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• Activated carbon derived from agriculture by-products obtain high surface area, high porosity, and low density. • Deionization efficiency of CDI, MCDI, and FCDI reached 80–90 % and water recovery rate 90 %. • The roller, spray coating, and mill ball grinding are useful to fabricate electrodes for industry applications. • The adsorption capacities of AC and AC-modified electrodes were 25–40 mg/g. • Life span and deionization efficiency of the flow electrode are higher than electrode plate. Capacitive deionization (CDI), membrane capacitive deionization (MCDI), and flow capacitive deionization (FCDI) are emerging technologies applied to remove ions from brackish water or saline wastewater based on electrode double layer (EDL) mechanisms. The electrode itself can be seen as the most important factor that determines the deionization efficiency of the CDI system. Electrode fabrication using activated carbon derived from agriculture byproducts is a useful solution to decrease cost, restrict environmental pollution, and enable agriculture waste recovery. In this review, the primary parameter's impact on activated carbon (AC) and the electrode fabrication process from the agriculture byproducts is detailed in a discussion to find the most optimal conditions. With excellent characteristics for the activated carbon such as a surface area of up to 2500 m2/g, it can be used to fabricate electrodes that have a high adsorption capacity of approximately 25 mg/g, able to be advanced to 40 mg/g with a modified AC. It can achieve a cycle performance of 95–97 %. The deionization efficiency of the CDI, MCDI, and FCDI systems can be up to 90 % with an input salt concentration from 2000 to 3000 mg/L where the water recovery ratio achieved is 50–90 %, alongside a salt rejection rate of about 7–75 %. AC can be modified to increase its special properties such as surface area, conductivity, and ion selectivity using different methods. The drawbacks and challenges of the CDI technology are also mentioned along with useful solutions such as electrode coating techniques using an anilox roller and a spray, for use in industry applications. [Display omitted] [ABSTRACT FROM AUTHOR]

• Enhanced CuHCF performance due to MWCNTs, improving charge transfer. • Ion selectivity sequence determined: K + > Ca2+ > Na+ > Mg2+. • Voltage control modulates CuHCF@CNT ion selectivity factor. This study utilizes a simple co-precipitation method to synthesize copper hexacyanoferrate (CuHCF) composites reinforced with carbon nanotubes (CNTs) (denoted as CuHCF@CNTs) serving as superior electrode materials for the electrochemical deionization (ECDI) application, a versatile method for brackish water deionization, water softening, and heavy metal removal. The enhanced performance of CuHCF, one of the Prussian blue analogues (PBAs) with typical Faradaic cation-capturing capability, is attributed to the increased charge transfer and a large surface area provided by multi-wall carbon nanotubes (MWCNTs) for the promoting the utilization of CuHCF units within the composites. The ion selectivity of electrode materials is investigated using both batch and microfluidic reactors, revealing a selectivity sequence of K + > Ca2+ > Na+ > Mg2+. Additionally, this study introduces a novel approach for controlling the ion selectivity of CuHCF@CNT from the operating voltage. By varying the cell voltage, the selectivity factor, β K/Mg , can be increased from 1.7 at 1.2 V to 4.5 at 0.6 V. Our research offers a new perspective on the ion-capturing selectivity of ECDI systems using Faradaic materials in deionization and ion-concentrating applications. [ABSTRACT FROM AUTHOR]

• Different carbon-based electrodes following a nature-inspired solution were tested by CV and EIS. • Glass-carbon electrodes (GCE) and carbon paper-based electrodes (CPE) with and without polytetrafluoroethylene (PTFE) were evaluated. • The electrodes' performance was assessed by employing the ferri/ferrocyanide ([Fe(CN) 6 ]3-/4−) electrochemical probe. • Surface properties of the commercial electrodes materials were evidenced from AFM and water contact angle measurements. • Best results were achieved with CPE without PTFE, given its hierarchical porous structure and absence of the insulating binder. Carbon electrodes are widely accepted as very versatile platforms, with applications ranging from electrocatalysis to sensors and other devices, like fuel cells and water electrolyzers. However, there are still difficulties given that over time, at high potentials, the oxidation of carbon materials (as a catalyst and/or catalyst support) can play a detrimental role, undermining the efficiency and stability of the electrochemical processes and devices performance. In this paper, it is reported the research work followed by resourcing to electrochemical analytical techniques, like cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), along with complementary atomic force microscopy (AFM) and water contact angle (WCA) measurements. These techniques were used to characterise glass-type and paper-based carbon electrodes. On a nature-inspired solution, we took advantage of the different interfacial carbon-support hierarchical porous structures to boost the carbon electrocatalytic effect towards sensing the ferri/ferrocyanide redox couple ([Fe(CN) 6 ]3-/4−) in aqueous solution. It is shown that the best results were achieved with carbon paper electrodes without wet proofing, given its hierarchical porous structure and absence of the insulating binder. This research endeavors to contribute to the ongoing advancements in the field of electrochemical green energy conversion by exploring innovative approaches and materials, with the ultimate aim of developing carbon substrates that not only enhance performance but also promote environmental sustainability. [Display omitted] [ABSTRACT FROM AUTHOR]

Capacitive Deionization (CDI) technology achieves ion immobilization through a reversible electrochemical process, gradually emerging as a substitute for conventional desalination techniques due to its simplicity, efficiency, and energy-saving advantages. Materials design has played a pivotal role in the continuous refinement and development of the CDI theoretical framework, with substantial efforts directed towards the design of high-performance novel electrode materials. Among them, Covalent Organic Frameworks (COFs) have been explored as exceptionally promising candidates. COFs represent a burgeoning class of porous crystalline materials, characterized by pronounced intrinsic features encompassing high tunability, highly ordered pore structures, elevated surface areas, and an abundance of functional sites. Consequently, it becomes more facile to tailor channels with facile ion transport and immobilization, facilitating the seamless integration of ion-selective electrochemical redox-active sites. This ultimately fulfills the design objectives for CDI materials. This comprehensive review aims to systematically and comprehensively explore the underlying design fundamentals, principles and frontiers of COFs materials for CDI. Specifically, discussions encompass the three major research challenges of enhancing intrinsic conductivity, suppressing co-ion effects and Faradaic side reactions, and delving into mechanistic studies. These insights provide valuable guidance for the future design of sustainable, high-performance, and ion-selective capacitive deionization electrode materials. [ABSTRACT FROM AUTHOR]

• NASICON-type Na 3 (VO) 2 (PO 4) 2 F is used as cathode material for AZIBs. • Na 3 (VO) 2 (PO 4) 2 F@CNT cathode material exhibits a high specific capacity of 143 mAh‧g−1 at 0.2 C • Na 3 (VO) 2 (PO 4) 2 F@CNT shows a good low-temperature electrochemical performance. • The electrochemiscal reaction mechanism is studied by ex-situ XRD and XPS. Aqueous zinc-ion batteries (AZIBs) are one of the candidate technologies for large-scale energy storage systems due to their environmental friendliness, safety and resourcefulness. However, designing and synthesizing high-performance cathode materials with practical application value is currently a great challenge. Herein, we synthesize a carbon-nanotube-coated Na 3 (VO) 2 (PO 4) 2 F (Na 3 (VO) 2 (PO 4) 2 F@CNT) cathode material for AZIBs, which has a continuous and interconnected ion transport channel structure. A Zn2+/H+ co-intercalation mechanism is revealed by ex-situ X-ray diffraction (XRD) and ex-situ X-ray photoelectron spectroscopy (XPS) characterizations. The Na 3 (VO) 2 (PO 4) 2 F@CNT cathode material exhibits a high specific capacity of 143 mAh‧g Wan et al. (2019). at 0.2 C in the electrolyte of 3 M Zn(OTf) 2 aqueous solution. In addition, Na 3 (VO) 2 (PO 4) 2 F@CNT shows a good low-temperature electrochemical performance in the electrolyte of 2 M Zn(OTf) 2 deionized water/ethylene glycol (DIW/EG) mixed solution with a different ion storage mechanism. This study provides a new polyanionic cathode material for AZIBs and an idea to modulate the electrolyte polarity to enhance the zinc storage capacity of the cathode material. [Display omitted] [ABSTRACT FROM AUTHOR]

