[Fe(CN)6] (FeHCF) is considered a promising material for capacitive deionization-desalination of saline wastewater due to its excellent structure. However, additives are usually introduced during the synthesis of FeHCF in order to avoid [Fe(CN)6]3- vacancy defects filled by ligand water, which can result in the appearance of harmful byproducts and additional water treatment costs. In this study, an additive-free in situ vacancy repair strategy is proposed for the rapid synthesis of high-quality FeHCF in a saturated K3Fe(CN)6 solution. During the process of synthesizing FeHCF in solution, a high concentration of [Fe(CN)6]3- is found to facilitate the binding of Fe3+ to [Fe(CN)6]3- and hinder the hydrolysis and coordination reaction of Fe3+. After undergoing repair, FeHCF4 demonstrates an increased capacity and highly reversible electrochemical performance due to the robust structure. When utilized as Faraday cathodes in hybrid capacitive deionization (HCDI) systems, FeHCF4 exhibits a higher salt removal capacity (65.67 mg g-1) and lower energy consumption (0.68 kWh kg-1-NaCl) compared to unrepaired FeHCF1, while still maintaining excellent cycling performance. This environmentally friendly approach of repairing vacancies serves as a source of inspiration for the advancement of high-performance Prussian Blue analogues as capacitive sodium-removing materials.

Rational design of MoS2 nanoflowers-decorated carbon nanofibers with enhanced electronic transmission for boosting capacitive deionization

Capacitive deionization (CDI) has sparked considerable interest for its promising application in handling brackish water. Unfortunately, most traditional carbonaceous materials are still plagued by the limited desalination capacity and sluggish adsorption kinetics with the single adsorption mechanism and irrational pore structure. Herein, we developed a facile and affordable strategy to integrate electrospinning with hydrothermal method to fabricate MoS2 nanoflowers-decorated carbon nanofibers (MoS2/CNF) composite for boosting desalination performance. CNF not only serves as a supportive framework to inhibit the agglomeration of MoS2 nanosheets favoring the full contact with salt solutions, but also typically diminishes the charge transfer resistance of the composite. By taking advantage of the double layer adsorption of CNF and the hierarchically micro-mesoporous structure of MoS2 nanoflowers with large interlayer spacer for salt ions intercalation, the optimized sample MoS2/CNF-1 employed as a cathode for the asymmetric hybrid CDI cell showed an eminent capacity for desalination of 30.9mg·g-1, an ultrafast rate for desalination of 3.7mg·g-1·min-1, and an attractive circulation stability for desalination with the capacity reservation remaining at 94.8% after 30 cycles in the solution of 500mg·L-1 NaCl at 1.2V. This research sheds fresh light on the evolution of advanced CDI electrode materials for practical utilization.

In-situ growth of Ni, Co-Prussian blue nanocubes on molten salt etched lamellar Ti3C2Tx/Ni for enhanced hybrid capacitive deionization

The design and development of high-performance electrode materials are crucial for improving the desalination efficiency of hybrid capacitive deionization (HCDI). In this study, a Ti3C2Tx/Ni/NiCo-PBA composite is synthesized by in-situ growing NiCo Prussian blue (PB) nanocubes on Ti3C2Tx/Ni sheets, serving as an electrode for HCDI. The Ti3C2Tx sheets provide excellent conductivity and a suitable substrate for the growth of NiCo-PBA nanocubes. The Ni nanoparticles help prevent the oxidation of Ti3C2Tx sheets, and provide a source of Ni for NiCo-PBA synthesis. Additionally, the NiCo-PBA nanocubes effectively inhibit re-stacking of Ti3C2Tx sheets, enlarge crystal lattice spacing, and facilitate diffusion and storage of salt ions. Consequently, the AC||Ti3C2Tx/Ni/NiCo-PBA HCDI device exhibits a high salt removal capacity of 36.62 mg g−1, low energy consumption of 11.14 Wh m−3, and water recovery of 61.86 %. Importantly, the AC||Ti3C2Tx/Ni/NiCo-PBA device achieves a good salt removal capacity of 53.22 mg g−1 in a high concentration NaCl solution (2000 μS cm−1). After 20 cycles, the desalination capacity remains stable, and the structure of Ti3C2Tx/Ni/NiCo-PBA is intact, indicating excellent cycling stability. Additionally, the desalination mechanism of Ti3C2Tx/Ni/NiCo-PBA electrode is thoroughly investigated.

