Activated Carbon Cloth Electrodes Research Articles

Mechanisms of the performance fading of carbon-based electrochemical capacitors operating in a LiNO3 electrolyte

This paper reports on the ageing mechanisms in symmetric, carbon/carbon electrochemical capacitors operating with a 1 mol⋅L−1 LiNO3 aqueous electrolyte. The carbon electrodes were subjected to a constant polarization protocol (i.e., floating) at various voltages and were analysed post-mortem by N2 sorption at 77 K, Raman spectroscopy, Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), and elemental analysis. This approach allowed real capacitor performance deterioration to be simulated. Herein, the relationship between the electrochemical performance of high-voltage aqueous capacitors and the porosity of activated carbon cloth electrodes was investigated. Interestingly, two different ageing mechanisms, which mainly depended on the applied voltage, were identified. The oxidation of the positive electrode was the main reason for the capacitance fading. However, the oxidation of carbon was not the only reason, and it was postulated that solid-state deposits originating from CO and CO2 evolution block the electrode pores and induce capacitance fading. A proof-of-concept experiment presented in this paper confirmed a partial electrode surface recovery after ageing.

Communication—Porous Activated Carbon from Amorphophallus Konjac by One Step Method for High Performance Supercapacitors

Porous activated carbons (AC) have been synthesized from natural biomass material amorphophallus konjac powder by one-step method to make a carbonization and activation with potassium hydroxide. The three-electrode system tests show that the porous structure KGAC-X samples have excellent electrochemical performance, especially the KGAC-2 electrode showing superior specific capacitance (169.8 F g−1, current density 1 A g−1) and excellent rate performance (212.5 F g−1, current density 1 A g−1) in the 1 M KOH electrolyte. This study provides a facile, economical, and effective route to prepare commercial activated carbon electrode material with high porosity for supercapacitors.

Low-cost, high-performance supercapacitor based on activated carbon electrode materials derived from baobab fruit shells

Due to an effective synthesis strategy, two kinds of hierarchical porous activated carbons were derived via KOH and H3PO4 activation and carbonization processes from baobab fruit shells (BFSs) used as a green and low-cost biomass precursor. The physicochemical properties and the morphological structure of the baobab fruit shell derived carbons (BFSCs) were systematically studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectra, nitrogen adsorption/desorption isotherms and X-ray photoelectron spectroscopy (XPS) techniques. The biomass-derived activated carbons, BFSC1 (using KOH activation), and BFSC2 (using H3PO4 activation), obtained exhibit high specific capacitances of 233.48 F g−1 and 355.8 F g−1 at a current density of 1 A g−1, respectively, due to their different surface structures and high specific surface areas. Furthermore, the as-assembled, flexible all-solid-state supercapacitor devices based on the BFSC electrodes exhibit a high specific capacitance of 58.67 F g−1 at 1 A g−1 and a high energy density of 20.86 Wh kg−1 at a power density of 400 W kg−1. This facile route highlights the exciting possibility of utilizing waste baobab fruit shells to produce low-cost, green and high-performance carbon-based electrode materials for sustainable electrochemical energy storage systems.

A comparative study on electrosorptive rates of metal ions in capacitive deionization

A comparative study on electrosorptive rates was conducted to explore the affinity preference of Na+, K+, Mg2+, Ca2+, Cd2+, Pb2+ and Cu2+ to activated carbon cloth electrodes of capacitive deionization (CDI) in mono-component solutions. Results showed the electrosorptive kinetics of these metal ions followed the Lagergren equation. For alkali and alkali-earth metal ions, the order of electrosorptive rates followed K+ > Na+ > Ca2+ > Mg2+, which revealed an inversely proportional relationship with their ionic hydrated radii. The relationship between electrosorptive rates and ionic hydrated radii, however, did not hold for heavy metal ions, and the order was Cu2+ > Pb2+ > Cd2+. The abnormal electrosorptive behaviors of Cu2+ and Pb2+ could be attributed to electrodeposition and formation of OH− complexes during electrosorption. Besides, Cu2+ and Pb2+ showed significantly low desorption efficiencies during the electrode regeneration processes, indicating serious electrode fouling during the electrosorptive process. This work provides fundamental aspects on individual removal of metal ions and the results can be beneficially used as a reference for treatment and recovery of metal ions by CDI technology.