NASICON structure type materials are attracting increasing attention as electrode active materials for ion insertion batteries and deionization devices. NaTi 2 (PO 4) 3 due to its favorable potential is among the most suitable negative electrodes for various applications in aqueous electrolytes. However, various parasitic processes limit its Coulombic efficiency, self-discharge characteristics, and capacity retention. Understanding and mitigation of these processes are essential in order to fully utilize the potential of such and similar materials. In this study, the degradation mechanisms of NaTi 2 (PO 4) 3 in aqueous electrolytes is studied in great detail. The results indicate that, to a different extent, both hydrogen evolution and oxygen reduction reactions are taking place during NaTi 2 (PO 4) 3 electrochemical cycling and contribute to pH increase. The latter reaction due to the presence of Ti(III) species is found to be prevalent in aerated electrolytes. There is virtually no degradation and capacity loss observed at pH 7, but it becomes significant at pH 10 even in oxygen-free electrolytes. Contrary to previous studies, this work shows that capacity loss is actually slower at lower C-rates. The post mortem X-ray diffraction analysis shows that only a fraction of capacity loss could be directly attributed to NaTi 2 (PO 4) 3 decomposition and even less to its dissolution into electrolyte. Therefore, most of the observed capacity fade during cycling is related to contact loss in the electrode structure which most likely comes from the formation of electron blocking aqueous interphasial layer. [ABSTRACT FROM AUTHOR]

The influence of surface chemistry on heterogeneous electron transfer at activated carbon (AC) electrodes was studied using scanning electrochemical microscopy (SECM) and conventional electrochemical measurements, which allow for measuring respectively the local and the overall electrode electron transfer rate constants. Using a thermal treatment in air and under argon, commercial activated carbons were either oxidized or defunctionalized. Both treatments lead to a slight decrease of the specific surface area of the material, without altering its pore size distribution and morphology. The nanogap voltammetry and approach curves obtained by SECM were used to characterize the rate constants at the interface between an aqueous solution of ferrocenemethanol (FcMeOH) and the AC electrodes. The heterogeneous electron transfer (HET) rate constant for the untreated AC was 3.4 10−2 ± 0.2 cm s−1 and was increased by about 2.5 and 1.5 times, after oxidizing and defunctionalizing the surface, respectively. SECM results showed that the heat treatment increases the conductivity of AC, and the oxidation of the surface increases the wettability and accessibility of the pores, which are assumed to promote the electron transfer. The local heterogeneous electron transfer rate constant values obtained by SECM are higher, by an order of magnitude, than the global ones obtained from conventional electrochemical macroelectrode measurements. The local information obtained by SECM is valuable for understanding the nanoscale interfacial mechanisms in porous carbon electrodes as a better understanding of the charge storage mechanism is key to improve their electrochemical performances. [Display omitted] [ABSTRACT FROM AUTHOR]

Hydrogen production is an immediate need to replace the fossil fuels to keep environmental balance, and water splitting is an effective solution in presence of catalyst through oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Herein, for the first time, we have synthesized Iron Phosphate Hydroxide (Fe 2.95 (PO 4) 2 (OH) 2) thin film electrode as a superior electrocatalyst by facile hydrothermal method using binder free approach. The crystallographic properties are studied from X-ray diffraction pattern, and Reitveld refinement analysis shows best fit with the tetragonal Lipscombite structure of Iron Phosphate Hydroxide (Fe 2.95 (PO 4) 2 (OH) 2). Flower like structure consist of agglomerated nanorods on micro and sub-micrometric spheres of Fe 2.95 (PO 4) 2 (OH) 2 exhibits lower overpotential of 281 mV at 10 mA/cm2 current density towards OER in alkaline (1 M KOH) medium and maintains its activity after 12 h catalytic stability test. Moreover, prepared electrode shows HER with overpotential 165.7 mV at current density 10 mA/cm2 in acidic (1 M H 3 PO 4) medium and demonstrates enhanced performance (126.4 mV overpotential) after 12 h catalytic stability. The Fe 2.95 (PO 4) 2 (OH) 2 thin film electrodes show superior performance in OER and HER, compared with its oxide counterpart (Fe 2 O 3). Image 1 [ABSTRACT FROM AUTHOR]

Electrodialysis (ED) is a well-established water desalination technology, applied mainly to brackish water desalination. In ED, desalination is driven by an applied electric field, which results in salt ion electromigration through alternating cation and anion exchange membranes. Recently, classical ED cells have been modified by driving them via spontaneous redox reactions occurring at the electrodes. Such a cell is distinct from classical ED as it does not require electricity, but rather requires solely chemical energy input in the form of redox active chemicals, and outputs both desalted water and electricity simultaneously. We here extend ED theory in order to capture a cell driven by spontaneous redox half-reactions occurring at electrode surfaces. In the cell considered, an AEM and CEM are separated by a channel with flowing feedwater. On the opposite side of the AEM is an anode and flowing anolyte, while a cathode and flowing catholyte are on the opposite side of the CEM. To capture cell behavior and performance at steady state, we solve a set of equations comprising the species' Nernst–Planck equation and electroneutrality, which are coupled to activation and concentration overpotential losses at planar electrodes. Our model captures the crossover of coion species through membranes as well as electric potential, counterion, and coion concentration variations within the membranes. We elucidate key predicted phenomena, including that the cell current is limited by reactant starvation at the cathode, and that current and certain ion fluxes scale as x −1/3, where x is the coordinate in the direction of flow. Our model predicts that at steady state, the cell can achieve an order of magnitude reduction in the NaCl concentration of a 500 mM feed, while generating up to ∼42 mW/cm2 electrical power density. Further, we determined that the main limitation of the cell as designed is a relatively high coion crossover flux through the membranes. [ABSTRACT FROM AUTHOR]

Contamination of the ground water with fluoride is a great problem worldwide. Removal of fluoride (F−) ions from simulated natural waters containing fluoride by electrocoagulation (EC) using aluminum electrodes, has been investigated in a discontinuous lab cell. Two types of water have been studied: local tap water and deionized water-based luoride solutions of sodium fluoride with addition of sodium chloride to reach the desired conductivity. The effect of four operating parameters has been followed for a current density fixed at 5 mA/cm2 within the following ranges: fluoride concentration (5–50 mg/L), temperature (25–55 °C), conductivity (1–6 mS/cm) and initial pH (4–8.5). In accordance with published data, the presence of 61 mg/L buffering hydrogencarbonate ions in the tap water was found to substantially reduce the Al(III) amount required for a given abatement in comparison with deionized water. Performance comparison of the discontinuous electrocoagulation treatment between the two types of water has been discussed for 90% abatement of F− introduced, in terms of the amount of Al(III) dissolved over the initial fluoride concentration, the parameters of a previous adsorption model and the fraction of Al(III) flocs not involved in the adsorption. EC performances were shown to be governed by the solution pH for the two types of water, with little effect of the other operating conditions: at initial pH 6, F− abatement was found to require two or three times less trivalent aluminium than at initial pH 8.5. • Fluoride ions can be removed efficiently from water by electrocoagulation. • Lower aluminium amounts are required with hydrogencarbonate anions. • Temperature, concentration and conductivity impact on the treatment performance. • In any condition, more efficient treatment is obtained with pH lower than 7.5. [ABSTRACT FROM AUTHOR]

Novel two-dimensional carbon nitride hexagonal-like sheets were fabricated from thermal condensation, which uses hexaazatriphenylene-based precursor prepared microporous and oxidation resistant carbons materials (HAT-CN). The results show that the as-prepared HAT-CN is the first electrode utilized in capacitive deionization, due to the rich heteroatom and border-group content, as well as the potential collaborative effect of C and N atoms, displaying the quick ion diffusion and strong charge transfer performance. Additionally, the capacitive deionization performance of HAT-CN is improved by the synergistic contribution of a large accessible surface area, large pore volume, and high graphitization. The electrode of HAT-CN was carbonized at 550 °C which display an excellent specific capacitance of 179.2 F g−1 in 1-M NaCl solution at a scan rate of 5 mV s−1. Subsequently, a high salt adsorption capacity of 24.66 mg g−1 was attained for an applied voltage of 1.2 V in 500 mg L−1 NaCl solution, showing good cyclic stability at 30 cycles. Considering those excellent properties of the prepared HAT-CN, the capacitive deionization electrode should be an ideal candidate for high-performance deionization application. [ABSTRACT FROM AUTHOR]