Long-acting electrochemical lithium-recovery from original brine using super-stable spinel lithium manganate oxide

with the unprecedented demand for raw lithium, the spinel LiMn2O4 has been widely studied for electrochemical Li-recovery from salt-lake brines, but its industrialization is hindered by the poor cyclability induced by manganese dissolution and Jahn-Teller distortion within octahedral structure. In this work, Cr-doped and carbon-coated LiMn2O4 (C-LMO-Cr) electrodes prepared via coprecipitation-calcination method are employed to improve cycling stability and lithium selectivity for electrochemical Li-recovery. The results confirm the C-LMO-Cr electrode exhibits super-high retention rate of 98.76 % and 95.70 % of the initial capacity (27 mg·g−1) after 300 and 500 cycles, respectively. The carbon buffering on the C-LMO-Cr surface effectively impedes the initial manganese dissolution with the enhanced charge transfer. Moreover, the structural evolution from Raman/XPS analysis and theoretical calculations confirms that the shrinking lattice of the carbon-buffering LMO-Cr enhances Li+ selectivity and Li+ migration. When assembled in a hybrid capacitive deionization (HCDI) device, the optimal C-LMO-Cr electrode displays high adsorption capacity of ∼21 mg·g−1, moderate energy consumption of 13 Wh·mol−1(Li+) with a remarkable increase in Mg/Li ratio from 1.67 to 158 in the original brine from Jiezechaka. Therefore, these results demonstrate a promising potential of C-LMO-Cr electrodes for long-acting electrochemical lithium-recovery from original brines.

Accelerating ion diffusion kinetics with an intensified interfacial electric field for efficient hybrid capacitive deionization

The interfacial electric field (IEF) represents a cutting-edge strategy for enhancing ion diffusion kinetics, pivotal in various technological applications. Despite its extensive use, the mechanisms and strategies for regulating IEF remain underexplored. In this study, we enhanced the IEF in a MnO2-x/g-C3N4 (CN) heterostructure by engineering oxygen vacancies in MnO2, which increased the work function difference between MnO2 and CN. The increased work function difference effectively lowers the energy barrier for electron transfer at the heterostructure interface, thereby intensifying the IEF. The enhanced IEF subsequently provides a more potent driving force, facilitating ion movement within the electrode materials during the desalination process. The modified MnO2-x/CN heterostructure demonstrates a notable salt removal capacity of 45.5 mg g−1 and an impressive salt removal rate of 4 mg g−1 min−1, under an operational voltage of 1.2 V in a 500 mg/L NaCl solution. This research not only deepens our understanding of IEF modulation in materials but also sets the stage for the development of high-performance electrodes for hybrid capacitive deionization systems.

Seed strategy synthesis of porous NASICON structured NaTi2(PO4)3/carbon aerogel nanocomposites for high-performance hybrid capacitive deionization

