Fabrication of mesoporous graphene electrodes with enhanced capacitive deionization

Hierarchical porous metal–organic gels and derived materials: from fundamentals to potential applications

This review summarizes recent progress in the development and applications of metal–organic gels (MOGs) and their hybrids and derivatives dividing them into subclasses and discussing their synthesis, design and structure–property relationship.

Novel mesoporous Co3O4-Sb2O3-SnO2 active material in high-performance capacitive deionization

Capacitive deionization (CDI), as an emerging eco-friendly electrochemical brackish water deionization technology, has widely benefited from carbon/metal oxide composite electrodes. However, this technique still requires further development of the electrode materials to tackle the ion removal capacity/rate issues. In the present work, we introduce a novel active carbon (AC)/Co₃O₄-Sb₂O₃-SnO₂ active material for hybrid electrode capacitive deionization (HECDI) systems. The structure and morphology of the developed electrodes were determined using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Brunauer-Emmett-Teller (BET)/Barrett-Joyner-Halenda (BJH) techniques, as well as Fourier-transform infrared (FT-IR) spectroscopy. The electrochemical properties were also investigated by cyclic voltammetry (CV) and impedance spectroscopy (EIS). The CDI active materials AC/Co₃O₄ and AC/Co₃O₄-Sb₂O₃-SnO₂ showed a high specific capacity of 96 and 124 F g^-1 at the scan rate of 10 mV s^-1, respectively. In addition, the newly-developed electrode AC/Co₃O₄-Sb₂O₃-SnO₂ showed high capacity retention of 97.2% after 2000 cycles at 100 mV s^-1. Moreover, the electrode displayed excellent CDI performance with an ion removal capacity of 52 mg g^-1 at the applied voltage of 1.6 V and in a solution of potable water with initial electrical conductivity of 950 μs cm^-1. The electrode displayed a high ion removal rate of 7.1 mg g^-1 min^-1 with an excellent desalination-regeneration capability while retaining about 99.5% of its ion removal capacity even after 100 CDI cycles.

Efficiency Enhancement of Electro-Adsorption Desalination Using Iron Oxide Nanoparticle-Incorporated Activated Carbon Nanocomposite

Capacitive deionization (CDI) technology is currently considered a potential candidate for brackish water desalination. In this study, we designed iron oxide nanoparticle-incorporated activated carbon (AC/Fe₂O₃) via a facile and cost-effective hydrothermal process. The as-synthesized material was characterized using several techniques and tested as electrodes in CDI applications. We found that the distinctive properties of the AC/Fe₂O₃ electrode, i.e., high wettability, high surface area, unique structural morphology, and high conductivity, resulted in promising CDI performance. The electrosorptive capacity of the AC/Fe₂O₃ nanocomposite reached 6.76 mg g^-1 in the CDI process, with a high specific capacitance of 1157.5 F g^-1 at 10 mV s^-1 in a 1 M NaCl electrolyte. This study confirms the potential use of AC/Fe₂O₃ nanocomposites as viable electrode materials in CDI and other electrochemical applications.

Fabrication of polyvinylidene fluoride-derived porous carbon heterostructure with inserted carbon nanotube via phase-inversion coupled with annealing for capacitive deionization application

As a promising desalination technology, capacitive deionization (CDI) has great potential to guarantee freshwater supply. It is urgently needed to explore novel electrode materials with excellent desalination performance. Herein, the PVDF-derived porous carbon heterostructure with inserted carbon nanotube (PPC/CNT) was prepared via phase-inversion coupled with annealing strategy and applied as electrode material for CDI desalination. The resultant PPC/CNT possesses the combined structural advantages of PPC and CNT, such as high specific surface, mesoporous structure and improved conductivity. By virtue of these remarkable properties, PPC/CNT exhibites an excellent electrosorption capacity of 15.1 mg/g in 500 mg/L NaCl, while that of PPC electrode is 10.3 mg/g. Specially, the charge efficiency of PPC/CNT electrode is 1.39 times higher as compared to PPC, which is largely responsible for the improvement of electrosorption capacity. Besides, PPC/CNT electrode demonstrated good cycle stability over 10 electrosorption-desorption cycles. Thus, PPC/CNT electrode presents promising prospects as CDI electrode for water desalination. This work may shed new light on the rational design of porous carbon heterostructures with suitable host matrix and improved conductivity, subsequently developing the CDI performance.

Sustainable Desalination by 3:1 Reduced Graphene Oxide/Titanium Dioxide Nanotubes (rGO/TiONTs) Composite via Capacitive Deionization at Different Sodium Chloride Concentrations

The capability of novel 3:1 reduced graphene oxide/titanium dioxide nanotubes (rGO/TiONTs) composite to desalinate using capacitive deionization (CDI) employing highly concentrated NaCl solutions was tested in this study. Parameters such as material wettability, electrosorption capacity, charge efficiency, energy consumption, and charge-discharge retention were tested at different NaCl initial concentrations—100 ppm, 2000 ppm, 15,000 ppm, and 30,000 ppm. The rGO/TiONTs composite showed good material wettability before and after CDI runs with its contact angles equal to 52.11° and 56.07°, respectively. Its two-hour electrosorption capacity during CDI at 30,000 ppm NaCl influent increased 1.34-fold compared to 100 ppm initial NaCl influent with energy consumption constant at 1.11 kWh per kg with NaCl removed. However, the percentage discharge (concentration-independent) at zero-voltage ranged from 4.9–7.27% only after 30 min of desorption. Repeated charge/discharge at different amperes showed that the slowest charging rate of 0.1 A·g⁻¹ had the highest charging time retention at 60% after 100 cycles. Increased concentration likewise increases charging time retention. With this consistent performance of a CDI system utilizing rGO/TiONTs composite, even at 30,000 ppm and 100 cycles, it can be a sustainable alternative desalination technology, especially if a low charging current with reverse voltage discharge is set for a longer operation.

Various cell architectures of capacitive deionization: Recent advances and future trends

Substantial consumption and widespread contamination of the available freshwater resources necessitate a continuing search for sustainable, cost-effective and energy-efficient technologies for reclaiming this valuable life-sustaining liquid. With these key advantages, capacitive deionization (CDI) has emerged as a promising technology for the facile removal of ions or other charged species from aqueous solutions via capacitive effects or Faradaic interactions, and is currently being actively explored for water treatment with particular applications in water desalination and wastewater remediation. Over the past decade, the CDI research field has progressed enormously with a constant spring-up of various cell architectures assembled with either capacitive electrodes or battery electrodes, specifically including flow-by CDI, membrane CDI, flow-through CDI, inverted CDI, flow-electrode CDI, hybrid CDI, desalination battery and cation intercalation desalination. This article presents a timely and comprehensive review on the recent advances of various CDI cell architectures, particularly the flow-by CDI and membrane CDI with their key research activities subdivided into materials, application, operational mode, cell design, Faradaic reactions and theoretical models. Moreover, we discuss the challenges remaining in the understanding and perfection of various CDI cell architectures and put forward the prospects and directions for CDI future development.

Moderately oxidized graphene–carbon nanotubes hybrid for high performance capacitive deionization

Moderately oxidized graphene–carbon nanotubes hybrid can be used as good electrode materials for CDI with enhanced electrosorption capacity.