As the global demand for potassium continues to increase, the potassium in natural resources is gradually insufficient. The potassium resources in the ocean are extremely rich. In this paper, a new battery deionization method (BDI) was developed to selectively recover potassium from seawater using a Fe[Fe(CN) 6 ] (BG) battery electrode. The BG-based electrode exhibited totally different insertion behavior to the most abundant cations in seawater, with the capacity order of K+>Na+>Li+>Ca2+>Mg2+. Using the battery cell assembled with BG and activated carbon electrode, the recovery capacity of K+ arrived at 177 μmoL/g under the discharge stage of battery from 0.8 to 0 V, and no significant variation was found even in the presence of 37 times higher concentration of Na+ than that of K+. In synthetic seawater, the BG battery electrode still kept the recovery of 69.6% for K+ with the separation factor α(K+/Na+) of 141.7. Moreover, energy consumption is calculated to be 15.4 kJ/mol, 10 times lower than that of the capacitive deionization method. Meanwhile, the BG battery electrode is very stable with the adsorption amount retaining 86% over 150 cycles. The three-cell stack test in synthetic seawater proves that the current BDI device is easy to be amplified for recovering potassium from seawater. Image 1 • K+ recovery by Berlin green battery deionization is demonstrated. • High separation factor α(K+/Na+) of 141.7 is achieved in synthetic seawater. • The recovery of K+ in synthetic seawater arrives at near 70%. • The energy consumption of the battery system is quite low. • The recovery can be improved by increasing battery stack. [ABSTRACT FROM AUTHOR]

Abstract The rational design and synthesis of an efficient bielectrocatalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) by tuning the chemical composition, structure and the catalytic sites of the hybrid materials is always of a great challenge. In this work, an innovative strategy based on the highly active N,N′-carbonyldiimidazole (CDI) is described to one-pot synthesis of a novel precursor for bifunctional O 2- electrocatalyst. The coordination of Co2+ with the in situ generated ligands imidazole and carbonate results in ultrafine cobalt carbonate (CoCO 3)-involved cobalt-based zeolitic imidazole framework (CoCO 3 /Co-ZIF). Owing to the presence of ultrafine CoCO 3 , carbonization of CoCO 3 /Co-ZIF at 800 °C under N 2 atmosphere endows the pyrolysis product with a special skeleton of carbon nanotube (CNT)-tipped end CoO x , multivalent CoO x wrapped in graphitic carbon layers. Thus, the resulting CoO x /Co-N-C exhibits the enhanced and durable ORR/OER performance in alkaline media, due to the fast electron and mass transfers. For ORR, a large limiting current density of 4.59 mA cm−2 can be obtained by CoOx/Co-N-C, which is comparable to that of Pt/C. For OER, it only needs an over potential of 1.65 V to achieve a current density of 10 mA cm−2, merely 30 mV behind IrO 2 (1.62 V). [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) has been used to remove salt ions with carbon electrodes by the electrical double layer (EDL) mechanism. Other non-carbon materials based on pseudocapacitive mechanism resulting from faradaic reactions with fast electrosorption/desorption properties have emerged as new promising electrode materials. Until now, pseudocapacitive behavior was limited to thin film electrodes with nanometer thickness and was not yet suitable for practical application. In this work, we employed a two-times of hydrothermal synthesis process constructing MnFe 2 O 4 /Porous rGO (MFO/PrGO) nanostructure as pseudocapacitive electrodes. In this carefully designed architecture, the dense structure of MFO/rGO prepared by first-time hydrothermal process provided good connections of MFO nanoparticle with rGO framework for efficient redox charge transfer; the chemically-etched porous rGO used in the second-time hydrothermal process offered hierarchical pores for easier access of the electrode materials, both contributed in enhanced pseudocapacitive electrosorption. HRTEM verified the MnFe 2 O 4 spinel structure and measured the inter-planar lattice parameter which functioned for ion intercalating in and out of the electrode. The MFO/PrGO electrode resulted in 237 F/g in electrosorption of ions from aqueous solution which was higher than the MFO only electrode. Finally, in the CDI experiment, the great salt electrosorption capacity of 8.9 mg/g and 100% regeneration in multiple cycles were achieved by the MFO/PrGO nanocomposite electrode. These results paved the way for using spinel compounds and graphene nanocomposite electrodes for efficient electrosorption and desalination. [ABSTRACT FROM AUTHOR]

Abstract In capacitive deionization (CDI) systems, more Faradaic reactions generally occur at a higher cell voltage, resulting in the poor ion-removal efficiency and high energy consumption, but a low cell voltage may lead to a low deionization capacity. In this study, an integrated strategy, consisting of (1) selecting the acceptable charge/discharge time ratio, (2) finding the potential windows of both positive and negative electrodes, and (3) using the charge-balanced method for determining the optimal mass ratio between the positive and negative electrodes (denoted as (m+)/(m−)), is proposed to find the optimal cell voltage of a CDI system with a high desalination efficiency and low energy consumption. According to this strategy, two newly designed cells using two types of activated carbon (AC) show excellent CDI performances; cell 1 with AC = ACS679, (m+)/(m−) = 1:1.4, and cell voltage = 1.4 V: salt adsorption capacity of 12 mg g−1, charge efficiency of 62%, and energy consumption of 109 kJ mol−1 and cell 2 with AC = ACS25, (m+)/(m−) = 1:1, and cell voltage = 1.2 V: salt adsorption capacity of 13 mg g−1, charge efficiency of 81%, and energy consumption of 72 kJ mol−1 although the potential window of water decomposition for such AC-coated electrodes in 8 mM NaCl is about 2 V. This universal strategy is applicable to all CDI systems utilizing various electrode materials. Graphical abstract Image 1 Highlights • We demonstrate a universal strategy for constructing the AC//AC cell with high CDI performances. • The same charge/discharge time ratio with high reversibility on both electrodes is the key. • Influences of two-electrode mass ratio on the desalination performances are studied. • The pH change is affected by the Faradaic reactions from the potential windows of electrodes. [ABSTRACT FROM AUTHOR]

Abstract Clofibric acid (CA) is a ubiquitous pollutant that is resistant to traditional wastewater treatments. Here, photoelectrocatalytic (PEC) degradation of CA using a FeOOH/P:BiVO 4 /rGO photoanode is investigated. The characteristics by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) on the electrode-electrolyte interface were performed to optimize different electrolyte conditions (Na 2 SO 4 concentration, CA concentration, and pH). EIS is found to be a simple, fast method to study the electrolyte conditions for PEC decomposition of CA on BiVO 4 composites electrodes. The experimental results demonstrated that the electrolyte conditions had an effect on the surface coverage of V5+/V4+ redox species and surface states related to ion/molecule distribution on the electrode surface. The optimum deposition time was 6 min. And the optimum electrolyte conditions were as follows: the concentration of Na 2 SO 4 was 0.2 mol L−1, the concentration of clofibric acid was 5 mg L−1, and pH was 7. Under these conditions, FeOOH/P:BiVO 4 /rGO photoanode showed a removal rate of CA 96% in 6 h under visible light irradiation (λ ≥ 420 nm). It also showed a good photoelectric stability. FeOOH/P:BiVO 4 /rGO photoanode showed a potential application in the photoelectrochemical degradation of CA. Graphical abstract Image 1 Highlights • A simple and fast way to optimize the optimum degradation conditions by impedance spectroscopy. • The FeOOH/P:BiVO 4 /rGO exhibits much improved photoelectrochemical activity. • The photoanode efficient removal efficiencies for clofibric acid. • A plausible PEC degradation clofibric acid mechanism was proposed. [ABSTRACT FROM AUTHOR]

Abstract In this study, the method of hydrothermal synthesis is introduced to prepare the titanium dioxide (i.e.,TiO 2) tetragonal prism array on the conducting plane of fluorine-doped tin oxide (i.e., FTO), and then the polyaniline (i.e., PANI) is coated on the surface of TiO 2 array by normal chemical oxidation to form the PANI/TiO 2 shell/core nanoarray. The array architecture of PANI/TiO 2 composite is further confirmed by SEM, XPS, XRD, UV–vis and Raman spectroscopy. The regular array structure of PANI/TiO 2 can reduce the resistance of ionic diffuse and charge transfer via optimizing the ionic diffusion to obtain a lower impedance and higher specific capacitance. Compared with the individual component (PANI or TiO 2), the PANI/TiO 2 /FTO electrode possesses a higher specific capacitance as the supercapacitor electrode material. The maximum specific capacitances of 633 F/g at the rate of 10 mV/s and 781 F/g at the current density of 1 A/g are obtained in the PANI/TiO 2 /FTO electrode and it is superior or close to individual PANI or PANI-based materials. In addition, the TiO 2 array can undertake some mechanical deformation in the redox process without destroying the electrode material to enhance the cyclic stability of PANI/TiO 2 /FTO electrode. The capacitance retention of PANI/TiO 2 /FTO electrode keeps 75% of its initial value which is higher than that of the PANI/FTO electrode (65%) after 2000 cycles. Therefore, such array architecture composite can be promisingly used as the electrode material for electrochemical capacitive energy storage. Graphical abstract The array architecture of PANI/TiO 2 shell/core composite was successful prepared onto the conducting plane of ITO. The PANI/TiO 2 shell/core array can reduce the resistance of ionic diffuse and charge transfer via optimizing the ionic diffusion to obtain lower impedance and a higher specific capacitance. The maximum specific capacitance of 633 F/g at rate of 10 mV/s and 781 F/g at 1 A/g are obtained in the PAN/TiO 2 /FTO electrode and it is superior or close to individual PANI or PANI-based materials. Image 10723 Highlights • The PANI/TiO 2 shell/core array was successful prepared onto the conducting plane of the ITO. • The specific capacitance of 781 F/g was obtained when PANI/TiO 2 acted as the electrode. • The cycling stability with capacitance retentions of 75% after 2000 cycles. • The PAN/TiO 2 shell/core array can reduce the resistance of ionic diffuse and charge transfer. [ABSTRACT FROM AUTHOR]