Promising post-consumer PET-derived activated carbon electrode material for non-enzymatic electrochemical determination of carbofuran hydrolysate

In this work, activated carbon (AC) materials, prepared from polyethylene terephthalate (PET) waste bottles were used as the sensing platform for the indirect detection of carbofuran. The morphology and surface properties of the PET-derived AC (PET-AC) were characterized by N2 adsorption/desorption isotherm, X-ray diffraction (XRD), field-emission scanning/transmission electron microscopy (FE-SEM/TEM) and Raman spectroscopy. The electrochemical activity of the PET-AC modified glassy carbon electrode (GCE) (PET-AC/GCE) was measured by cyclic voltammetry and amperometry. The enhanced surface area and desirable porosities of PET-AC are attributed for the superior electrocatalytic activity on the detection of carbofuran phenol, where, the proposed sensor shows low detection limit (0.03 µM) and remarkable sensitivity (0.11 µA µM−1 cm−2). The PET-AC/GCE holds high selectivity towards potentially interfering species. It also provides desirable stability, repeatability and reproducibility on detection of carbofuran phenol. Furthermore, the proposed sensor is utilized for the detection of carbofuran phenol in real sample applications. The above mentioned unique properties and desirable electrochemical performances suggest that the PET-derived AC is the most suitable carbonaceous materials for cost-effective and non-enzymatic electrochemical sensor.

Confined Redox Reactions of Iodide in Carbon Nanopores for Fast and Energy-Efficient Desalination of Brackish Water and Seawater.

Faradaic deionization is a promising new seawater desalination technology with low energy consumption. One drawback is the low water production rate as a result of the limited kinetics of the ion intercalation and insertion processes. We introduce the redox activities of iodide confined in carbon nanopores for electrochemical desalination. A fast desalination process was enabled by diffusionless redox kinetics governed by thin-layer electrochemistry. A cell was designed with an activated carbon cloth electrode in NaI aqueous solution, which was separated from the feedwater channel by a cation-exchange membrane. Coupled with an activated carbon counter electrode and an anion-exchange membrane, the half-cell in NaI with a cation-exchange membrane maintained performance even at a high current of 2.5 A g-1 (21 mA cm-2 ). The redox activities of iodide allowed a high desalination capacity of 69 mg g-1 (normalized by the mass of the working electrode) with stable performance over 120 cycles. Additionally, we provide a new analytical method for unique performance evaluation under single-pass flow conditions regarding the water production rate and energy consumption. Our cell concept provides flexible performance for low and high salinity and, thus, enables the desalination of brackish water or seawater. Particularly, we found a low energy consumption (1.63 Wh L-1 ) for seawater desalination and a high water production rate (25 L m-2 h-1 ) for brackish water.

Investigation on the effect of organic dye molecules on capacitive deionization of sodium sulfate salt solution using activated carbon cloth electrodes

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 cm2 and 24 cm2 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 Na2SO4 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 Na2SO4. 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.

Bromide Ions Specific Removal and Recovery by Electrochemical Desalination.

Removal and recovery of bromide ions by electro-oxidation and electro-reduction are presented using hybrid physical adsorption and capacitive deionization cells, which contain activated carbon cloth electrodes. This is a proof of concept research with results, which indicate that when comparing the removal and recovery quantities of bromide and chloride ions (starting with the same initial concentration of 0.05 M for both salts), the desalination capacity of the bromide ions is larger by almost 2 orders of magnitude than that of the chloride ions; thus, we obtained specific desalination of bromide ions from a solution containing chloride ions. Removal and recovery of 3.5 mmol of bromide ions were achieved by a working electrode with 1 g of activated carbon cloth, and the calculated energy consumption for the removal and recovery of 1 g of bromide ions was about 2.24 kJ/g.

Influence of thermal treatment conditions on capacitive deionization performance and charge efficiency of carbon electrodes

In this study, effects of thermal treatment conditions on the capacitive deionization performance (CDI) of activated carbon cloth (ACC) electrodes have been investigated. A total of 8 different treatment conditions has been studied by systematically changing the type of gas (Ar, CO2, N2) and the treatment temperature (700, 800, 850 °C). Treated electrodes were subjected to electrochemical testing and morphological analysis in order to assess the changes in the CDI performance. Results indicated a major discrepancy between the electrochemical and the CDI performance of the treated electrodes depending on the treatment condition. For instance, electrochemical testing showed 15% improvement in charge storage for N2-treated electrodes, while CDI performance was found to decrease by 20%. On the other hand, improvements in both electrochemical (25%) and CDI performances (60%) were observed for Ar and CO2 treated electrodes. These findings indicate that different treatment conditions promote distinct charge compensation mechanisms at the electrode surface; some of which are not beneficial for salt adsorption. Moreover, results highlight the significance of selecting a suitable thermal treatment condition for achieving enhanced performance in CDI systems utilizing ACC electrodes.