The limited capacity of conventional carbon electrode materials hinders the practical application of capacitive deionization (CDI). Hence, it is imperative to develop electrode materials with high sodium ion adsorption and reliable stability to facilitate the construction of hybrid CDI (HCDI) systems. Notably, NaTi2(PO4)3 (NTP) has received significant attention due to its high capacity and rapid transportation ability of sodium ions. However, the poor electrical conductivity and limited electrolyte contact area of NTP have prevented further improvement in its deionization capacity. Herein, we report a seed strategy to synthesize NTP/carbon aerogel (CA). P25 was used as a seed crystal to prepare TiO2/CA via the sol–gel method and supercritical CO2 drying. NTP/CA was then obtained from TiO2/CA by hydrothermal synthesis and calcination. This strategy preserved the rational network skeleton of CA and endowed NTP/CA with a high specific surface area of 420 m2/g. The enhanced electrical conductivity provided by CA yielded a remarkable salt adsorption capacity of 43.3 mg/g in a 500 mg/L NaCl solution and a stable cycle desalination capability. This work provides a new perspective for constructing three-dimensional, highly efficient and stable HCDI electrode materials.

Preparation of layered structure MnO2/CNTs composites for high-performance salt removal by hybrid capacitive deionization

Preparation of layered structure MnO2/CNTs composites for high-performance salt removal by hybrid capacitive deionization

Polyaniline modified exfoliated graphene aerogel as high-performance anion-capture electrode for hybrid capacitive deionization

The synergistic effect between polyaniline (PANI) and graphene nanosheets significantly enhances the monolithic capacitance and cycling stability, making it an attractive choice for use as an anode material in capacitive deionization (CDI). However, traditional preparation processes are usually complex and time-consuming. Herein, we proposed a simplified solid-phase strategy by using air-plasma technique to fabricate 3D puffy graphene aerogel supported PANI (PANI@PG) nanocomposites within 1 s. In this material, elongated dumbbell-shaped PANI particles with diameters of 30–60 nm were firmly anchored and highly dispersed on graphene sheets, meanwhile, the exfoliated graphene sheets with a large interlayer distance of 0.4 nm were well interconnected. It was demonstrated that as prepared PANI@PG is characteristic of 2–50 nm mesopores, which both ensures a sufficient exposure of PANI active sites to electrolyte and favors the Cl− diffusion-intercalation process. The freestanding PANI@PG electrode exhibited excellent figure-of-merits of the salt adsorption capacity (43.5 mg g−1), charge efficiency (88.6 %), and cycling stability (retention of 77.1 % after 40 cycles). This work paves a new way for constructing 3D conducting polymer/graphene nanocomposites with promising applications in CDI and beyond.

Efficient fluoride removal in hybrid capacitive deionization enabled by Ce-Zn-MOF-derived CeO2@C and birnessite electrodes

Fluorine pollution has become a public health issue of global concern. Capacitive deionization (CDI) presents the benefits of simple operation, high energy efficiency, and good sustainability. The development of high adsorption performance, economical and environmentally friendly defluorination electrodes is the key direction of capacitive deionization. Here, a spherical metal–organic framework (MOF) Ce/Zn-BTC was prepared by solvothermal method utilizing benzene-tricarboxylic (BTC) acid as solvent, and then it was transformed into CeO2@C composites through pyrolysis. The spherical structure of the original MOFs is preserved by CeO2@C, leading to significant enhancements in specific surface area (275.48 m2/g), pore volume (0.3359 cm3/g), and electrochemical performance. In this work, the anode material CeO2@C was employed for the first time, while birnessite-type MnO2 (δ-MnO2) was utilized as a cathode material for the fabrication of a hybrid CDI (HCDI) device for the treatment of fluorinated wastewater. The CeO2@C/δ-MnO2 cell shows excellent fluoride removal performance with a removal capacity of 22.03 mg/g for 50 mg/L fluoride solutions under a 1.2 V applied voltage, which is better than most carbon-based materials. Importantly, the CeO2@C/δ-MnO2 cell has favorable fluoride selectivity and regeneration performance (>75 %) even after undergoing ten cycles. Fluoride is mainly removed by intercalation into the carbon skeleton, coordination with Ce, and electrostatic interaction. This study shows that the CeO2@C/δ-MnO2 cell has excellent fluoride removal performance and practical application prospects.