Abstract Electrochemical oxidation is an effective mean to degrade non-biodegradable organics from the contaminated waters. However, its current efficiency is very low for the low-concentration organic pollutants treatment. In this work, combining with the outstanding adsorption property of CNT and the effective electrocatalytic oxidation performance of β-PbO 2 , we constructed novel layer-by-layer carbon nanotube/PbO 2 anodes (CNT/PbO 2 -3, CNT/PbO 2 -4 and CNT/PbO 2 -5) with high adsorbability to enhance the electrochemical degradation efficiency of low-concentration sodium pentachlorophenate (PCP Na). In electrochemical oxidation tests, the PCP-Na was rapidly enriched in the CNT/PbO 2 film through adsorption/electrosorption and then efficiently degraded in site. The removal efficiency of low-concentration PCP-Na (5 mg/L) on CNT/PbO 2 -4 reached 73.8% after only 5 min of electrolysis, whereas that on pure PbO 2 was only 9.9%. To further clarify the mechanism of improvement of PCP-Na removal on CNT/PbO 2 -4 anode, the generation capacity of·OH radicals, oxygen evolution overpotential, voltammetric charge quantity, interface resistance, and specific surface area of CNT/PbO 2 -4 anode were also assessed and compared with those of other three anodes. Results showed that, in addition to the synergistic effect of adsorption/electrosorption and electrocatalysis, the more active sites, smaller electron transfer resistance and higher direct oxidation capacity of CNT/PbO 2 -4 anode also contributed to improving degradation rate of PCP-Na on CNT/PbO 2 -4 anode. Additionally the electrochemical degradation pathway of PCP-Na was also proposed based on the gas chromatography-mass spectrometry analysis. Finally, CNT/PbO 2 -4 electrode exhibited longer accelerated lifetime of 116 h than pure PbO 2 electrode (91 h). Thus, these findings provide a new anode to improve the removal of low-concentration organic pollutants through combining electrochemical oxidation and adsorption/electrosorption processes. Graphical abstract Image 1 Highlights • A novel layer-by-layer CNT/PbO 2 anode was fabricated. • The degradation efficiency of PCP-Na on CNT/PbO 2 anode was obviously improved. • The low-concentration PCP-Na was enriched on the surface CNT/PbO 2 anode. • Adsorption/electrosorption and electrocatalysis were combined. [ABSTRACT FROM AUTHOR]

Abstract Carbon Xerogel electrodes' materials were prepared by polycondensation of resorcinol and formaldehyde. They show accommodation of anions in preference to cations by their porous structure. In addition, their selectivity toward anion electroadsorption was found to be pH dependent, with an increase in electrodes' capacitance in acidic solutions. This dependence of the capacitance on the pH of the solution is explained by the presence of functional carboxylic surface groups in the Xerogel carbon micropores, determined by Boehm titration to be 3.26 meq/g. These functional surface groups give rise to the Donnan exclusion effect, whereby they cause partial repulsion of anions from the microporous structure. When the pH of the electrolyte solution is acidic (<2), most of these acidic functional surface groups are in their non-ionized state, and hence anions can freely penetrate the Xerogel carbon microporous structure. The pH dependent capacitance of these carbons was utilized to examine the feasibility of energy extraction from mixing of saline and acidic solutions following the four basic steps of capacitive mixing processes – charge, solution exchange, discharge, and another solution exchange. As opposed to what we expected, a potential rise was observed when the solution was exchanged from acidic to saline, rather than during the other exchange, from saline to acidic solution. It appears that upon exchange of the solutions from saline to acidic, the expected potential rise resulting from the change in the electrodes capacitance, is cancelled by the new quinone-hydroquinone equilibrium that is established on the electrodes by their surface groups. The ability of these surface redox functional groups to store charge provides a basis for energy extraction from the neutralization of acidic solutions, as described herein. [ABSTRACT FROM AUTHOR]

Abstract A simple strategy which combines the treatment of industrial wastewater with the preparation of electrode materials was proposed in this work. And the industrial wastewater is the only iron source for the material preparation. The preparation method in this work is facile, economical and environment-friendly which includes two simple steps of low-temperature aqueous solution and one-step calcination. Moreover two kinds of high performance Fe 2 O 3 anode materials (α-/γ-Fe 2 O 3 nano spheres, respectively) with isomerism can be obtained by simply adjusting calcination temperatures. Both of the α-Fe 2 O 3 and γ-Fe 2 O 3 nanospheres show good lithium storing reversibility when used as anode materials in LIBs. Furthermore the as-prepared α-Fe 2 O 3 nano-electrode with lower electrochemical impedance exhibit a far better electrochemical performance (about 74.1% capacity retention (calculated based on the lithiation) from the 1st to 5th cycle) than the γ-one (only 39.0% capacity retention from the 1st to 5th cycle). The results here provide economical yet environment-friendly strategies for developing advanced anode material demanding both high energy and long lifespan for full-cell lithium battery. Highlights • Waste utilization and material preparation are effectively combined in this paper. • The industrial wastewater is the only iron source for the material preparation. • Isomeric Fe 2 O 3 anode materials can be obtained by simply adjusting calcination temperature. • The α-Fe 2 O 3 electrode exhibits a relatively high and stable reversible capacity. [ABSTRACT FROM AUTHOR]

Abstract Metal–organic frameworks (MOFs), which combine organic and inorganic components, are promising materials for energy storage. The conjugated structure of MOFs offers excellent electrical conductivity and charge storage performance. In this study, we introduce Zn-p–phenylenediamine (Zn-pPDA) MOFs for a first time in energy storage devices, and we also use a green and facile synthesis method for the preparation of the materials. Multi-layered Zn-pPDA MOF nanostructures with a thickness of 1–5 μm and a width of ∼20 nm are synthesised using liquid–liquid interfacial reactions. Their MOF complexes are used to fabricate positive electrodes for supercapacitors. The MOF supercapacitors exhibit high energy and power densities of approximately 62.8 Wh/kg and 4500 W/kg, respectively. Additionally, excellent cyclability with ∼96% capacitive retention after 2000 cycles is obtained. We show that the synthesis method can open a new pathway for formulating pPDA-ligand-based MOFs, and that the Zn-pPDA MOF is a highly promising material for future energy storage devices. [ABSTRACT FROM AUTHOR]

Abstract Major challenges for effective implementation of the Electro-Fenton (EF) water treatment process are that conventional efficient cathodes are relatively expensive, and H 2 O 2 activation by Fe2+ may cause secondary pollution. Herein, we propose a low-cost activated carbon/stainless steel mesh (ACSS) composite cathode, where the SS mesh distributes the current and the AC simultaneously supports H 2 O 2 electrogeneration, H 2 O 2 activation, and organic compounds (OCs) adsorption. The oxygen-containing groups on the AC function as oxygen reduction reaction (ORR) sites for H 2 O 2 electrogeneration; while the porous configuration supply sufficient reactive surface area for ORR. 8.9 mg/L H 2 O 2 was obtained with 1.5 g AC at 100 mA under neutral pH without external O 2 supply. The ACSS electrode is also effective for H 2 O 2 activation to generate OH, especially under neutral pH. Adsorption shows limited influence on both H 2 O 2 electrogeneration and activation. The iron-free EF process enabled by the ACSS cathode is effective for reactive blue 19 (RB19) degradation. 61.5% RB19 was removed after 90 min and 74.3% TOC was removed after 720 min. Moreover, long-term stability test proved its relatively stable performance. Thus, the ACSS electrode configuration is promising for practical and cost-effective EF process for transformation of OCs in water. Graphical abstract Image 1 Highlights • A novel iron-free Electro-Fenton process is proposed for oxidation of chemicals in water. • A low-cost granular activated carbon/stainless steel mesh electrode is used for the process. • Effect of electrolyte pH and current on H 2 O 2 production are investigated. • Neutral pH could supported effective H 2 O 2 electrogeneration and H 2 O 2 activation. • Long-term stability for H 2 O 2 production, H 2 O 2 activation, OH production is verified. [ABSTRACT FROM AUTHOR]

