Graphene-like Carbon Sheets Research Articles

Understanding Electrochemical Growth of Carbon Nanotubes from CO2

Previous works have pioneered the observation of carbon nanotube growth in molten LiCO3 electrolytes from CO2. However in many past works, several CO2-derived cathodic carbon morphologies were observed, which included carbon particles/spheres, graphite flakes, carbon nanofibers, CNTs, and graphene-like ultrathin carbon sheets. Moreover, these morphologies are often mixed, resulting in a low selectivity and difficult separation towards one single carbon morphology, and the factors leading to various morphologies are not currently well understood. In this talk, we will explore the fundamental growth mechanism to inform the broader long-term goal of improving the selectivity towards carbon nanotubes from CO2. This present work studied the cathodic growth of carbon nanotubes by utilizing a simple three-electrode configuration consisting of pure Li2CO3 electrolyte, pure transition metal foil cathodes, Pt anode, and homemade Ag/Ag2SO4 reference electrode to determine the impact of tunable parameters on the resulting electroreduction products.

Fe3C-Decorated Folic Acid-Derived Graphene-like Carbon-Modified Separator as a Polysulfide Barrier for High-Performance Lithium-Sulfur Batteries

The lithium-sulfur (Li-S) battery has been regarded as an important candidate for the next-generation energy storage system due to its high theoretical capacity (1675 mAh g−1) and high energy density (2600 Wh kg−1). However, the shuttle effect of polysulfide seriously affects the cycling stability of the Li-S battery. Here, a novel Fe3C-decorated folic acid-derived graphene-like N-doped carbon sheet (Fe3C@N-CS) was successfully prepared as the polysulfide catalyst to modify the separator of Li-S batteries. The porous layered structures can successfully capture polysulfide as a physical barrier and the encapsulated Fe3C catalyst can effectively trap and catalyze the conversion of polysulfide, thus accelerating the redox reaction kinetics. Together with the highly conductive networks, a cell with the Fe3C@N-CS-modified separator evinces superior cycling stability with 0.06% capacity decay per cycle at 1 C rate over 500 cycles and excellent specific capacity with an initial capacity of 1260 mAh g−1 at 0.2 C. Furthermore, at a high sulfur loading of 4.0 mg cm−2, the batteries also express superb cycle stability and rate performance.

High-voltage aqueous symmetric supercapacitors based on 3D bicontinuous, highly wrinkled, N-doped porous graphene-like ultrathin carbon sheets

Biomass-derived 3D bicontinuous, highly-wrinkled, N-doped porous graphene-like ultrathin carbon sheets for high-performance aqueous symmetric supercapacitor.

Structural Evaluation of Coal-Tar-Pitch-Based Carbon Materials and Their Na+ Storage Properties

Linking to the S element hybrid strategies, S-doped carbon materials having different macrostructures and defect concentrations are prepared by using sulfur and coal-tar-pitch as raw materials in a carbonization temperature range of 700–1000 °C. The evaluations of macrostructure and surface characteristics are performed through XRD, TEM, Raman and XPS measurements. Through the linear fitting among the Na+ storage capacity with ID/IG and d002 values, the correlations of Na+ storage capacity with macrostructures and defects are respectively investigated in detail. It is observed that S-doped carbon materials exhibit storage capacity at 120 mAh/g after the charge-discharge is being carried out 2000 cycles at 2.0 A/g. Studies have shown that adsorptions of introduced defects on graphene-like carbon sheets mainly play the role to enhance the storage capacity, and the expanded carbonaceous lamellar spaces of highly disordered and pseudo-graphitic macrostructures provide the channels for fast transfer of Na+. Our studies are able to provide references for designs and fabrications of coal tar pitch based soft carbon materials as sodium-ion batteries (SIBs) anodes when using heteroatoms doping methods.

Single-step synthesis of N, S co-doped waste-derived nanoporous carbon sorbent for mercury vapor removal.