Imine-based conjugated polymer enables efficient removal of ammonium ion via capacitive deionization

The design of innovative faradaic electrode materials is crucial for improving the removal efficiency of contaminants in hybrid capacitive deionization (HCDI) systems. Organic compounds are a promising choice for faraday electrodes due to the sustainable production and tunable molecular structure. However, their high solubility in aqueous media and limited availability of redox-active sites for deionization greatly constrain the HCDI applications. Herein, we intentionally construct a conjugated polymer (IMP) with abundant imine groups, in which the strategic integration of N-heteroaromatic rings within the π-conjugated framework effectively prevents the disintegration of redox-active entities, while honing the energy bandgap and electronic characteristics. The copious redox-active CN sites within the imine groups along the polymeric chain markedly improve its capacity for the high-efficiency (de)intercalation of NH4+ ions. As an electrode material, the IMP polymer exhibits a significant NH4+-storage capacitance of 257.1 F g−1 at 2 A g−1 and maintains an ultra-cycle stability of 96.1 % after 10,000 cycles (4 A g−1), as evidenced by the in-situ spectral analysis of electrolyte. For real applications, a HCDI configuration has been constructed with a high specific NH4+ adsorption capacity of 119.0 mg g−1 and a fast removal rate of 27.0 mg g−1 min−1 with stable regeneration performance.

Manganese doping strategy for enhanced capacitive deionization performance of MoS2

Molybdenum disulfide (MoS2) has gained enormous attention as the electrode for capacitive deionization (CDI) by virtue of its fascinating layer structure and ion storage property. However, the sluggish intrinsic conductivity and limited ion storage capacity of MoS2 hampered their practical applications. In this work, a manganese doping strategy via a one-step hydrothermal process was adopted to fabricate manganese-doped MoS2 nanosheets (Mn-MoS2) for efficient capacitive desalination. It is shown that Mn-MoS2 presents an enlarged interlamellar spacing, enriched mesoporous structure, and excellent hydrophilicity. When used as a working electrode in a hybrid CDI cell, Mn-MoS2 delivered an outstanding salt removal capacity of 24.5 mg g−1 in a 500 mg L−1 NaCl solution. Notably, Mn-MoS2 presented fast kinetics in the desalination process, which reached equilibrium in 8 minutes with a removal rate of 3.06 mg g−1 min−1 and superior stability after 30 cycles, which outperformed the performance of most MoS2 based CDI electrode. XPS spectra indicated that the electronic structure of MoS2 could be modulated by Mn doping to generate 1 T phase, which further improved the intrinsic activity and ion storage capacity. This study paves a way for the design of MoS2 and its application in outstanding performance and durable CDI cell.

Plasma-assisted preparation of NiCoAl-layered double hydroxides with alarge interlayer spacing on carbon cloth forelectrochemical deionization

Capacitive deionization has been considered an emerging desalination technique in recent years, especially for its economic and energy-saving characteristics for brackish water. However, there are currently few studies on chloride ion removal electrodes, and the slow desalination kinetics limits their development. Ar-NiCoAl- layered double hydroxide (LDH)@ACC materials with an increased interlayer spacing were prepared by the in-situ growth of NiCoAl-LDHs nanosheet arrays on acid-treated carbon cloth (ACC) and subsequent Ar plasma treatment. The carbon cloth suppresses the agglomeration of the NiCoAl-LDHs nanosheets and improves the electrical conductivity, while the plasma treatment increases the interlayer spacing of NiCoAl-LDHs and improves its hydrophilicity. This provides rapid diffusion channels and more interlayer active sites for chloride ions, achieving high desalination kinetics. A hybrid capacitive deionization (HCDI) cell was assembled using Ar-NiCoAl-LDHs@ACC as the chloride ion removal electrode and activated carbon as the sodium ion removal electrode. This HCDI cell achieved a high desalination capacity of 93.26 mg g−1 at 1.2 V in a 1000 mg L−1 NaCl solution, a remarkable desalination rate of 0.27 mg g−1 s−1, and a good charge efficiency of 0.97. The capacity retention remained above 85% after 100 cycles in a 300 mg L−1 NaCl solution at 0.8 V. The work provides new ideas for the controlled preparation of two-dimensional metal hydroxide materials with a large interlayer spacing and the design of high-performance electrochemical chlorine ion removal electrodes.

