Anode Area Research Articles

Treatment of the Lead Waste Water with Electrochemical Process

Industrial waste water with high levels of lead has serious threat to human health and other organisms. Power generation methods were used for recycling of lead. Some factors such as temperature,power generation time,the anode material, type and concentration of anode area solution on the power generation process were studied to find the optimal process parameters.The experimental results show that:in the optimum conditions,the recovery rate of lead was more than 90% and the lead concentration in waste water has reached the discharge standard. This method does not produce by-products of environmental pollution in the power generation process and needn’t external supply of energy but produce certain energy. So it is a green chemistry technology.

Ruthenium oxide-coated carbon felt electrode: A highly active anode for microbial fuel cell applications

Enhancing the anode performance is a critical step for improving the power output of microbial fuel cells (MFCs). This study presents an active anode that involves the use of ruthenium oxide (RuO2)-coated carbon felt electrode for MFC applications. Cathodic electrodeposition was performed to decorate the carbon felt surface with the RuO2 films composed of submicron-/nano-sized particles. Increasing the amount of charge applied for the electrodeposition resulted in the increase in power performance of MFCs that were inoculated either with the pure culture or the mixed microbial consortia. The dual-chamber MFC equipped with the RuO2-coated anode reached the maximum power density of 3.08Wm−2 (normalized to the projected area of anode), increased by 17 times as compared to that obtained with the MFC with the bare anode. Cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) results provided evidence that there was a substantial improvement in electron transfer between the microbes and the anode. The results demonstrate that RuO2 interacts electrochemically with the cells and has ability to facilitate extracellular electron transfer.

Influence of NaCl, Na2SO4 and O2 on power generation from microbial fuel cells with non-catalyzed carbon electrodes and natural inocula

Microbial fuel cells (MFCs) are facing several technological challenges before they can be considered as reliable energy sources. Although several feasible inocula, materials and catalysts have been employed to produce energy, the design of a MFC should be done under realistic conditions: abundant and economic feedstock. In this study, two different MFC designs (parallel plate and tank reactors) are tested with non-catalyzed carbon electrodes and natural inocula. In both approaches cathodic oxygen reduction is performed on two different non-catalyzed carbon materials: carbon fabric and reticulate vitreous carbon. This study shows that power and current densities can be boosted by systematically decreasing the catholyte resistance (by additions of NaCl or Na2SO4) and dissolved oxygen concentration. In the parallel plate cell configuration, a mixed culture coming from sludge wastewater was used and power outputs up to 73mWm−2 (2867mWm−3) coupled to 187mAm−2 (anode surface area), were achieved. In the Sediment MFC cell configuration, lagoon sediment was used as both organic source of energy and natural supply of bacteria. Under this approach, the concentration of the organic matter is limited but it is demonstrated that bacteria can be adapted to degrade acetate. Power outputs up to 3.9mWm−2 normalized to the anodic electrode footprint area, coupled to 13mAm−2 were achieved.

Revealing the mechanism of indirect ammonia electrooxidation

The governing mechanism of indirect ammonia electrooxidation has been often described similarly to breakpoint chlorination. However, comparison of the chloramine concentrations which develop in batch indirect ammonia electrolysis and classical breakpoint chlorination experiments (performed under similar conditions) suggests that the governing reactions are different. Three experimental sets were carried out with excess-ammonia solutions, with the aim of elucidating the mechanism of indirect electrochemical ammonia oxidation: (1) chloramination with Cl2(g) and NaOCl; (2) batch- and (3) single-pass electrolysis experiments.Based on the results we propose a new mechanism for indirect ammonia electrooxidation, according to which trichloramine, rather than monochloramine, is the initial and primary product. NCl3 apparently forms from a reaction between NH4+ and Cl2(aq), which occurs in the near anode area where pH is <2 and the bulk Cl− concentration is high. At such conditions Cl2(aq) is the dominant active chlorine species in the anode vicinity. Upon formation in the near anode area NCl3 decomposes to N2, NH2Cl and NHCl2 in the bulk solution or/and close to the cathode surface area, where pH>12. Under batch operation and/or single-pass electrolysis characterized by long contact times both NH2Cl and NHCl2 that form in the bulk electrolyte are oxidized to NCl3 by Cl2(aq) upon return to the near-anode zone.