As well known, mercury is a toxic trace element due to its bioaccumulation and volatility which results in severe effects in health of ecosystems and humans' life. Herein, for the first time, the synthesis of a N and S dual-doped waste-derived graphene-like nanoporous carbon via a facile and single-step route is presented and its capability in mercury vapor removal from gas streams is investigated. To prepare a modified adsorbent, thiourea was utilized as the doping agent to induce nitrogen and sulfur dopants into the nanoporous carbon structure derived from pyrolysis of cabbage (Capitat. var. Brassica oleracea) waste from Brassicaceae family as an inherently S, N-containing precursor, which is produced in noticeable amounts annually. The prepared adsorbents were characterized through FTIR, XRD, BET, SEM, TEM, and CHNOS techniques to get an insight into the structure, morphology, and chemical characteristics of the adsorbents. The structural characterization revealed the successful synthesis of a graphene-like nanoporous carbon sheet which was doped with nitrogen and sulfur atoms. The S, N dual-doped graphene-like carbon nanosheets showed an enhanced activity toward mercury vapor adsorption. For this end, two different dopant to carbon source ratios were considered and it was found that the higher dopant amount results in a better performance. From the adsorption experiments, it was revealed that the pristine graphene-like carbon had a less performance in mercury removal (71%) compared with doped samples (more than 90%) which shows the necessity of reinforcement and surface modification of as mentioned cabbage base graphene. However, the best sample which was prepared with the dopant to carbon ratio of 10 had a performance of 94.5% removal (2100μg/g) compared with 89% (1980μg/g) for mercury removal by the sulfur-impregnated commercial activated carbon.

Graphene-like carbon sheet-supported nZVI for efficient atrazine oxidation degradation by persulfate activation

Developing excellent carrier materials for supporting metal-based catalysts is challenging. Herein, a graphene-like carbon sheet (CS) was fabricated from a mixture of corn straw and potassium oxalate (K2C2O4) via a simple one-pot approach. The as-obtained sample possesses a 2D lamellar structure similar to graphene, which improves the specific surface area of the biochar. CS-supported nanoscale zero-valent iron (nZVI) composites (nZVI@CS) were designed to enhance atrazine removal by persulfate (PS) activation. The removal efficiencies of nZVI@CS-800 were higher than that of nZVI-PS, implying that the synergy between CS and nZVI was achieved and promoted the removal efficiency of atrazine. CS facilitates the dispersion of nZVI due to its vast SSA, which could prevent nZVI particles from self-aggregation. Simultaneously, the degradation may be by preferentially degrading the atrazine adsorbed on catalyst to promote adsorption. SO4− plays a more important role in the oxidative degradation of atrazine. CS can directly activate PS to generate SO4−, and as an electron shuttle, it can promote the conversion of Fe3+ to Fe2+ and improve the activity of the catalyst. The apparent mineralization rate of atrazine after reaction for 60 min is 38.65%, and degradation pathways include dealkylation, alkyl oxidation and dichlorination. Oxidative degradation of atrazine is favored at high temperature or low pH, while it is inhibited when the amount of PS or catalyst becomes excessive. And it may be impacted by organic compounds or anions in the environment. This study is of great significance for the practical application of nZVI@CS for in situ organic pollution remediation.

Synthesis of graphene-like carbon from agricultural side stream with magnesiothermic reduction coupled with atmospheric pressure induction annealing

Generally, large-scale production of graphene is currently not commercially viable due to expensive raw materials, complexity and the high-energy consumption of the processes currently used in the production. The use of biomass precursors and energy efficient procedures for carbonization have been proposed to reduce the cost of the graphene materials. However, low-cost graphene production has not been accomplished yet. Herein, we present a sustainable procedure and renewable starting materials to synthesize carbon nanostructures with graphene-like features. First, a SiC/C composite was synthesized from phytoliths and sucrose through magnesiothermic reduction. The phytoliths were obtained from barley husk that is an abundant side stream of agricultural industry. Second, graphene-like structures were achieved by the graphitization of SiC/C composite with high temperature induction annealing at 2400 °C under atmospheric pressure. The formation of graphene-like carbon was initiated by vaporization of silicon from the pre-ceramic SiC/C. Complete transformation of SiC/C to hollow, spherical graphene-like carbon structures and sheets were verified with thermogravimetry, x-ray diffraction, energy dispersive spectroscopy, electron microscopy and Raman spectroscopy. Also, the theoretical thermodynamic consideration of the phase separation of silicon carbide and the role of free carbon in the process has been discussed.