Half-disturbed spin desalination: Asymmetric high-spin states in MnO2 accelerate charge transfer in capacitive deionization

Manganese dioxide (MnO2) has been recognized for its high theoretical capacitance. Recent advancements highlight the potential of modulating the spin state of Mn to elevate charge transfer kinetics. Nonetheless, the specific relationship between Mn spin distribution and desalination efficacy, alongside the underlying mechanism, remains elusive. This study introduces the novel concept of half-disturbed spin desalination, elucidating its complex mechanism via the strategic induction of oxygen vacancies on the MnO2 surface. Theoretical analyses reveal that electron transfer from the O py (up) and pz (up) to the Mn dz2 (up) orbitals alters MnO2's spin state from a symmetric low spin to an asymmetric high spin configuration. This transition disrupts spin up symmetry, bolstering dynamic processes and diminishing the ion diffusion energy barrier. Consequently, oxygen vacancy-enriched MnO2 (VO-MnO2) demonstrates an enhanced specific capacitance of 289 F g−1 at 1 A g−1. Remarkably, in the hybrid capacitive deionization (HCDI) process, it achieves a superior salt adsorption capacity (SAC) of 56.5 mg g−1 and a salt adsorption rate (SAR) of 2.5 mg g−1 min−1. This research pioneers the correlation between spin desalination mechanisms and spin state applications, paving the way for novel applications across diverse fields.

Scalable NH4V4O10 clusters as functional network nodes on toughened porous carbon nanofibers for hybrid capacitive deionization

Layered vanadium-based compound (e.g., NH4V4O10) is acknowledged as an outstanding candidate for intercalation pseudocapacitance electrode of capacitive deionization (CDI) cells. However, the directed production of high-efficiency NH4V4O10-based self-supporting CDI electrodes and their structure–activity connection warrant more in-depth study. Herein, the delicate design and controllable construction of NH4V4O10 clusters on the freestanding porous carbon nanofiber (PCNF) scaffolds (the composite PCNFs/NH4V4O10 is defined as CNVO) using a new organic reducing agent of citric acid is proposed, where NH4V4O10 clusters as functional network nodes can improve the mechanical toughness, electrochemical capacitive performance, and desalination capability of the CNVO hybrid. The Na+ adsorption mechanism on CNVO is confirmed by ex-situ experimental characterizations and density functional theory (DFT) calculations. The hybrid CDI (HCDI) cell composed of the optimized CNVO cathode and PCNFs anode shows a desirable desalination capacity (45.07 mg g−1), a superior salt removal rate (16.4 mg g−1 min−1), an excellent energy utilization, and an acceptable cyclic regeneration ability in 500 mg L-1 NaCl solution. More importantly, the assembled HCDI system is promising for the desalination of reclaimed water from the printing and dyeing enterprise. This work highlights a scalable strategy that is experimentally and theoretically feasible to design and fabricate high-efficiency CDI electrodes.

Improved Na+ adsorption performance and storage mechanism of cobalt hexacyanoferrate/polyaniline composite during the hybrid capacitive deionization process