Research on super capacitance properties of modified activated carbon in sodium sulfate electrolyte

In order to improve the specific capacity and energy density of activated carbon electrode materials activated carbon was modified by surface treatment using hydrogen peroxide. The modified carbons were characterized the changes of pore structure and functional groups before and after modification by N2 adsorption-desorption isotherms and FTIR spectroscopy. The three electrode system was assembled with modified activated carbon as electrode materials and Na2SO4 as the electrolyte. The influence of surface modification on the performance of EDLCs was studied by galvanostatic charge-discharge, cyclic voltammetry, and alternating current impedance. The results show that the surface chemistry of the modified activated carbon material has changed, the specific surface area has changed and the pore size has not changed much with the introduction of new oxygen-containing functional groups. The specific capacity of the activated carbon material modified by 5h is 75F/g, which is 86.1% higher than that before the modification. It can be seen that the change of functional group after the modification of activated carbon can help to increase the specific capacity.

Understanding of carbon-based supercapacitors ageing mechanisms by electrochemical and analytical methods

In order to shed light on ageing mechanisms of Electrochemical Double Layer Capacitor (EDLC), two kinds of activated carbons are studied in tetraethyl ammonium tetrafluoroborate (Et4NBF4) in acetonitrile. In floating mode, it turns out that two different ageing mechanisms are observed, depending on the activated carbon electrode materials used. On one hand, carbon A exhibits a continuous capacitance and series resistance fall-off; on the other hand, for carbon B, only the series resistance degrades after ageing while the capacitance keeps unchanged. Additional electrochemical characterizations (Electrochemical Impedance Spectroscopy – EIS – and diffusion coefficient calculations) were carried out showing that carbon A's ageing behavior is suspected to be primarily related to the carbon degradation while for carbon B a passivation occurs leading to the formation of a Solid Electrolyte Interphase-Like (SEI-L) film. These hypotheses are supported by TG-IR and Raman spectroscopy analysis. The outcome forms the latter is an increase of carbon defects on carbon A on positive electrode.

Capacitive Deionization Performance of Thermally Surface Modified Activated Carbon Cloth Electrodes

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.

Nanoporous activated carbon cloth as a versatile material for hydrogen adsorption, selective gas separation and electrochemical energy storage

The efficient storage of energy combined with a minimum carbon footprint is still considered one of the major challenges towards the transition to a progressive, sustainable and environmental friendly society on a global scale. The energy storage in pure chemical form using gas carriers with high heating values, including H2 and CH4, as well as via electrochemical means using state-of-the-art devices, such as batteries or supercapacitors, are two of the most attractive alternatives for the combustion of finite, carbon-rich and environmentally harmful fossil fuels, such as diesel and gasoline. A few-step, reproducible and scalable method is presented in this study for the preparation of an ultra-microporous (average pore size around 0.6nm) activated carbon cloth (ACC) with large specific area (> 1200m2/g) and pore volume (~ 0.5cm3/g) upon combining chemical impregnation, carbonization and CO2 activation of a low-cost cellulose-based polymeric fabric. The ACC material shows a versatile character towards three different applications, including H2 storage via cryo-adsorption, separation of energy-dense CO2/CH4 mixtures via selective adsorption and electrochemical energy storage using supercapacitor technology. Fully reversible H2 uptake capacities in excess of 3.1wt% at 77K and ~ 72bar along with a significant heat of adsorption value of up to 8.4kJ/mol for low surface coverage have been found. Upon incorporation of low-pressure sorption data in the ideal adsorbed solution theory model, the ACC is predicted to selectively adsorb about 4.5 times more CO2 than CH4 in ambient conditions and thus represents an appealing adsorbent for the purification of such gaseous mixtures. Finally, an electric double-layer capacitor device was assembled and tested for its electrochemical performance, constructed of binder-free and flexible ACC electrodes and aqueous CsCl electrolyte. The full-cell exhibits a gravimetric capacitance of ~ 121F/g for a specific current of 0.02A/g, which relative to the ACC's specific area, is superior to commercially available activated carbons. A capacitance retention of more than 97% was observed after 10,000 charging/discharging cycles, thus indicating the ACC's suitability for demanding and high-performance energy storage on a commercial scale. The enhanced performance in all tested applications seems to be attributed to the mean ultra-micropore size of the ACC material instead of the available specific area and/or pore volume.