Predicting whether aromatic molecules would prefer to enter a carbon nanotube: A density functional theory study

The interaction of a carbon nanotube (CNT) with various aromatic molecules, such as aniline, benzophenone, and diphenylamine, was studied using density functional theory able to compute intermolecular weak interactions (B3LYP-D3). CNTs of varying lengths were used, such as 4-CNT, 6-CNT, and 8-CNT (the numbers denoting relative lengths), with the lengths being chosen appropriately to save computation times. All aromatic molecules were found to exhibit strong intermolecular binding energies with the inner surface of the CNT, rather than the outer surface. Hydrogen bonding between two aromatic molecules that include N and O atoms is shown to further stabilize the intermolecular adsorption process. Therefore, when benzophenone and diphenylamine were simultaneously allowed to interact with a CNT, the aromatic molecules were expected to preferably enter the CNT. Furthermore, additional calculations of the intermolecular adsorption energy for aniline adsorbed on a graphene surface showed that the concavity of graphene-like carbon sheet is in proportion to the intermolecular binding energy between the graphene-like carbon sheet and the aromatic molecule.

Defect-Rich, Graphenelike Carbon Sheets Derived from Biomass as Efficient Electrocatalysts for Rechargeable Zinc–Air Batteries

Rechargeable Zinc–air batteries (RZABs) have attracted much attention due to their low cost, environmental benignity, high safety, and specific energy density. The bottleneck blocking the large-sca...

Graphene like Porous Carbon Sheets Derived from Hibiscus Cannabinus As a Versatile Electrochemical Energy Storage Material

In recent years, energy storage devices such as supercapacitors (SC) and Li-ion batteries (LIB) have attracted worldwide interest due to their critical role in replacing the conventional fuels in the transportation sector and also owing to their promising electro-chemical characteristics like long cycle life, high energy density, high power density and low toxicity [1]. In LIBs and SCs, carbon electrode material is arguably an important component and plays a pivotal role in the device performance. However, development of low cost carbon electrode materials with improved energy density and long cycle stability are the great challenges to meet the increasing demands of upcoming electric vehicle technology. Various carbon materials, such as activated carbon, mesoporous carbon, graphene and carbon nanotubes have been extensively studied as electrode materials. However, there are certain limitations using these materials for commercial applications due to their inappropriate pore structure, high cost, tedious synthesis conditions etc. [2]. Graphene-like porous carbon sheets (GPCSs) have recently been viewed as the outstanding electrode materials for high rate electrochemical storage devices such as supercapacitors and Li-ion batteries because the 2D porous carbon sheets can integrate the high conductivity as well as high porosity to promote the facile diffusion of both ion transport and electron transfer. Herein, synthesizing graphene like porous carbon sheets from a renewable biomass waste (Hibiscus cannabinus sticks) is of great importance in lowering the production costs and also promoting environmental protection. The relationship between structure of the GPCS-X (X represents the concentration of activation agent) and its electrochemical performance at different concentration of activating agent is explored in detail. The resulting porous carbon sheets possesses excellent textural parameters with a high specific surface area of 2308 m2/g, highly ordered graphitic carbon with a ID/IG ratio of 0.315 which is confirmed by BET, Raman, HR-TEM (Figure 1a and 1b) etc. While being used as supercapacitor application, the GPCS electrode exhibits a high specific capacitance of 240 F/g at 1A/g, excellent rate capability (84% capacity retention at 50 A/g) and also shows outstanding cyclic stability (92% capacitance retention after 25,000 cycles) in aqueous electrolyte. When tested in organic electrolyte with an extended voltage window, the electrode exhibits symmetric charge-discharge profiles as shown in figure 1c. Also, for Li-ion battery application, GPCS electrode material as shown in figure in 1d displayed a high reversible capacity (1050 mAh/g at 100 mA/g), excellent rate performance (230 mAh/g at 5000 mA/g), and good cycling stability (72% capacitance retention after 400 cycles). The excellent electrochemical performance of GPCS electrode material can be attributed to the high electrical conductivity of the graphene network along with high specific surface area. These results demonstrate a facile, low-cost, eco-friendly design of electrode materials for energy storage applications. Figure 1 (a) FE-SEM and (b) HR-TEM images of GPCS material (c) Charge-Discharge profiles for Supercapacitor application and (d) Rate comparison for Li-ion battery application.