In order to realize high desalting capacity of capacitive deionization (CDI) system, cobalt hexacyanoferrate/polyaniline (CoHCF/PANI) composite with hollow hierarchical tubular structure was finely prepared by employing conductive hollow PANI tube as the interconnection skeleton for CoHCF cubic particles grown in situ, thereby endowing this composite with good conductivity, abundant redox active sites and stable structure. The synergistic effect between the CoHCF layer and PANI layer makes the CoHCF/PANI electrode possess superior specific capacitance (263.8F·g−1) and high contribution of the capacitance behavior (87.8 %) at 5 mV·s−1. Compared with either the single PANI or CoHCF electrode, the CoHCF/PANI electrode exhibits outstanding salt adsorption capacity (30.48 mg·g−1), rapid salt adsorption rate (3.66 mg·g−1·min−1) and excellent cycle stability (retention rate 98.1 %). Different from the CoHCF/PANI(+)‖AC(−) cell, there is no inversion peak in the AC(+)‖CoHCF/PANI(−) cell, which testifies that the CoHCF/PANI electrode is easier to capture Na+ ions. Based on the XPS spectra before and after desalination tests, the Na+ adsorption mechanism of the CoHCF/PANI electrode as cathode for the hybrid capacitive deionization (HCDI) system was further explored. It is found that the change of element valence in CoHCF/PANI composites (reduction of Fe3+ to Fe2+ and Co3+ to Co2+ in CoHCF, partial reduction of −C = N+ to −N–H- in PANI) is the main factor leading to Na+ intercalation. This study emphasizes the significance for fine design of the electrode material and strategic configuration of the HCDI cell.

Unveiling the role of Atomic-Level “Pump-Driven” effect in MoS2/MnO2 for facilitating directional charge transfer in hybrid capacitive deionization

In addressing the limitations imposed by the inherently low electronic conductivity and substantial ion transfer resistance of transition metal oxides (TMOs) in hybrid capacitive deionization (HCDI) applications, this study delineates a pioneering approach through the fabrication of a MoS2/MnO2 heterostructure, leveraging manganese dioxide (MnO2) as a model system. The investigation underscores the essentiality of constructing high-quality interfaces to act as conduits for directional charge flow, a critical but formidable challenge for enhancing desalination efficacy in electrode materials. By harnessing an atomistic “pump-driven” mechanism, the MoS2/MnO2 heterostructure demonstrably facilitates the promotion of desalination processes, underscored by the establishment of a potent local electric field (IEF) aimed at commanding charge dynamics. Empirical and computational analyses coalesce to unveil the preferential electron transfer from MoS2 to MnO2, a phenomenon precipitated by charge redistribution. This orchestrated charge flow not only augments electronic and ionic transfer efficiencies but also emboldens the MoS2/MnO2 heterostructure with enhanced desalination capabilities. The results show that MoS2/MnO2 demonstrates superior HCDI performance compared to MnO2 in a 500 mg L-1 NaCl solution at 1.2 V, with SRC of 33.21 mg g-1 and SRR of 1.50 mg g-1 min-1. The elucidation of this charge-guided dynamic, achieved through meticulous manipulation of the electronic microstructure and the IEF at the atomic scale, presents a novel paradigm for material science. This research presents an innovative approach for realizing robust charge-guided dynamics through the deliberate manipulation of the electronic microstructure and IEF of materials, employing an atomic-level “pump-driven” effect. This strategy opens new avenues for extending these principles to a broad array of advanced materials.

Fabrication of cathode electrodes based on activated carbon, reduced-graphene for hybrid capacitive deionization technology

Abstract Recently, hybrid capacitive deionization (HCDI) has been a promising desalination technology because of its low cost and effective ion removal ability. The electrode material is an important factor to affect to desalination capacity of HCDI technology. In this study, the nanocomposite electrodes were fabricated successfully based on activated carbon and reduced-graphene oxide/cobalt oxide (rGO-Co3O4) and polymeric binders which were used as cathode electrodes for Hybrid capacitive deionization (HCDI) technology. The effect of polyvinyl alcohol (PVA) and polyvinylidene fluoride (PVDF) polymeric binders and the amount of rGO-Co3O4 on characteristic as well as specific capacitance of the nanocomposite electrodes were investigated. The nanocomposite electrode combined hydrophilic binder of PVA-based and 50 % rGO-Co3O4 has a specific capacitance of 15.3 mg/g in 200 ppm NaCl solution after 25 min at 1.2 V, which is 1.67 times higher than that of the AC-based electrode.