Abstract Covalent triazine-based frameworks (CTFs) with high nitrogen content, porous structures and low electric resistance were synthesized and applied as membrane capacitive deionization (CDI) electrodes for the first time. The obtained CTFs exhibit abundant micropore structure which provide adsorption site for ion and certain hydrophilicity ensure the whole pore volume is participating. The electrodes of p -CTFs show ideal capacitive behavior with the maximum specific capacitance values of 122.63 F g−1 at a scan rate of 1 mV s−1 under 1 M NaCl solution. Besides, the further membrane capacitive deionization by batch mode experiment exhibits excellent electrosorption capacity of 29.34 mg g−1 under 1.2 V in a 1000 mg L−1 NaCl solution and stable regeneration performance. With the admirable properties mentioned above, the prepared CTFs can offer great opportunities as promising CDI electrodes for application of high-performance desalination. [ABSTRACT FROM AUTHOR]

Abstract In this work, we report the use of pseudocapacitive RuO 2 in a porous carbon-based substrate as a composite electrode for high-performance capacitive deionization (CDI). RuO 2 was electrodeposited onto inexpensive activated carbon (AC) via cyclic voltammetry to optimize the composite electrode (denoted as RuO 2 (20)-AC) fabrication. The electrochemical measurements indicate that the composite electrode with a specific surface area of 576 m2/g and hydrophilicity yields an improved specific capacitance and good cycling stability. The notably enhanced performance is attributed to the presence of RuO 2 , which allows rapid Faradaic charge-transfer reactions as well as pseudocapacitive charge storage. These results confirm that incorporating RuO 2 onto an AC electrode effectively reduces the electrical resistance and enhances the charge efficiency. Furthermore, batch-mode CDI experiments were conducted at 1.2 V in a 5 mM NaCl solution. As evidenced, the RuO 2 (20)-AC composite has a promising salt adsorption capacity of 11.26 mg/g, which is 3.7-fold higher than that of pristine AC. Therefore, using the RuO 2 (20)-AC composite as the cathode, an enhanced desalination performance can be achieved through a mixed capacitive-Faradaic process, resulting from two removal mechanisms of capacitive electrosorption and pseudocapacitive redox reactions. This work provides an efficient strategy to utilize RuO 2 on porous carbon-based substrates to improve CDI performance. Highlights • RuO 2 /activated carbon composite electrodes were prepared for CDI. • Electrodeposited RuO 2 showed good pseudocapacitive charge storage. • The metallic conductivity of RuO 2 ensures rapid ion transport. • The composite had a superior salt electrosorption capacity. • The combination of capacitive electrosorption and Faradaic reactions enhanced the CDI performance. [ABSTRACT FROM AUTHOR]

Abstract Development of high-performance electrocatalysts for overall water splitting is vital for the production of renewable hydrogen energy. Monolithic Ni(OH) 2 nanosheets are fabricated through a facile hydrothermal oxidation procedure of commercial Ni foam. And Ni 2 P, Ni 2 S 3 and NiSe 2 nanosheets are obtained by subsequent low-temperature phosphorization, sulfurization and selenization of the monolithic Ni(OH) 2 nanosheets, respectively. The resultant monolithic materials can be directly employed as self-supported electrodes for efficient oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline media, especially, Ni(OH) 2 nanosheets for OER and Ni 2 P nanosheets for HER, respectively, revealing their versatile and practical nature for hydrogen production. Moreover, a well water electrolyzer through a matched electrode pair with Ni(OH) 2 nanosheets as anode and Ni 2 P nanosheets as cathode can achieve a water splitting current density of 10 mA cm−2 at a cell voltage of 1.64 V, and maintains this current density as least 48 h without evident decay in 1.0 mol L−1 KOH electrolyte. These efficient electrocatalysts with a low-cost, facile synthesis procedure and additive-free properties have great potential for emerging realistic energy storage and conversion fields. Graphical abstract A facile strategy was developed for the fabrication of monolithic Ni x M y (M = OH, P, S, Se) nanosheets on Ni foam with integrated configuration. The resultant materials as self-supported electrodes exhibit significant activity and durability for efficient oxygen/hydrogen evolution reactions. Image 1 [ABSTRACT FROM AUTHOR]

Abstract A biomass-derived activated carbon with a systematic control over the pore size distribution is used to decode the effect of pore size distribution on charge dynamics in organic acetonitrile-based supercapacitors. Distinct trends in the high-current capacitance of the positive and negative electrodes are revealed by isolating the ion-specific accessible pore width and specific surface area from the total values calculated on the basis of low-temperature nitrogen adsorption/desorption isotherms. A size match between ions and pores for each separate electrode is established to maximize gravimetric capacitance under high current load. Most importantly, the high-current gravimetric capacitance demonstrates the existence of an optimum micropore width depending on polarization as well as no need for wide micropores or mesopores for ensuring rapid capacitive response. [ABSTRACT FROM AUTHOR]

Abstract The carbon material derived from citrus peel was prepared via hydrothermal synthesis method with low amount of ZnCl 2. The morphology and surface structure of the synthesized carbons were characterized by field emission scanning electron microscope (FESEM), X-ray diffraction (XRD) and N 2 adsorption/desorption isotherms measurements. The electrochemical and capacitive deionization performance of carbon materials were comparatively studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge (GCD). Compared with the materials activated with KOH or H 3 PO 4 , ZnCl 2 -activated carbon showed the best electrochemical double-layer characteristics, with the specific capacity of 120 F g−1. When being applied as anode in the capacitive deionization (CDI) cell, the desalination amount of 16 mg g−1 and the average salt adsorption rate (ASAR) of 0.67 mg g−1 min−1 were achieved, which is much higher than those of KOH- and H 3 PO 4 -activated materials. The desalination amount retained 80% after 35 cycles. The possible mechanism is proposed in light of X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) analysis. This work provides a facile and environmentally friendly method for the preparation of a green and low cost biomass derived porous carbon material by fruit waste with a low amount (1% mass) of activation regents for high performance capacitive deionization. Graphical abstract Image 1 Highlights • The porous carbon derived from fruit waste was prepared via hydrothermal synthesis method. • The carbon activated with low amount (1% mass) of ZnCl 2 showed the best porous characteristics. • The ZnCl 2 -activated carbon exhibited the best electrochemical and desalination performance. • The +C-Zn||AC cell shows high desalination rate and excellent desalination and regeneration stability. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is an emerging electrochemical desalination technique for the energy- efficient removal of dissolved ions from aqueous solution. This is a first research attempt which describes the influence of dye molecules on capacitive deionization of salt solution. In this regard, a CDI flow cell has been fabricated and tested in order to scrutinize the electrosorptive removal of three different dye molecules such as amido black 10B (AB) (acidic dye), eosin yellow (EY) (neutral dye) and methyl violet (MV) (basic dye) from synthetic aqueous solutions. The electrosorption capacitance was analyzed by cyclic voltammetry cell and CDI flow cell using activated carbon cloth (ACC) electrodes with 1 cm 2 and 24 cm 2 surface areas respectively. The capacitance values of 106 and 99 F/g correspondingly were obtained for a steady-state CV and CDI flow cell with 50 mM Na 2 SO 4 electrolyte solution. In addition to this, the dye removal efficiency was also examined by a CDI flow cell for the solution containing 10 ppm of dye and 500 ppm of Na 2 SO 4 . The experimental results substantiate that EY exhibits strong adsorption during charging and strong desorption during discharge cycle when compared with other two dye molecules (AB & MV). Conclusively, electrosorption of dye molecules at the carbon cloth electrodes surface was found in the following order: EY > AB > MV. [ABSTRACT FROM AUTHOR]

Doping and high specific area are essential to the performance of supercapacitor electrode materials. However, the conventional single doping in two dimensional electrode materials is still unable to get high supercapacitive performance. Here we report a facile hydrothermal process using ammonia as a source of nitrogen (N) and thiourea as a sulfur (S) source to prepare N/S co-doped three dimensional (3D) graphene hydrogel (N/S-3DGH) for supercapacitor electrode application. The as-prepared N/S-3DGH is uniform and stable. The N/S co-doped 3DGH electrode material exhibits a high specific capacity of 1063 Cg -1 at a current density of 1 Ag -1 . Even at a density of 20 Ag -1 , it can still hold an excellent charge and discharge cycling stability, and with 76% of initial capacity retained after 6000 charge and discharge cycles at a density of 10 Ag -1 . Moreover, the all-symmetric solid-state supercapacitor fabricated by N/S-3DGH without any binders owned an energy density of 6.25 Wh kg −1 at a power density of 500 W kg −1 showing very promising applications for portable power and flexible energy storage devices. [ABSTRACT FROM AUTHOR]