Potential distribution characteristics of mild steel in seawater

Potential distribution of mild steel immersed in seawater for various periods was investigated by SMRE (scanning micro-reference electrode). For the coupons immersed horizontally, the edge was cathode while the middle was anode. When immersed vertically, the top of the coupon was the main cathode. After a period of immersion, the bottom became the main cathode. No matter how the coupons were placed, the composition of corrosion products in the cathodic area was β-FeOOH and Fe3O4 while in the anodic area was mainly γ-FeOOH. Relationship between potential distribution and corrosion products was discussed and the reasons for this phenomenon were analysed.

Power generation from wastewater using single chamber microbial fuel cells (MFCs) with platinum-free cathodes and pre-colonized anodes

The effects of biofilm growth on anode and cathode surfaces on the power generation from wastewater in single chamber microbial fuel cells (SCMFCs) were investigated in this paper. SCMFCs with the clean/pre-colonized anodes and the platinum-based/platinum-free cathodes were operated for 26 weeks. The pre-colonized (4-week colonization) anodes were tested with three areas (2, 10 and 40cm2) and compared with the MFCs started with clean and sterilized anodes. The power generation of MFCs increased with the anode areas (2–10cm2), but kept a plateau for the anode area of 40cm2. The MFCs with the clean anodes had lower power generation (268mW/m2) than those with the pre-colonized anodes (801mW/m2) in the first week of operation. With the operation proceeding to 4–5 weeks, the power generation of the clean anodes and pre-colonized anodes became similar and stabilized at 470mW/m2. In terms of cathode performance, platinum-free cathodes (carbon cloth, surface area: 5cm2) and platinum-based cathodes (Pt loading: 0.5mgPt/cm2, surface area: 5cm2) were compared. The Pt-based cathodes had higher power generation (330mW/m2) than those of the Pt-free cathodes (253mW/m2) at the startup period, but the difference quickly vanished after a few weeks of operation. This study demonstrated that the advantage of the MFCs with the pre-colonized anodes and platinum-based cathodes disappeared after 3–5 weeks of operation due to the thick biofilm growth on anodes and the aerobic biofilm formation on cathodes. Pt-free cathodes with controlled biofilm growth are promising for low-cost materials, stable power generation and long-term operation of MFCs.

Hydrazine/air direct-liquid fuel cell based on nanostructured copper anodes

Fuel cells (FCs) are promising electrochemical devices that convert the chemical energy of fuels directly into electrical energy, as long as the fuel is supplied.This paper describes a room-temperature hydrazine/air direct-liquid fuel cell (DLFC) based on the use of nanostructured copper electrodes. We show that nanostructured copper electrodes function as highly efficient and ultra-long-lasting catalyst for the electro-oxidation of hydrazine. Our Cu/hydrazine anodes show high electrical efficiency for long periods of continuous operation (more than 500h).A hydrazine/air fuel cell prototype was built with a nanostructured Cu/hydrazine anode, combined with a commercial air cathode. The output of this cell is about 0.45W at 1A (0.1Acm−2 corresponds to the anode area), and supplies about 2.3Wh and 1300Whkg−1 hydrazine. The hydrazine discharge efficiency is higher than 85%.

Arsenic-Doped High-Resistivity-Silicon Epitaxial Layers for Integrating Low-Capacitance Diodes.

