A novel graphene oxide-based ceramic composite as an efficient electrode for capacitive deionization

Activated carbon derived from the date palm leaflets as multifunctional electrodes in capacitive deionization system

Among various desalination technologies, capacitive deionization (CDI) has rapidly developed because of its low energy consumption and environmental compatibility, among other factors. Traditional CDI stores ions within the electric double layers (EDLs) in the nanopores of the carbon electrode, but carbon anode oxidation, the co-ion expulsion effect, and a low salt adsorption capacity (SAC) block its further application. Herein, the Faradaic-based electrode is proposed to overcome the above limitations, offering an ultrahigh adsorption capacity and a rapid removal rate. In this paper, the open framework structure Na3V2(PO4)3@C is applied for the first time as a novel Faradaic electrode in the hybrid capacitive deionization (HCDI) system. During the adsorption and desorption process, sodium ions are intercalated/deintercalated through the crystal structure of Na3V2(PO4)3@C while chloride ions are physically trapped or released by the AC electrode. Different concentrations of feedwater are investigated, and a high SAC of 137.20 mg NaCl g-1 NVP@C and low energy consumption of 2.157 kg-NaCl kWh-1 are observed at a constant voltage of 1.0 V, a concentration of 100 mM, and a flow rate of 15 mL min-1. The outstanding performance of the Na3V2(PO4)3@C Faradaic electrode demonstrates that it is a promising material for desalination and that HCDI offers great future potential.

Coconut shell-derived activated carbon and carbon nanotubes composite: a promising candidate for capacitive deionization electrode

This study presents a sustainable approach for synthesizing high-performance activated carbon from Spirulina Alga through hydrothermal carbonization followed by chemical activation using potassium hydroxide. The resulting activated carbon exhibited a high Brunauer-Emmett-Teller (BET) surface area of 1747 m2/g and a total pore volume of 1.147 cm3/g, with micropore volume accounting for 0.4 cm3/g. Characterization using Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS), X-ray Photoelectron Spectroscopy (XPS), and gas adsorption analyses confirmed the presence of hierarchical micro- and mesoporosity as well as favorable surface functional groups. The synthesized carbon was used to fabricate electrodes for membrane capacitive deionization (MCDI) along with cation and anion-selective membranes, which were then tested with saline water (500-5000 ppm) and synthetic hard water (898 ppm of total salts). The salt adsorption capacity (SAC) reached 25 (batch) to 40 (continuous) mg/g, while rapid adsorption rates with average salt adsorption rates (ASARs) values exceeding 10 (batch) to 30 (continuous) mg·g-1·min-1 during early stages were obtained. Batch MCDI experiments demonstrated a higher SAC compared to continuous operation, with non-monotonic trends in SAC observed as a function of feed concentration. Ion adsorption kinetics were influenced by ion valency, membrane selectivity, and pore structure. The specific energy consumption (SEC) was calculated as 8-21 kJ/mol for batch and 0.1-0.5 kJ/mol for continuous process. These performance metrics are on par with or surpass those reported in the recent literature for similar single-electrode CDI configurations. The results demonstrate the viability of using Alga-derived carbon as an efficient and eco-friendly electrode material for water desalination technologies.

Nanocomposites of α-Fe2O3 (hematite) and (N-doped) graphene oxide (GO) were investigated using first-principles calculations with focus on structure, chemical bonding, electronic structure and H2O adsorption. The nanocomposites were modeled as the interface between the α-Fe2O3 (0 0 0 1) surface and the basal plane of reduced graphene oxide, comprising epoxy groups (C:O ratio of 8) as well as graphitic and pyridinic nitrogen doping. The composite structures exhibited strong chemical bonding by the formation of a bridging Fe–O–C bond. The calculated binding energy between the materials was −0.56 eV per Fe–O–C bond for GO and up to −1.14 eV for N-doped GO, and the binding energies were found to correlate with the charge of the bridging oxide ion. The composites exhibited partly occupied carbon states close to or above the α-Fe2O3 valence band maximum. Dissociative adsorption of H2O was found to be more exothermic for the composites compared to the individual materials, ranging from about −0.9 to −1.7 eV for the most stable configurations with hydroxide species adsorbed to GO and protons forming NH groups or adsorbed to the α-Fe2O3 surface.