The surface charge amplification (SCA) phenomenon at the ionic liquid/cavity interface has been investigated as a result of co-ion electrosorption due to increasing the alkyl chain length of imidazolium. Three types of ionic liquids with different imidazolium alkyl chain lengths inside the different-sized spherical cavities of porous electrodes have been studied using the coarse-grained model within the framework of classical density functional theory (CDFT). Our results show that selectivity occurs at lower potentials for ionic liquids with longer cation chain lengths in smaller cavities. The significant point is that at low negative surface potentials for asymmetric ionic liquids, the electrosorption of anions as co-ions occurs in some spatial regions that are made possible by the accidental orientation of cations in the first layer in the vicinity of the cavity surface. This is evidence of the SCA phenomenon for asymmetric ionic liquids at the ionic liquid/cavity interface. Moreover, the comparison of results, especially the normalized screening strength in the first layer indicates that the smaller cavities containing the ionic liquid with cations that have longer alkyl chains amplify the electrode surface charge more. [ABSTRACT FROM AUTHOR]

Desalination performance of capacitive deionization (CDI), a promising deionization technology, depends significantly upon the compositions and internal structures of electrode materials. Herein, hollow ZIFs-derived nanoporous carbons (HZCs) were prepared via chemical etching method and subsequent pyrolysis. Particularly, the tannic acid as an etching agent was employed to tailor hollow structure. The resultant HZCs possess high surface area, wide pore size distribution, obvious hollow cavity and high nitrogen content. Moreover, HZCs electrodes exhibited a significantly improved CDI performance over the solid ZIFs-derived nanoporous carbons (SZCs) electrodes. The improved electrosorption rate and capacity (15.31 mg g -1  at 1.2 V) of HZCs electrode imply that hollow structure facilitates the transportation for both ions and mass on CDI process. Besides, the further cycle experiment exhibits a great regeneration stability of HZCs electrode over 20 adsorption-desorption cycles. All these results indicate that HZCs should be a promising candidate for CDI application. [ABSTRACT FROM AUTHOR]

The growing popularity of Li-ion batteries in the field of energy storage necessitates the constant development of methods for improving their performance. To address this task, this study describes the effect of transition metal (TM = Al, Co, Fe) phosphate coatings on the electrochemical performance of Li 1.0 Ni 0.8 Co 0.15 Mn 0.05 O 2 positive electrode materials, highlighting the importance of the TM/P mole ratio, and reveals that decreased amounts of Li residuals were observed for all coated samples. Considering Li residual removal as well as capacity and capacity retention upon cycling, the most effective surface modification was achieved in the case of a 1:1 Co/P coating, which increased initial capacity and capacity retention by 10 mAh g −1 and 3%, respectively, as compared to the uncoated sample. Moreover, the beneficial effect of the above Co/P coating is also confirmed for the more Ni-rich Li 1.0 Ni 0.91 Co 0.06 Mn 0.03 O 2 . [ABSTRACT FROM AUTHOR]

MnO 2 films electrodeposited on carbon fibers were subjected to hydrothermal treatment in deionized water and a K 2 SO 4 solution. The effects of hydrothermal treatment on the structures and capacitive properties of the films were systematically evaluated. Compared to the as-deposited and K 2 SO 4 -treated films, the water-treated film exhibits a much lower capacitance at 2 mV s −1 due to the phase transformation from ramsdellite to manganite during the hydrothermal treatment. The K 2 SO 4 -treated film maintains the ramsdellite structure although the average oxidation state of Mn in the film is decreased to some extent. At the charge-discharge current density of 1C, the K 2 SO 4 -treated and as-deposited films show specific capacitances of 281.9 and 274.7 F g −1 , respectively. But the K 2 SO 4 -treated film displays a capacitance of 135 F g −1 at 15C and a good high-rate capability which is more than 3 times as high as that of the as-deposited one. These results and the related kinetic analysis suggest that the suitable ratio of Mn 4+ to Mn 3+ plays an important role in determination of the high-rate capability of the film. [ABSTRACT FROM AUTHOR]

The growing ubiquity of recalcitrant organic contaminants in the aqueous environment poses risks to effective and efficient water treatment and reuse. A novel three-dimensional (3D) electrochemical flow-through reactor employing activated carbon (AC) encased in a stainless-steel (SS) mesh as a cathode is proposed for the removal and degradation of a model recalcitrant contaminant p -nitrophenol (PNP), a toxic compound that is not easily biodegradable or naturally photolyzed, can accumulate and lead to adverse environmental health outcomes, and is one of the more frequently detected pollutants in the environment. As a stable 3D electrode, granular AC supported by a SS mesh frame as a cathode is hypothesized to 1) electrogenerate H 2 O 2 via a 2-electron oxygen reduction reaction on the AC surface, 2) initiate decomposition of this electrogenerated H 2 O 2 to form hydroxyl radicals on catalytic sites of the AC surface 3) remove PNP molecules from the waste stream via adsorption, and 4) co-locate the PNP contaminant on the carbon surface to allow for oxidation by formed hydroxyl radicals. Additionally, this design is utilized to electrochemically regenerate the AC within the cathode that is significantly saturated with PNP to allow for environmentally friendly and economic reuse of this material. Under flow conditions with optimized parameters, the 3D AC electrode is nearly 20% more effective than traditional adsorption in removing PNP. 30 grams of AC within the 3D electrode can remove 100% of the PNP compound and 92% of TOC under flow. The carbon within the 3D cathode can be electrochemically regenerated in the proposed flow system and design thereby increasing the adsorptive capacity by 60%. Moreover, in combination with continuous electrochemical treatment, the total PNP removal is enhanced by 115% over adsorption. It is anticipated this platform holds great promises to eliminate analogous contaminants as well as mixtures. [Display omitted] [ABSTRACT FROM AUTHOR]

• The ZnWO 4 is a new type of electrode with non-Faradaic capacitive behavior. • The ZnWO 4 electrode exhibits a superior volumetric specific capacitance. • This work provides a new material system for the pseudocapacitive field. Pseudocapacitive behavior is one of the most concerned basic scientific issues in the electrochemical field. How to distinguish capacitive, pseudocapacitive and battery behavior accurately remains as a difficult problem. In addition, the capacitive charge storage mechanism of the non-Faraday process has been found in non-carbon-based materials in ways that challenge established theory. This is also the difficulty in defining the electrochemical behavior of newly discovered materials. Here, we report the pseudocapacitance behavior of sanmartinite (ZnWO 4) for the first time. Under aqueous system conditions, the cyclic voltammetry curves of ZnWO 4 present the ideal rectangle shape, and the galvanostatic charge/discharge curves exhibit the isosceles triangle shape. In addition, the calculated value of b is 0.88, which further indicates that the kinetic process is controlled by the surface capacitance. [Display omitted]. [ABSTRACT FROM AUTHOR]

Activated carbon (AC) has been widely used to prepare electrode sheet for capacitive deionization (CDI) owing to its high surface area for ionic adsorption. However, further modification of the AC electrode is still necessary to improve the CDI performance by enhancing the ionic transportation inside the electrode. Here, an asymmetric CDI cell was prepared using Nafion-AC composite with low PTFE content (3.5%) as the negative electrode and AC as the positive electrode. Nafion functions not only as a binder to improve the adhesion of electrode sheet, but also as a mediator to provide an ion conductive pathway for counterions. The morphology and elemental analysis of Nafion-AC were investigated via scanning electron microscopy (SEM) and elemental mapping. The electrochemical capacitance property of the Nafion-AC electrode was studied by cyclic voltammetry (CV). The desalination capacity of the asymmetric CDI cell arrived at 10.8 mg/g, compared with the symmetric AC-based cell (6.9 mg/g). Contribution of Nafion and the corresponding mechanism were analyzed by differential capacitance tests and inverse charging. It demonstrates that in the Nafion-AC composite containing low PTFE content, the co-ion repulsion was reduced and the electrode adhesion was improved. The electrode performance has been conveniently evaluated by monitoring the variation of the charging efficiency and desalination amount with time under an appropriate charge input, which is much helpful to guide the operation process in practical CDI applications. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is a promising technology for the desalination of brackish water due to its potentially high energy efficiency and its relatively low costs. One of the most challenging issues limiting current CDI cell performance is poor cycling stability. CDI can show highly reproducible salt adsorption capacities (SACs) for hundreds of cycles in oxygen-free electrolyte, but by contrast poor stability when oxygen is present due to a gradual oxidation of the carbon anode. This oxidation leads to increased concentration of oxygen-containing surface functional groups within the micropores of the carbon anode, increasing parasitic co-ion current and decreasing SAC. In this work, activated carbon (AC) was chemically modified with titania to achieve additional catalytic activity for oxygen-reduction reactions on the electrodes, preventing oxygen from participating in carbon oxidation. Using this approach, we show that the SAC can be increased and the cycling stability prolonged in electrochemically highly demanding oxygen-saturated saline media (5 mM NaCl). The electrochemical oxygen reduction reaction (ORR) occurring in our CDI cell was evaluated by the number of electron transfers during charging and discharging. It was found that, depending on the amount of titania, different ORR pathways take place. A loading of 15 mass% titania presents the best CDI performance and also demonstrates a favorable three-electron transfer ORR. [ABSTRACT FROM AUTHOR]