An arsenic doping technique for depositing up to 40-μm-thick high-resistivity layers is presented for fabricating diodes with low RC constants that can be integrated in closely-packed configurations. The doping of the as-grown epi-layers is controlled down to 5 × 1011 cm−3, a value that is solely limited by the cleanness of the epitaxial reactor chamber. To ensure such a low doping concentration, first an As-doped Si seed layer is grown with a concentration of 1016 to 1017 cm−3, after which the dopant gas arsine is turned off and a thick lightly-doped epi-layer is deposited. The final doping in the thick epi-layer relies on the segregation and incorporation of As from the seed layer, and it also depends on the final thickness of the layer, and the exact growth cycles. The obtained epi-layers exhibit a low density of stacking faults, an over-the-wafer doping uniformity of 3.6%, and a lifetime of generated carriers of more than 2.5 ms. Furthermore, the implementation of a segmented photodiode electron detector is demonstrated, featuring a 30 pF capacitance and a 90 Ω series resistance for a 7.6 mm2 anode area.

Response of reinforced concrete structures to macrocell corrosion of reinforcements. Part I: Before propagation of microcracks via an analytical approach

Assessment of the macrocell corrosion which deteriorates reinforced concrete (RC) structures have attracted the attention of many researchers during recent years. In this type of rebar corrosion, the reduction in cross-section of the rebar is significantly accelerated due to the large ratio of the cathode's area to the anode's area. In order to examine the problem, an analytical solution is proposed for prediction of the response of the RC structure from the time of steel depassivation to the stage just prior to the onset of microcrack propagation. To this end, a circular cylindrical RC member under axisymmetric macrocell corrosion of the reinforcement is considered. Both cases of the symmetric and asymmetric rebar corrosion along the length of the anode zone are studied. According to the experimentally observed data, corrosion products are modeled as a thin layer with a nonlinear stress–strain relation. The exact expressions of the elastic fields associated with the steel, and concrete media are obtained using Love's potential function. By imposing the boundary conditions, the resulting set of nonlinear equations are solved in each time step by Newton's method. The effects of the key parameters which have dominating role in the time of the onset of concrete cracking and maximum radial stress field of the concrete have been examined.

Response of reinforced concrete structures to macrocell corrosion of reinforcements. Part II: After propagation of microcracks via a numerical approach

Abstract Investigation of response of reinforced concrete (RC) structures due to axisymmetric macrocell corrosion of rebars is of concern after propagation of microcracks within the concrete medium. The geometry, boundary and interfaces conditions of the present problem are identical to those stated in part I. As seen in the companion paper, the exact solution to the boundary value problem corresponding to the uncracked steel–rust–concrete composite was possible. After appearance of the microcracks the concrete behavior becomes nonlinear anisotropic with post-cracking softening, and the associated problem is analytically intractable. Therefore, it is proposed to employ a novel meshless method, namely gradient reproducing kernel particle (GRKPM), in the cylindrical coordinates. The analytical and numerical solutions pertinent to the uncracked concrete are in good agreement. Subsequently, the effects of the parameters associated with the mechanical behavior of concrete and properties of rust on the time of surface cracking, the maximum values of consumed rebar per unit area of anode and crack width openings at the time of surface cracking, and the maximum value of radial stress at the rust–concrete interface are scrutinized in some detail.

Population dynamics and current-generation mechanisms in cassette-electrode microbial fuel cells

Cassette-electrode microbial fuel cells (CE-MFCs) have been demonstrated useful to treat biomass wastes and recover electric energy from them. In order to reveal electricity-generation mechanisms in CE-MFCs, the present study operated a bench-scale reactor (1 l in capacity; approximately 1,000 cm(2) in anode and cathode areas) for treating a high-strength model organic wastewater (comprised of starch, peptone, and fish extract). Approximately 1 month was needed for the bench reactor to attain a stable performance, after which volumetric maximum power densities persisted between 120 and 150 mW/l throughout the experiment (for over 2 months). Temporal increases in the external resistance were found to induce subsequent increases in power outputs. After electric output became stable, electrolyte and anode were sampled from the reactor for evaluating their current-generation abilities; it was estimated that most of current (over 80%) was generated by microbes in the electrolyte. Cyclic voltammetry of an electrolyte supernatant detected several electron shuttles with different standard redox potentials at high concentrations (equivalent to or more than 100 μM 5-hydroxy-1,4-naphthoquinone). Denaturing gradient gel electrophoresis and quantitative real-time PCR of 16S ribosomal RNA gene fragments showed that bacteria related to the genus Dysgonomonas occurred abundantly in association with the increases in power outputs. These results suggest that mediated electron transfer was the main mechanism for electricity generation in CE-MFC, where high-concentration electron shuttles and Dysgonomonas bacteria played important roles.