Point-Defect-Rich Carbon Sheets as the High-Activity Catalyst Toward Oxygen Reduction and Hydrogen Evolution

Exploring a novel approach for the synthesis of oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) catalysts with inexpensive and high-activity is desirable. Herein, we report a bubble templating method to synthesize the graphene-like mesoporous carbon sheets with point defects as ORR/HER bifunctional electrocatalysts. The typical product shows excellent ORR performance including the positive onset potential (740 mV) and high diffusion-limiting current density (4.07 mA cm−2). Along with small Tafel slopes, the overpotential is determined to be about −453 and −378 mV at 10 mA cm−2 in both alkaline and acidic media, which suggests a good candidate for HER reaction as well. The superior catalytic activities are derived from the abundant point defects on the mesoporous carbon sheets surface, especially the existence of pyridinic and pyrrolic nitrogen species. This study may be an alternative route to prepare the novel functional materials for the applications of ORR and HER.

Nickel loaded graphene-like carbon sheets an improved electrocatalyst for hydrogen evolution reaction

Abstract In this article, we successfully prepare Ni loaded graphene-like carbon sheets which act as an efficient electrocatalyst for hydrogen evolution reaction. The as-prepared electrocatalysts show an ultrathin rose petal-like carbon sheets structure loaded with micro and nano-sized Ni particles. The electrocatalytic activity of Ni loaded carbon sheets electrocatalysts are studied in 1 M KOH solution. Ni-GCS-2 shows overpotential of 0.205 V (vs RHE) at a current density of 10 mA cm−2 with better stability for 4 h continuously and lower Rct. Ni-GCS-2 shows only 15% loss for HER after 4 h. The effect of Ni on electrocatalytic performance was investigated. The Ni Nano particles are the active sites for the reaction and graphene-like carbon sheets facilitate electron transport due to their conductive nature. This study showed that Ni-GCS-2 is better in performance as compared to other as-prepared electrocatalyst and previously studied Ni-based electrocatalysts.

Nitrogen and sulfur co-doped graphene-like carbon sheets derived from coir pith bio-waste for symmetric supercapacitor applications

An efficient synthesis of nitrogen and sulfur co-doped graphene-like carbon sheets from coir pith bio-waste through the mechanical activation method is reported in this study. The structural characterization reveals the presence of a graphene-like carbon sheet, which is uniformly doped with nitrogen and sulfur atoms in a carbon network. The nitrogen and sulfur co-doped graphene-like carbon sheets (NSG) has amorphous nature with a defective porous carbon structure and it depicts the maximum specific capacitance of 247.1 F g−1 at 0.2 A g−1 and a capacitance retention of 75.2% at 10 A g−1. The synthesized NSG-10 registered a maximum energy density of 33.6 Wh kg−1 at 0.2 A g−1 and shows the maximum power density of 4220.0 W kg−1 at 10.0 A g−1. Furthermore, a symmetric supercapacitor (SSC) device shows the device capacitance of 33.7 F g−1 at 0.2 A g−1 when operated at 1.0 V. The SSC device gives a capacitance retention of 82.0% at 10 A g−1 and reveals an excellent stability with no losses in capacitance with 100% columbic efficiency over 10,000 cycles. The results suggest that the proposed methodology is a simple and unique way to synthesize heteroatoms-doped graphene-like carbon sheets from biomass materials for a supercapacitor.

One-pot self-assembly of sisal-like TiO2 on graphene-like carbon sheets via a novel two-phase interface-facilitated route

A Sisal-Like TiO2/Graphene-Like Carbon Sheets (SL-TiO2/GLCSs) composite was fabricated via a facile one-pot self-assembling route at a two-phase interface. The ingenious P123 was introduced to serve a dual function of carbon precursor and structure-directing agent, which first assembled at the water/oil interfaces and subsequently was in situ carbonized to GLCSs. Then the sisal-like TiO2 grew gradually on the GLCSs along the preferred direction. This process shows several advantages such as simple processes, mild condition, low cost and good combination of SL-TiO2 and GLCSs. The combination of SL-TiO2 with GLCSs significantly helps the adsorption of substrates as well as promotes electron-hole pair separation, exhibiting good photocatalytic activity towards degradation of methylene blue (MB) compared to the pristine SL-TiO2 and commercial P25. This strategy opens up new perspectives for fabricating novel composites of nanooxides/GLCSs.