Capacitive neutralization deionization with flow electrodes (FCND) was proposed by combining neutralization dialysis (ND) and flow-electrode capacitive deionization (FCDI). Its key property is that by employing flow electrodes, capacitive adsorption of salt ions occurs simultaneously during the neutralization dialysis process. To compare the desalination performance between FCND and FCDI, a series of experiments were conducted by changing salt concentration and applied electrical voltage. The hybrid exhibits a promising average salt adsorption rate (ASAR) and salt removal efficiency (SRE) compared to either ND or FCDI process. The ASAR and SRE of FCND are 203.27 mmol m −2 min −1 and 72.20% in 0.1 mM NaCl solution at 1.2 V after 120 min, whereas the values of FCDI are 120.86 mmol m −2 min −1 and 42.92%, respectively. In order to facilitate the understanding of the ion transportation in this complex system, a theory was also set up based on simplified Nernst-Planck equation and Donnan equilibrium, which helps to understand the experimental data. [ABSTRACT FROM AUTHOR]

Graphene is a promising electrode material for high performance supercapacitors and capacitive deionization applications. Our present work is focused on the synthesis of graphene nanosheets by the reduction of graphite oxide using focused solar irradiation. The as prepared graphene nanosheets are characterized by Transmission Electron Microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS) and Fourier transform infrared spectroscopic (FTIR) techniques for surface, structural and functional group analysis. Electrochemical properties are studied using cyclic voltammetry and galvanostatic charge-discharge method. The fabricated supercapacitor cell shows high specific capacitance of 265.9 and 187.1 F g −1 with 6 M KOH and ionic liquid electrolyte (EMIMBF 4 ), respectively. High energy density of 58.5 Wh Kg −1 has been obtained for EMIMBF 4 electrolyte. The electrosorption studies were also performed to study the effect of deionization behaviour of the prepared graphene under flow in between electrodes technique. The electrosortion capacity of 22.4 mg/g has been obtained for 100 mM NaCl (∼5844 mg/l) solution at the applied voltage of 1 V. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is an emerging technology that supplies deionized water to resolve the fresh water shortage. CDI electrodes are mainly made up of carbon materials, of which the deionization performance is closely related to their physical properties and structures. Hence, a rational design of electrode material structure is essentially significant. Functionalized graphene (fG) in particular has recently been regarded as characteristic CDI electrode material. However, preparation of fG based on graphene oxide usually results in serious secondary pollution due to usage of highly poisonous chemicals, and thus still cannot meet the demand of practical application. It is feasible that environmentally-friendly activated carbon (AC) and small amounts of fGs can be combined rationally, and used as CDI electrodes. Here, sono-assembled AC/m-phenylenediamine (mPEA) or p-phenylenediaminefG inter-connected network architecture has been constructed for the first time successfully. The specific capacitances of the AC/fG composites were found to be significantly higher than that of the AC electrode owing to mesoporous generation. Also, among all the samples, the AC composite with 5 wt % mPEA-fG exhibited an ultrahigh electrosorption capacity of 12.58 mg/g (or 0.22 mmol/g) in NaCl solution. These observations indicate that fG can serve as an efficient conductive bridge to decrease the aggregation of AC particles, and improve the electron transfer with the composite electrode. This work provides an effective strategy for the environmental and economical electrode architectures for general applications in CDI and energy storage. [ABSTRACT FROM AUTHOR]

• Sub-10 nm SnO 2 -In 2 O 3 heterostructures was fabricated by ALD technique. • The thin-film of heterostructure could significantly increase the performance of ESC. • The heterostructure electrode delivered a high specific capacitance of 757 F g−1. • Results demonstrate that thin-film electrode is promising for high-performance ESCs. Fabrication of thin-film heterostructured electrodes with thickness below 10.0 nm is of great importance for the development of high-performance electrochemical supercapacitors (ESCs) with great capabilities. This is because such electrodes with uniform thicknesses enable fast electrochemical responses during charging/discharging ascribed to their short charge and ion diffusion lengths. In this study, two-dimensional (2D) SnO 2 -In 2 O 3 heterostructures with a thickness of ∼7.84 nm was fabricated on Au/SiO 2 /Si wafers by the atomic layer deposition (ALD) technique for ESCs application. Various spectroscopic and microscopic analyses demonstrated the formation of 2D SnO 2 -In 2 O 3 heterojunction with high purity, crystallinity and homogeneous morphology. Cyclic voltammetry (CV) measurements revealed the pseudocapacitive Faradaic redox reactions with good reversibility for 2D SnO 2 -In 2 O 3 heterostructure. The heterostructured electrodes demonstrated excellent super-capacitive performance with high specific capacitance (C s) up to 1048.25 and 757 F g−1 at the scan rate and the current density of 10 mV s−1 and 12 A g−1, respectively. Accordingly, a high energy density of 51.55 Wh kg−1 is attained at 12 A g−1. The high super-capacitive performance of these heterostructures can be attributed to the improved redox activity and short ion diffusion length of the SnO 2 -In 2 O 3 nanohybrid thin-film. The electrodes also demonstrated great electrochemical stability with the C s retention of 96.15% even after 5000 charge/discharge cycles. [Display omitted] [ABSTRACT FROM AUTHOR]

Flow electrode capacitive deionization (FCDI) has great advantages in high salinity wastewater desalination. However, due to the limited adsorption capacity of electrode material, membrane concentration polarization would form and increase energy consumption, and affect the continuity of desalination. In this work, milling technology was used to modify original activated carbon (AC), the obtained ball milled activated carbon (BAC) was used as FCDI electrode material. The milling process modified multiple physical and electrochemical characteristics of original AC. The highest average salt removal rate (ASRR) of BAC was 2.2 times of that of AC, which was attributed to the modified surface properties including more oxygenated functional group, larger electrostatic gravitation characteristics and better hydrophilicity. The reduced concentration polarization during the desalination was responsible for the increased adsorption capacity, which was due to larger electrolyte contact area, enhanced ions capacity by more suitable pore structures, and 5 times higher energy normalized removal salt (ENRS) of BAC flow electrode than that of AC. Because of its simple operation and remarkable modification effect, ball milling technology shows great potential in large scale modification of electrode materials. [ABSTRACT FROM AUTHOR]

• La-doping HAP (La-HAP) was synthesized by hydrothermal method in the presence of LaCl 3. • LaHAP/3D-rGO composites with various ratios were obtained by simple ultrasonic mixing. • 50LaHAP/3D-rGO possesses good conductivity and high hydrophilicity. • 50LaHAP/3D-rGO delivers F− adsorption of 1132 μmol g−1 with high selectivity by CDI. • The selective removal of F- in actual high-fluorine groundwater is achieved. Excessive fluoride in water is severely hazardous to environment and human health. It is of great significance to exploit effective methods for defluoridation from water. In this paper, lanthanum-doped hydroxyapatite modified three-dimensional reduced graphene oxide (LaHAP/3D-rGO) was successfully synthesized with LaHAP uniformly distributed on the 3D network. Electrochemical characterization demonstrates the improvement of the conductivity and ion diffusion rate after doping appropriate amount of LaHAP. With LaHAP/3D-rGO as positive electrode (activated carbon as negative electrode), the corresponding capacitive deionization (CDI) system is successfully applied for the selective adsorption of fluoride. With the appropriate LaHAP/3D-rGO ratio (50%), the obtained LaHAP/3D-rGO electrode achieves the optimal F− adsorption amount of 1132 μmol g−1. The corresponding CDI cell shows excellent selectivity and high cycle stability for adsorption of fluoride. When applied to the fluoride removal in the fluoride-containing groundwater through a 3-cell CDI stack, the electrode attains the high F− removal rate of 90.5%, with the effluent concentration down to 0.32 mg L−1, much lower than the permissible limit of World Health Organization. This LaHAP/3D-rGO based CDI system is much promising for water purification of the high F− groundwater. [Display omitted] [ABSTRACT FROM AUTHOR]