Vanadium Oxide Nanowire–Carbon Nanotube Binder‐Free Flexible Electrodes for Supercapacitors

AbstractVanadium pentoxide (V2O5) layered nanostructures are known to have very stable crystal structures and high faradaic activity. The low electronic conductivity of V2O5 greatly limits the application of vanadium oxide as electrode materials and requires combining with conducting materials using binders. It is well known that the organic binders can degrade the overall performance of electrode materials and need carefully controlled compositions. In this study, we develop a simple method for preparing freestanding carbon nanotube (CNT)‐V2O5 nanowire (VNW) composite paper electrodes without using binders. Coin cell type (CR2032) supercapacitors are assembled using the nanocomposite paper electrode as the anode and high surface area carbon fiber electrode (Spectracarb 2225) as the cathode. The supercapacitor with CNT‐VNW composite paper electrode exhibits a power density of 5.26 kW Kg−1 and an energy density of 46.3 Wh Kg−1. (Li)VNWs and CNT composite paper electrodes can be fabricated in similar manner and show improved overall performance with a power density of 8.32 kW Kg−1 and an energy density of 65.9 Wh Kg−1. The power and energy density values suggest that such flexible hybrid nanocomposite paper electrodes may be useful for high performance electrochemical supercapacitors.

Microbial fuel cell cathode with dendrimer encapsulated Pt nanoparticles as catalyst

In this paper, we investigated the use of polyamidoamine (PAMAM) dendrimer-encapsulated platinum nanoparticles (Pt-DENs) as a promising type of cathode catalyst for air-cathode single chamber microbial fuel cells (SCMFCs). The Pt-DENs, prepared via template synthesis method, have uniform diameter distribution with size range of 3–5 nm. The Pt-DENs then loaded on to a carbon substrate. For comparison, we also electrodeposited Pt on carbon substrate. The calculation shows that the loading amount of Pt-DENs on carbon substrate is about 0.1 mg cm −2, which is three times lower than that of the electrodeposited Pt (0.3 mg cm −2). By measuring batch experiments, the results show that Pt-DENs in air-cathode SCMFCs have a power density of 630 ± 5 mW m −2 and a current density of 5200 ± 10 mA m −2 (based on the projected anodic surface area), which is significantly better than electrodeposited Pt cathodes (power density: 275 ± 5 mW m −2 and current density: 2050 ± 10 mA m −2). Additionally, Pt-DENs-based cathodes resulted in a higher power production with 129.1% as compared to cathode with electrodeposited Pt. This finding suggests that Pt-DENs in MFC cathodes is a better catalyst and has a lower loading amount than electrodeposited Pt, and may serve as a novel and alternative catalyst to previously used noble metals in MFC applications.

Scale-up of B-doped diamond anode system for electrochemical oxidation of phenol simulated wastewater in batch mode

Scale-up of boron-doped diamond (BDD) anode system is critical to the practical application of electrochemical oxidation in bio-refractory organic wastewater treatment. In this study, the scale-up of BDD anode system was investigated on batch-mode electrochemical oxidation of phenol simulated wastewater. It was demonstrated that BDD anode system was successfully scaled up by 121 times without performance deterioration based on the COD and specific energy consumption ( E sp) models in bath mode. The COD removal rate and E sp for the scaled-up BDD anode system through enlarging the total anode area while keeping similar configuration, remained at the similar level as those before being scaled up, under the same area/volume value, current density, retention time and wastewater characteristics. The COD and E sp models used to describe the smaller BDD anode system satisfactorily predicted the performance of the scaled-up BDD anode system. Under the suitable operating conditions, the COD of phenol simulated wastewater was reduced from 540 mg l −1 to 130 mg l −1 within 3 h with an E sp of only 34.76 kWh m −3 in the scaled-up BDD anode system. These results demonstrate that BDD anode system is very promising in practical bio-refractory organic wastewater treatment.