Multiple Functional Biomass‐Derived Activated Carbon Materials for Aqueous Supercapacitors, Lithium‐Ion Capacitors and Lithium‐Sulfur Batteries

AbstractBiomass‐derived activated carbon electrode materials have been synthesized by carbonization and KOH activation processes from an agriculture waste − rice husk, composed of organic compound and silica. The surface area of activated carbon reached 1098.1 m2/g mainly including mesopores and macropores due to the template effect of silica in rice husk. Owing to the existence of mesopores and macropores, the as‐obtained activated carbon materials can be used in aqueous supercapacitors, lithium‐ion (Li‐ion) capacitors and lithium‐sulfur (Li‐S) batteries. In KOH electrolyte, fast rate performance (as high as 2 V/s) was obtained due to the existence of ideal electrical double layer capacitance. In organic electrolyte, high voltage (2.5 V) was achieved. Activated carbon electrode for Li‐ion capacitor also showed capacity of 17 mAh/g at 100 mA/g with the high voltage range of 2.5 V. The capacities of sulfur‐activated carbon in Li‐S batteries were 1230 and 970 mAh/g at the current densities of 0.1 and 0.2 C. The present results showed that activated carbon materials with mesopores were good host to immobilize polysulfides.

All-printed paper based surface mountable supercapacitors

Supercapacitors have drawn numerous attentions in recent years since they can deliver relatively high power and energy densities. This article introduces an all-printed paper based surface mountable supercapacitor (SMS), which could withstand the reflow soldering process when integrated into microelectronic systems. The device was fabricated by screen printing and stencil printing processes, contributing to low cost and large-scale fabrication. Furthermore, building electronic devices on ubiquitous paper substrates had advantages of light weight, low cost, and eco-friendliness, etc. Based on activated carbon electrode material and ionic liquid electrolyte, the capacity of the supercapacitor could reach 14 mF at the device volume of 3.2 mm × 2.5 mm × 0.175 mm, besides, the specific volumetric capacity was superior than most of the commercial SMS devices.

Biomass-Based Fuels and Activated Carbon Electrode Materials: An Integrated Approach to Green Energy Systems

Although pyrolysis holds promise for extracting biofuels from biomass, the low value of the biochar produced, combined with process energy requirements, make thermochemical conversion marginally viable. Likewise, while supercapacitors and fuel cells may satisfy growing demands for portable electronics and electric vehicles, current fossil-fuel based activated carbon electrodes are not sustainable. Both of these issues are addressed using a new approach to the integrated biorefinery. Pyrolysis of pistachio nutshell biomass yields a bio-oil high in benzenediols and pyrolysis gas enriched in methane and hydrogen. By impregnating the biochars produced via pyrolysis with potassium hydroxide, followed by heat treatment in an inert atmosphere, the total biofuel yield increased up to 25% while producing high surface area (>1900 m2/g) activated carbon biochar for use in electrochemical cells. Coin cell electrodes fabricated with these sustainable activated carbons provide almost 100% coulombic efficiency over 4000...

Study on the Aqueous Hybrid Supercapacitor Based on Carbon-coated NaTi2(PO4)3 and Activated Carbon Electrode Materials

Study on the Aqueous Hybrid Supercapacitor Based on Carbon-coated NaTi₂(PO₄)₃ and Activated Carbon Electrode Materials

Anion Exchange Membrane Capacitive Deionization Cells

The electrochemical response of capacitive deionization (CDI) employing a single anion exchange membrane (AEM-CDI) is contrasted to conventional two-membrane CDI (MCDI) formed with complementary anion and cation exchange membranes. Pristine activated carbon cloth electrodes that possess native positive surface charge in solution were used as both anode (positive electrode) and cathode (negative electrode) in these cells. In a separate set of tests to investigate the impact of surface charge modification on deionization responses, the single and dual membrane cells were formed with asymmetric electrodes (AEM-aCDI and aMCDI) consisting of nitric acid oxidized electrodes that possess negative surface charge as the cathode material, while pristine carbon cloth was retained as the anode material. Operating at 1.2 V, salt adsorption capacities are ∼1.3, 9.9, and 16.6, and 17.3 mg NaCl g−1 electrode for the AEM-CDI, MCDI, AEM-aCDI, and aMCDI, respectively. The diminished performance of AEM-CDI is attributed to charge expulsion and enhanced parasitic electrochemical reactions at the unprotected cathode that reduce the charge efficiency. In contrast, for AEM-aCDI, a treated cathode enhances surface charge effects to match aMCDI performance with half the membrane requirement.