Increased activity of nitrogen-doped graphene-like carbon sheets modified by iron doping for oxygen reduction

Rational design and synthesis of Fe-N-codoped carbon materials are promising for replacing commercial Pt/C for oxygen reduction reaction (ORR). Herein, we develop a simple two-step pyrolysis approach to synthesize highly active Fe-N-codoped graphene-like carbon sheets (FeNGC) with active Fe-N-based species for ORR. In this strategy, two-dimensional nitrogen-doped graphene-like carbon sheets (NGC) with a high N-doping level (8.1 at%) and abundant mesoporosity (3.8 nm) are firstly synthesized by co-pyrolysis of biomass carbon source and dicyandiamide, in which dicyandiamide simultaneously serves as a trifunctional role of in situ reaction template, nitrogen source and porogen. Secondly, FeNGCs are prepared by additional iron doping of NGC at high temperatures, in which sheet-like structure is in favor of increased accessibility of N-functional groups to more Fe atoms, thus giving rise to formation of high-density Fe-N-based active sites. The optimized catalyst synthesized at 950 °C (FeNGC-950) demonstrates significantly increased ORR activity with a dominant 4e− reduction process compared to pure NGC in alkaline and acidic solutions, which evidently shows the comparable activity to Pt/C due to the synergy of simultaneously optimized structures and multi-active sites. Moreover, FeNGC-950 has better long-term stability and methanol tolerance than Pt/C both in alkaline and acidic electrolytes. The present strategy paves a new venue to design and prepare various metal-doped carbon materials with great potentials in energy applications.

On the carrier phase of the “planetary” noble gases: TEM, Raman, and stepped combustion data for acid-resistant residues from the Saratov (L4) meteorite

Acid-resistant residues (ARR) were separated from the Saratov (L4) meteorite with the aim to shed more light on the origin of the planetary noble gases (the Q-gases) in meteorites and the nature of their carrier phase (Q-phase). Eleven fractions were obtained by HCl and HCl+HF etching, ultrasonication, and subsequent density separation of the ARR in isopropanol and isopropanol+NaOH. Two aliquots of the fractions were also treated with H2O2 and HNO3 to investigate any influence of the oxidizing agent on the Q-gases retention. The separated ARR fractions have been analyzed for C, N, and noble gases using step combustion. Raman and TEM analyses of the carbonaceous phase structures have also been applied for some of the fractions. This appears to be one of the most detailed investigations of the ARR fractions so far. The important observation made for the ARR fraction studied by TEM is the presence of abundant curved graphene stacks with a variable number of layers. Significant amounts of single- and bilayer graphenes and nanosized chromite grains partly covered with graphene layers are also observed. The principal features of the Q noble gases in the studied ARR fractions are the following. (1) Elemental composition of the Q-gases depends on the extraction protocol. The most interesting is that upon H2O2 oxidation, the noble gases are retained in the sequence Xe<Ar≪He, while after HNO3 it is in the sequence He≪Xe<Ar. (2) The resistance of the Q-phase against the thermochemical treatment is lower than for the graphite-like phase. The results of the current work together with literature data suggest that nongraphitizing curved graphene-like carbon sheets are the most plausible carrier of the Q-gases.

Carbon nitride template-directed fabrication of nitrogen-rich porous graphene-like carbon for high performance supercapacitors

Facile yet rationally designed strategy for advanced electrode material synthesis is pivotal for energy storage. Herein, we report an protocol for g-C3N4 template-directed in-situ fabricating nitrogen-rich porous graphene-like carbon sheets (NPGCs) by using plasma-enhanced chemical vapor deposition followed with high-temperature pyrolysis process, which totally avoids the postsynthetic template-removal. The resultant NPGCs integrate a range of intriguing features including highly conductive interconnected structure (693 S m−1), abundant mesoporous with ultrahigh pore volume (4.35 cm3 g−1), large specific surface area (1277 m2 g−1), high N doping (8.75 wt%), and good wettability. As supercapacitor electrode, the NPGCs exhibit a quite encouraging specific capacitance of 261 F g−1 at 1 A g−1, excellent rate capability (189 F g−1 even at 100 A g−1), and outstanding cycle performance (97% capacitance retention at 10 A g−1 after 20000 cycles), which outperforms most carbon-based materials reported to date. Moreover, the assembled supercapacitors deliver a high power density of 28.4 kW kg−1 with a energy density of 6.53 Wh kg−1 at 100 A g−1. Our work is expected to open up new avenues for developing efficient nitrogen-doped porous carbon materials in a facile and viable way.