Use of SECM to compare corrosion resistance of DIN W. Nr. 1·4460 high N and AISI 316L austenitic stainless steels in physiological solutions

The pitting corrosion resistance of DIN W. Nr. 1·4460 stainless steel (SS) with high amounts of nitrogen (0·87%) was evaluated to be used for medical implants. The SS pitting corrosion resistance was tested in a minimum essential medium at 37°C by electrochemical impedance spectroscopy and potentiodynamic polarisation curves and in a 0·1 mol L−1 NaCl solution at 25°C, by scanning electrochemical microscopy. This last technique measures the concentration of chemical species released by corrosion processes. The potential of an ultramicroelectrode was set to amperometrically detect the Fe2+ ions released at the anodic areas and also the depletion of oxygen due to the cathodic reactions in the vicinity of the cathodic areas. The AISI 316L stainless steel was also tested for comparison reasons. The results showed that the DIN W. Nr. 1·4460 with 0·87% nitrogen presents higher pitting corrosion resistance than the AISI 316L SS, being a potential candidate for biomaterial applications.

Effects of Anode and Cathode Areas on Organic Compounds Removal and Power Generation in Membraneless Microbial Fuel Cell (MFC)

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Study of Electrochemical Inhomogeneity of Zinc in Zinc/Steel Couple during Galvanize Corrosion by Wire Beam Electrode

The localized electrochemical characteristics of the anodic metal within a zinc/steel couple immersed in seawater was investigated using an Wire Beam Electrode(WBE) composed of 9 zinc wire sensors together with 112 mild steel ones. The results showed that potential and current density distributions of zinc wires were inhomogeneous; main anodic area transferred from the zinc wires adjacent to steel wires to those farther away from zinc/steel interface gradually; besides, some zinc wires behaved as secondary cathodes. This electrochemical inhomogeneity of zinc might mainly be ascribed to the dissimilar distance between zinc and mild steel wire sensors, and their surface electrochemical state as well.

Electrooxidation of Phenol on a Ti/RuO2 anode: effect of some electrolysis parameters

The influences of electrolysis time, anodic area, current density and supporting electrolyte on phenol and its byproducts degradation on a Ti/RuO2 anode were investigated. It was observed that phenol and its byproducts were rapidly broken down in the presence of chloride ions. Gas chromatography/mass spectrometry (GC/MS) data have shown that the presence of chloride ions lead to chlorophenols formation, due to reactions with Cl2 and/or OCl¯ generated during electrolysis. However, these intermediate products were also degraded later by the oxidizing agents. The standards established by the CONAMA (Brazilian National Council for the Environment) for phenols and chlorophenols in effluents were achieved after 360 min of electrolysis with a current density of 10 mA cm-2. Cyclic voltammograms obtained with the anodes before and after 436 h of electrolysis under severe salinity conditions (2 mol L-1) and current density (800 mA cm-2) showed that Ti/RuO2 did not lose its electrocatalytic properties. This fact indicates that Ti/RuO2 can be used for the treatment of effluents containing phenols in a chloride environment

Hydroxylated and aminated polyaniline nanowire networks for improving anode performance in microbial fuel cells

Hydroxylated and aminated polyaniline nanowire networks were synthesized and used as anode materials to enhance the electrical outputs of microbial fuel cells (MFCs). MFCs with these anodes generated power and current densities as high as 0.28mW cm(-2) (per geometric anode area) and 2.9mA cm(-2), respectively.

Recirculating Planar Magnetrons for High-Power High-Frequency Radiation Generation

We present designs and simulations of a new class of magnetron, the recirculating planar magnetron. This magnetron has numerous advantages as a high-power microwave generator, including larger cathode and anode area, fast start-up, and compact microwave extraction geometry. The following two geometries are demonstrated by electromagnetic particle-in-cell codes: 1) axial magnetic field with radial electric field and 2) radial magnetic field with axial electric field.