Understanding the mechanism of carbonization and KOH activation of polyaniline leading to enhanced electrosorption performance

Studying the electrosorption performance of activated carbon electrodes in batch-mode and single-pass capacitive deionization

Copper hexacyanoferrate/carbon sheet combination with high selectivity and capacity for copper removal by pseudocapacitance

Carbon-based nanomaterials such as graphene, graphene oxide, carbon nanotubes, graphene nanoribbons, etc. are considered as promising materials for energy storage and conversion, electrode sensing, optical and electronic applications. High specific surface area, porosity, and chemical modifications are some of the most important factors for tailoring the (electro)chemical, physical, and mechanical properties of graphene derivatives.1 Nitrogen-doped graphene derivatives have been identified as promising materials for energy storage and conversion2 and sensing applications. One of the most common syntheses of N-doped graphene derivatives is the N-doping of graphene oxide prepared by the Hummers method. The methods for simultaneous N-doping and reduction of graphene oxide are diverse: thermal annealing, pyrolysis, solvothermal, laser ablation, microwave-assisted, and hydrazine treatment.1 However, the above methods yield N-doped graphene derivatives, which are usually poorly exfoliated and have a low specific surface area. Therefore, an efficient strategy to improve the specific surface area of N-doped graphene oxide derivatives needs to be developed.3 Herein we present a new "induction heating method" for the preparation of N-doped reduced graphene oxide derivatives (N-rGOD) with a high specific surface area. N-rGOD was prepared in a two-step process from commercially available graphites (Gs) and multi-walled carbon nanotubes (MWCNTs). In the first step, graphite oxide precursors were synthesized from Gs or MWCNTs by the improved Hummers method. In the second step, the graphite oxide precursors were subjected to rapid heat treatment by induction heating in a reductive ammonia atmosphere. Due to the rapid thermal expansion of graphite oxide, massive exfoliation occurred to obtain N-rGOD with higher specific surface area.4 These materials were tested for energy storage and conversion applications and showed excellent properties. References (1) Xu, H.; Ma, L.; Jin, Z. Nitrogen-Doped Graphene: Synthesis, Characterizations and Energy Applications. J. Energy Chem. 2018, 27 (1), 146–160. https://doi.org/10.1016/j.jechem.2017.12.006.(2) Nosan, M.; Löffler, M.; Jerman, I.; Kolar, M.; Katsounaros, I.; Genorio, B. Understanding the Oxygen Reduction Reaction Activity of Quasi-1D and 2D N-Doped Heat-Treated Graphene Oxide Catalysts with Inherent Metal Impurities. ACS Appl. Energy Mater. 2021. https://doi.org/10.1021/acsaem.1c00026.(3) Alazmi, A.; El Tall, O.; Rasul, S.; Hedhili, M. N.; Patole, S. P.; Costa, P. M. F. J. A Process to Enhance the Specific Surface Area and Capacitance of Hydrothermally Reduced Graphene Oxide. Nanoscale 2016, 8 (41), 17782–17787. https://doi.org/10.1039/c6nr04426c.(4) Qiu, Y.; Guo, F.; Hurt, R.; Külaots, I. Explosive Thermal Reduction of Graphene Oxide-Based Materials: Mechanism and Safety Implications. Carbon N. Y. 2014, 72, 215–223. https://doi.org/10.1016/j.carbon.2014.02.005.

Graphene oxide electrode for unusual water softening in capacitive deionization

The development of high‐performance capacitive deionization (CDI) electrodes demands innovative materials that integrate rapid ion transport, high salt adsorption capacity (SAC), and oxidative stability. This challenge is addressed through a surface nanoarchitectonics strategy, constructing 2D mesochannel polypyrrole/reduced graphene oxide heterostructures (mPPy/rGO) with ordered 1D mesochannels (~8 nm) parallel to the graphene surface. By confining the self‐assembly of cylindrical polymer brushes on freestanding rGO substrates, directional ion highways are simultaneously engineered that significantly reduce transport tortuosity. In addition, corrosion‐resistant polymer interfaces block oxygen penetration, and strong interfacial interactions between PPy and rGO ensure efficient electron transfer. The mPPy/rGO‐based CDI cell achieves breakthrough performance: ultrahigh SAC of 84.1 mg g−1 (4.5× activated carbon, the salt concentration: 2 g L−1), and 96.8% capacity retention over 100 cycles in air‐equilibrated saline solution (the salt concentration: 500 mg L−1). This interfacial confinement methodology establishes a universal paradigm for designing polymer‐based desalination materials with atomically precise transport pathways.