Rational design of Core-Shell heterostructured CoFe@NiFe Prussian blue analogues for efficient capacitive deionization

Rational design of stable and high-capacity faradaic electrode materials is crucial for enhancing the desalination performance of hybrid capacitive deionization (HCDI). In this work, to fully exploit the advantages of high-capacity CoFe Prussian blue analogs (PBA) and structurally stable NiFe PBA, a core–shell heterostructured CoFe@NiFe PBA is successfully synthesized by a two-step co-precipitation method. The construction of the core–shell heterostructure not only suppresses dissolution of the CoFe PBA core, but also facilitates fast charge transfer and efficient ion diffusion during Na+ ions insertion/extraction. With an optimal NiFe PBA shell thickness of 30 nm, the core–shell structured PBA electrode demonstrates outstanding cycling performance with a capacity retention of 72.6 % over 10,000 charge/discharge cycles. Moreover, when utilized as the cathode material in HCDI, the core–shell heterostructured PBA exhibits intriguing desalination performance, including a high desalination capacity of 49 mg g−1 and excellent desalination stability over 200 cycles (77.7 %). This paper presents a straightforward strategy for designing core–shell heterostructured PBA electrode, with the potential to advance the development of high-performance capacitive desalination.

Na2MnSiO4/C as hybrid capacitive deionization electrode material to enhance desalination performance

The utilization of Na2MnSiO4 as a Faraday electrode in hybrid capacitive deionization (HCDI) is investigated to achieve efficient desalination. The Na2MnSiO4/C (NMSO) materials were fabricated via a simple sol–gel method, in which the synthesis process was modulated by adjusting the volume ratio of ethanol to water. When maintaining the volume ratio of water to ethanol at 3:1, the resultant NMSO-3/1 exhibited expected salt adsorption capacity of 31.06 mg g−1 and salt adsorption rate of 20.43 mg g−1 min−1. This distinguished desalination performance was mainly attributed to its inherent multiple redox pairs, as well as the integration of ethanol, which enhanced both specific capacitance and hydrophilicity of the material. This study opens a new perspective for the development of highly efficient materials in HCDI.

Synthesis of novel 2D/2D Ti3C2Tx MXene / 1T-MoS2 heterostructure enhanced with carbon nanotubes as a highly-efficient electrode for hybrid capacitive deionization

MXenes are a prominent group within 2D materials with extensive utilization in various electrochemical applications due to their notable specific capacitance, swift ion intercalation kinetics, and favorable hydrophilicity. Despite this, they suffer from low oxidation resistance and ease of layer restacking. Herein, an effective approach to overcome this inherent weakness of MXenes was employed by embedding MoS2 nanopetals as pillars into the backbone of Ti3C2Tx MXene by a one-step hydrothermal technique. It not only alleviates the restacking problem of Ti3C2Tx but also shorten the diffusion path of sodium ions. Meanwhile, ammonium bicarbonate as a guest ion agent was utilized to achieve the 1 T phase of MoS2 with numerous edge-active sites to overcome the low electrical conductivity of the 2 H phase derived from the semiconducting nature. The incorporation of carbon nanotubes (CNTs) has strengthened the structural integrity of the Ti3C2Tx/1 T-MoS2/CNTs composite by linking 2D material components. Moreover, it elevates the heterostructure’s overall electrical conductivity by establishing multiple routes for efficient electron transfer. As a result, the membrane-free established hybrid capacitive deionization cell with Ti3C2Tx/1 T-MoS2/CNTs // activated carbon demonstrates a remarkable salt removal capacity of 25.82 mg.g−1 along with an outstanding high removal rate of 5.25 mg.g−1.min−1 and superior cyclic stability (98.1% desalination capacity retention rate). This work represents a simple approach for rational designing low-dimensional heterostructure materials with high connectivity and straightforward electron transferring for electrochemical desalination.