• La-0.5% was less affected by the presence of competing anions than La-1.5%. • Chemisorption and electrosorption mechanisms in La-0.5% reduced the interference by other anions. • Charge and hydration played the major role in selectivity. • Hydroxyls from the La(III) clusters were exchanged by the studied anions. Here it is reported the electrosorption of fluoride in the presence of competing anions of environmental relevance (chloride, nitrate, sulfate, phosphate and arsenate) by two activated carbon electrodes impregnated with La(III), La-0.5% and La-1.5% (w/w %). The electrosorption kinetics were evaluated using equimolar initial concentrations (0.263 mM of each studied anion) in both binary solutions (F− vs. anion) and in a complex mixture comprising all anions simultaneously. For La-0.5%, the presence of nitrate and chloride did not significantly modify its fluoride removal (q = ∼19.25 µmol g−1), while these same anions decreased the fluoride removal of La-1.5% from 32.85 to 17.2 and 13.95 µmol g−1, for nitrate and chloride, respectively. In general, the divalent anions competed the most during the kinetics, decreasing the fluoride removal in both carbons; the lowest capacity values were 5.75 and 4 µmol g−1 for La-0.5% and La-1.5%, respectively. The increases in the pH of the solution corroborated that all anions anchored to the modified surface by a ligand-exchange mechanism involving the exposed hydroxyls from the La(III) clusters. The discussion of the results was not centered on the charge and the hydrated radius of the anions, but it was also expanded to other thermodynamic parameters that also denote selectivity, such as the hydration energies and mass-transport parameters. Electrochemical impedance spectroscopy was performed as a characterization technique in two electrolytes: 0.1 M NaF and the working solution, 0.263 mM NaF (5 ppm F− solution). The information obtained from the latter correlated the most with the electrosorption performance of the electrodes. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) which removes ionic species from solution by applying electric energy to carbon based electrodes is one of excellent convergence technologies combined with energy storage technology and environmental systems. In recent decades, the technology for synthesizing new carbon materials has advanced, the electrical double layer capacitance in porous structures has become better understood, and novel deionization systems have been developed. Nevertheless, achieving a higher deionization performance is required for CDI to compete with reverse osmosis for deionization. The recently introduced Hybrid CDI (HCDI), which utilizes sodium manganese oxide (Na 4 Mn 9 O 18 ) and carbon material, successfully demonstrated its superior deionization performance over conventional CDI systems. Despite the great promise of the HCDI system, the limited availability of aqueous based intercalation materials and the lack of information regarding the characteristics of the HCDI system operations are obstacles to the advancement of HCDI. Thus, we report a new HCDI system with sodium iron pyrophosphate (Na 2 FeP 2 O 7 ), which is a promising material for sodium ion batteries due to its high capacity, low cost and environmentally benign nature. The major results of the HCDI system with Na 2 FeP 2 O 7 showed a superior maximum deionization rate performance (0.081 mg g −1 s −1 ) with a comparable deionization capacity (30.2 mg g −1 ) compared to the previous HCDI system with Na 4 Mn 9 O 18 . Furthermore, the analysis of the CDI Ragone plot revealed the hybrid behavior characteristics of this HCDI system and that the high deionization capacity originated from the high capacity of Na 2 FeP 2 O 7 at a low current density, whereas the fast deionization rate originated from the supercapacitor system at a high current density. Consequently, this study on a new HCDI system with Na 2 FeP 2 O 7 contributes to expanding the understanding of the kinetic properties of the HCDI system with respect to its diverse operations. [ABSTRACT FROM AUTHOR]

Here a facile strategy was proposed to prepare graphene (GE) sheets with unique mesoporous morphology (denoted as mGE) via a simple carbothermal reaction by using KMnO 4 as the etching agent. The morphology, structure and electrochemical properties of mGE were investigated by scanning electron microscopy, transmission electron microscopy, Raman spectra, nitrogen adsorption-desorption, cyclic voltammetry and electrochemical impedance spectroscopy. The electrosorption performance of mGE in NaCl solution was studied and compared with GE. The results show that mGE electrode exhibits a high electrosorption capacity of 6.38 mg g −1 when the initial NaCl concentration is ∼75 mg L −1 and applied voltage is 1.2 V, which is about 2.3 and 1.5 times of those of GE (2.76 mg g −1 ) and recently reported microporous GE (∼4 mg g −1 ), respectively, and also higher than those of other carbon materials in the literatures, due to short ion diffusion path, large accessible surface area and low charge transfer resistance offered by its novel mesoporous structure. Therefore, it is believed that mGE is a promising candidate for practical capacitive deionization applications. [ABSTRACT FROM AUTHOR]

In capacitive deionization (CDI), co-ions will be repelled simultaneously from the electrodes when counterions are adsorbed onto the electrodes, leading to a diminished CDI performance. To reduce this so-called co-ion effect, carboxylic groups were grafted onto the surface of commercial activated carbon fiber (ACF) using a simple nitric acid treatment (ACF-HNO 3 ). ACF-HNO 3 exhibited good cation selectivity. An asymmetric CDI cell (N-CDI) was assembled, in which ACF-HNO 3 was used as the cathode and pristine ACF as the anode. The removal capacity of N-CDI at 1.2 V can be as high as 12.8 mg/g, whereas that of the symmetric CDI cell composed of pristine ACF (0-CDI) is only 8.0 mg/g. Accordingly, the charge efficiency of N-CDI stays above 74%, whereas that of 0-CDI is below 40% at various applied voltages. Moreover, N-CDI exhibited better cyclic stability than 0-CDI. These results indicate that use of ACF-HNO 3 as the cathode can effectively reduce co-ion expulsion, thereby enhancing the CDI performance. [ABSTRACT FROM AUTHOR]

Today's electrochemical energy storage technologies aim to combine high specific energy and power, as well as long cycle life, into one system to meet increasing demands in performance. These properties, however, are often characteristic of either batteries (high specific energy) or capacitors (high specific power and cyclability). To merge battery- and capacitor-like properties in a hybrid energy storage system, researchers must understand and control the co-existence of multiple charge storage mechanisms. Charge storage mechanisms can be classified as faradaic, capacitive, or pseudocapacitive, where their relative contributions determine the operating principles and electrochemical performance of the system. Hybrid electrochemical energy storage systems can be better understood and analyzed if the primary charge storage mechanism is identified correctly. This tutorial review first defines faradaic and capacitive charge storage mechanisms and then clarifies the definition of pseudocapacitance using a physically intuitive framework. Then, we discuss strategies that enable these charge storage mechanisms to be quantitatively disentangled using common electrochemical techniques. Finally, we outline representative hybrid energy storage systems that combine the electrochemical characteristics of batteries, capacitors and pseudocapacitors. Modern examples are analyzed while step-by-step guides are provided for all mentioned experimental methods in the Supplementary Information. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper reports a graphene oxide (GO) confined strategy to synthesize reduced GO-coated lithium titanate (Li 4 Ti 5 O 12, LTO) microspheres using as-prepared TiO 2 microspheres and GO as raw materials. The obtained samples are characterized by X-ray diffraction, field emission scanning electron microscopy and spectrophotometer. Results show that the spherical LTO is formed with approximate 1 μm diameter after hydrothermal reactions, which is due to a confined effect of GO on the surface of TiO 2 spheres. Electrochemical tests reveal that the presence of rGO can increase the capacity and cycling stability of LTO anodes, especially at higher C rate. The 3 wt% rGO-coated LTO anodes present a higher reversible Li-ion storage with a specific discharge capacity of 131.6 mAh g −1 at 5 C and 97% retention even after 500 cycles, which are more excellent than those of pristine LTO. The GO-confined method is anticipated to synthesize other electrode materials with high electrochemical performances. [ABSTRACT FROM AUTHOR]

Electrochemical Impedance Spectroscopy (EIS) has been used to explore the corrosion and electrochemical behavior of 1018 mild steel (MS) in deaerated, deionized water containing different concentrations of the filming amine inhibitor Anodamine. The Point Defect Model (PDM) was optimized on the EIS data using the newly-developed procedure to study the mitigation mechanism of Anodamine. The optimization results suggest that, as the concentration of Anodamine increases, the pore resistance of the adsorbed inhibitor, the charge transfer resistance, and the Warburg coefficient associated with the transport of redox species through the porous outer layer of the passive film increase, with the latter being the primary cause of inhibition. Accordingly, the hydrophobic layer of adsorbed Anodamine becomes more protective and the inhibitory effect of Anodamine is enhanced as its concentration increases. In addition, within the passive range, increased applied anodic potential enhances the adsorption of Anodamine and hence enhances its inhibitory effect. [ABSTRACT FROM AUTHOR]