Predicting the salt adsorption capacity of different capacitive deionization electrodes using random forest

Capacitive deionization (CDI) is a low energy desalination technology with long-cycle life, which utilizes high-porosity capacitive electrodes for capturing ions from flowing saline water [1, 2]. Though still suffering from relatively low desalination capacity, one major advantage of CDI technology is its low energy requirement and high rate operation for desalination. In recent years, much effort has been put on improving electrode materials for CDI applications. These studies have mostly focused either on the use of novel electrode materials or on surface modifications (e.g. metal oxide growth, chemical treatment, and thermal treatment) of the existing CDI electrode materials [1, 3, 4]. Although thermal treatment of carbon electrodes for improved charge storage is a well-established approach, the effects of various thermal treatment procedures on the performance of CDI electrodes still remain unexplored. Inherent similarities between the operating principles of supercapacitors and CDI technology might make one to think a similar correlation could be established between thermal treatment and the CDI performance. However, due to major differences in required charge storage mechanisms, a detailed study on various treatment conditions should be conducted to understand which conditions specifically promote better ion adsorption in CDI electrodes. Motivated by this, the effects of different thermal treatment conditions (i.e., temperature and gases) on salt adsorption performances of the activated carbon cloth (ACC) electrodes were investigated. Major discrepancy between stored charge versus salt adsorption capacity (SAC) was observed for different treatment conditions. To better assess these effects, additional BET and Raman tests on the ACC electrodes were also conducted. Results indicated interesting observations regarding charge storage capacity and SAC for different treatment conditions, which highlights the importance of selecting a suitable thermal treatment condition for enhancing the CDI performance of ACC electrodes.

Capacitive deionization (CDI) has been considered a reliable technology used to provide water with low salt concentration and low energy consumption. However, there are still some drawbacks to overcome concerning the choice of the electrode material. Carbon electrodes are extensively used for CDI electrodes since they provide a stable material with high pore volume and good conductivity. However, it is been challenging to find a low-cost symmetric CDI electrode with high salt adsorption capacity (SAC), fast electrosorption kinetics and good energy efficiency. Recently, our group published a paper reporting the use of activated carbon derived from polyaniline (PAC), a low-cost precursor, with high SAC and good electrosorption kinetics. It was demonstrated that the use of different polyaniline (PAni) dopants have a strong influence on the activate carbon properties and, consequently, the electrode performance for CDI. In the present research, it was explored the use of PAC electrodes varying the carbonization temperature before the activation. It was observed a strong dependence of the specific surface area (SSA) and pore size distribution (PSD) on the carbonization temperature. When low temperatures (500 °C) were employed during carbonization (PAC500), the BET SSA was 3653 m²/g and pore volume of 2.50 cm³/g was obtained while at higher carbonization temperatures (850 °C) this value was much lower (2362 m²/g of SSA and 1.26 cm²/g of pore volume for PAC850). The BET SSA obtained in this work is among the highest values reported in literature. The explanation for this high value is probably ascribed to the reactivity of the low temperature carbonized PAni with KOH. Indeed, when PAni was carbonized in temperatures lower than 500 °C all the material was consumed during the activation step, indicating a strong reactivity of the precursor with KOH. These values of SSA and pore volume resulted in an outstanding performance as symmetrical electrodes for CDI. The capacitance of PAC500 and PAC850 measured in a NaCl 0.2 M solution were 213 F/g and 162 F/g, respectively. These impressive values are result of the high SSA and pore volume of PAC materials. Finally, the CDI desalination carried out in batch operation mode also showed an outstanding SAC performance for symmetric electrodes, achieving 22 mg/g for PAC500 and 15 mg/g for PAC850. Moreover, 85% and 76% of electrode saturation was reached after 5 minutes of electrosorption for PAC500 and PAC850, respectively, indicating very fast electrosorption kinetics. This work present a very promising electrode material for CDI and shows how important is the carbonization temperature for PAC electrodes. Figure 1

Enhancing capacitive deionization performance with charged structural polysaccharide electrode binders