Harvesting a 3D N-Doped Carbon Network from Waste Bean Dregs by Ionothermal Carbonization as an Electrocatalyst for an Oxygen Reduction Reaction.

Three-dimensional nitrogen-doped carbon (3D-NCN) has been synthesized via the ionothermal carbonization method using waste soybean dregs (SD) as the precursor. N2 adsorption/desorption isotherms show that the as-prepared 3D-NCN formed a hierarchically porous structure with a specific BET surface area of 1093.4 m2 g−1 and a total pore volume of 1.77 cm3 g−1. The TEM images clearly show that graphene-like carbon sheets were formed on the edge of the networks. The characterization of the samples collected at different temperature indicated that salt melt plays the key role in the formation of the network structure and rich pores. When 3D-NCN is as electrocatalyst for ORR, it shows an onset potential of 0.945 V with a more positive half-wave potential (0.846 V), which is comparable to that of commercial Pt/C. In addition, the long-term cycle results show that the onset potential and half-wave potential only negatively shifted by 6 mV and 8 mV after 10,000 cycles respectively, which are smaller than those values of commercial Pt/C. Due to its high ORR activity, durability, and low-cost, producing 3D-NCN from SD in molten salt medium provides a promising approach to replace the Pt-based catalysts for use in fuel cells.

New insights into bisphenols removal by nitrogen-rich nanocarbons: Synergistic effect between adsorption and oxidative degradation

In this work, nitrogen-rich graphene-like carbon sheets (N-GLCS) with high specific surface area (488.4m2/g), narrow pore distribution and high N-doping (18.4 at%) were prepared and applied as both adsorbent and catalyst for the removal of bisphenols. Adsorption experiments demonstrated the high adsorption capacities of the N-GLCS toward bisphenol F (BPF) (222.9mg/g), bisphenol A (BPA) (317.8mg/g), and bisphenol C (BPC) (540.4mg/g). Results showed that about 98.6% of BPA (70mg/L) was removed at pH 7.0 within 80min after the adsorption-catalytic degradation process. The N-GLCS also showed a superb reusability for the catalytic oxidative degradation of BPA (70mg/L) with the removal percentage maintains over 83% after 5 cycles. With the synergistic combination of the excellent adsorption and catalytic properties of the N-GLCS, trace amount of pollutants can be preconcentrated and immobilized at the surface of N-GLCs, at the same time, active radicals were also produced at the surface of the N-GLCS by the activation of peroxydisulfate (PS), and finally the pollutants can be degraded in-situ by the active radicals. These findings provide a new avenue towards the efficient removal of trace-level EDCs from water solution by using the coupled adsorption-advanced oxidation processes.

Graphene-like carbon sheet/Fe3O4 nanocomposites derived from soda papermaking black liquor for high performance lithium ion batteries

Alkali lignins and its degradation products in the soda papermaking black liquor (SPBL) are renewable resource with the highest natural carbon content. In this work we convert SPBL into the high-performance carbon-based nanocomposite anodes. The unique functional groups of lignin biomass induce spontaneous formation of graphene-like carbon sheet (GCS) in-situ doped SiC/S. The lamellar GCS/Fe3O4 nanocomposite (GCS/FO-NC) is facilely prepared via one-step in-situ thermo-chemical method at 700°C, in which donut shaped Fe3O4 nanoparticles with superlattices and inner surface are homogeneously embedded in the interlayer of GCS and are also anchored on its surface. The GCS/FO-NC anode exhibits a ultrahigh first discharge specific capacity of 3829mAhg−1 at 50mAg−1 in a coin-type Li ion battery, which is more than 4 times the theoretical capacity (924mAhg−1) of Fe3O4 and 5 times that of the graphene anode (744mAh. g−1). Even at a high current density (1000mAg−1), it still exhibits a high reversible capacity (750mAhg−1) after 1400 discharge/charge cycles. More importantly, the removal efficiency of chemical oxygen demand of SPBL is up to 83.4% during the synthesis process, which reduce its load to environment and synthetic cost of carbon-based nanocomposite anodes.