Electrochemical Conditioning, Energy Consumption, and Long-Term Performance of Inverted Capacitive Deionization Cells

Capacitive deionization (CDI) can desalinate brackish or lower salt content water at energy costs competitive with reverse osmosis [1]. The brief lifetime of CDI anodes has recently been overcome by operating in an inverted CDI mode (i-CDI), whereby chemical surface charges adsorb ions and an applied potential is subsequently used to repel them to form a concentrated stream [2]. The work here presents new insights on these next generation CDI cells with a focus on in situ anode pre-treatments, energy use, and system longevity for practical considerations. Electrochemically conditioning pristine anodes for 12 hours at +2.5 V was performed in a water stream, i.e. in situ, and immediately deliver peak salt capacities of approximately 6 mg g-1 for SpectraCarb activated carbon cloth electrodes in i-CDI mode (see conditions in Fig. 1). This is in contrast to common ex situ anode pretreatment methods using chemical oxidation in HNO3, which can require lengthy immersion durations, extensive neutralization, and up to 50 cycles (100 h) to reach a similar salt capacity (Fig. 1). This new electrochemical conditioning method can thus save days of processing time to attain steady desalination performance compared to the chemical pretreatment of electrodes and limit the volume of waste stream produced from the treatment process. Moreover, the charge efficiency of electrochemically prepared i-CDI cells is superior to chemical treatment until convergence after 80 cycles. Energy consumption of the cells reaches a minimum of 0.21 kWh m-3, which is approximately 80% lower than reverse osmosis at the feed concentration used here, and approaches the expected energy consumption by CDI desalination [1]. The long-term experiments shown in Figure 1 are run from feed tanks that are not purged of dissolved oxygen in order to more accurately simulate real-world operation. This gives rise to an observed accelerated performance loss with time, independent of the electrode pre-treatment method used. Surface area and sheet resistance measurements suggest that anode degradation (or further oxidation) may be responsible for the decline in performance: anode resistance (HNO3-treated) increased from 60 Ω □-1 before cycling to 600 Ω □-1 after cycling while specific surface area declined from 1390 to 1050 m2 g-1. Frequently, during capacitive deionization experiments, anode degradation is obscured or delayed by the use of membranes, by desalinating for only several cycles, and/or by purging the influent water stream of dissolved O2 with an inert gas such as nitrogen. While these controlled conditions have unveiled critical insights and allowed CDI to flourish in the recent literature, steady performance decline due to anode chemistry may continue to stall commercial adoption, and strategies to mitigate anode oxidation will be reviewed. Figure 1. Long-term salt adsorption capacity and charge efficiency for i-CDI cells operated at +0.8/0 V after electrochemical and nitric acid anode pre-treatments; 4.5 mM NaCl solution was circulated at 20 ml min-1 in single-pass mode through 3.5 g of SpectraCarb electrodes. [1] Oren Y. Capacitive delonization (CDI) for desalination and water treatment - past, present and future (a review). Desalination 2008;228:10-29. [2] Gao X, Omosebi A, Landon J, Liu KL. Surface charge enhanced carbon electrodes for stable and efficient capacitive deionization using inverted adsorption-desorption behavior. Energ Environ Sci 2015;8:897-909. Acknowledgements These authors are grateful to the U.S.-China Clean Energy Research Center, U.S. Department of Energy (DE-PI0000017) for project funding. Figure 1

Complementary surface charge for enhanced capacitive deionization

Commercially available activated carbon cloth electrodes are treated using nitric acid and ethylenediamine solutions, resulting in chemical surface charge enhanced carbon electrodes for capacitive deionization (CDI) applications. Surface charge enhanced electrodes are then configured in a CDI cell to examine their salt removal at a fixed charging voltage and both reduced and opposite polarity discharge voltages, and subsequently compared to the salt removal of untreated electrodes. Substantially improved salt removal due to chemical surface charge and the use of a discharge voltage of opposite sign to the charging voltage is clearly demonstrated in these CDI cycling tests, an observation which for the first time validates both enhanced CDI and extended-voltage CDI effects predicted by the Donnan model [Biesheuvel et al., Colloids Interf. Sci. Comm., 10.1016/j.colcom.2015.12.001 (2016)]. Our experimental and theoretical results demonstrate that the use of carbon electrodes with optimized chemical surface charge can extend the CDI working voltage window through discharge voltages of opposite sign to the charging voltage, which can significantly enhance the salt adsorption capacity of CDI electrodes. Thus, in addition to carbon pore size distribution, chemical surface charge in carbon micropores is considered foundational for salt removal in CDI cells.