A dual-chamber microbial fuel cell with conductive film-modified anode and cathode and its application for the neutral electro-Fenton process

This study reports on the modification of the anode and the cathode in a dual-chamber microbial fuel cell (MFC) with a polypyrrole (PPy)/anthraquinone-2,6-disulfonate (AQDS) conductive film to boost its performance and the application of the MFC to drive neutral electron-Fenton reactions occurring in the cathode chamber. The MFC equipped with the conductive film-coated anode and cathode delivered the maximum power density of 823 mW cm⁻² that was one order of magnitude larger than that obtained in the MFC with the unmodified electrodes. This was resulted from the enhanced activities of microbial metabolism in the anode and oxygen reduction in the cathode owing to the decoration of both electrodes with the PPy/AQDS composite. The MFC with the modified electrodes resulted in the largest rate of H₂O₂ generation in the cathode chamber by the two-electron reduction of O₂. The increase in the concentration of H₂O₂ was beneficial for the enhancement in the amount of hydroxyl radicals produced by the reaction of H₂O₂ with Fe²⁺, thus allowing an increased oxidative ability of the electro-Fenton process towards the decolorization and mineralization of an azo dye (i.e., Orange II) at pH 7.0.     

Photoelectro-Fenton combined with photocatalytic process for degradation of an azo dye using supported TiO2 nanoparticles and carbon nanotube cathode: Neural network modeling

In this work, treatment of an azo dye solution containing C.I. Basic Red 46 (BR46) by photoelectro-Fenton (PEF) combined with photocatalytic process was studied. Carbon nanotube-polytetrafluoroethylene (CNT-PTFE) electrode was used as cathode. The investigated photocatalyst was TiO₂ nanoparticles (Degussa P25) having 80% anatase and 20% rutile, specific surface area (BET) 50 m²/g, and particle size 21 nm immobilized on glass plates. A comparison of electro-Fenton (EF), UV/TiO₂, PEF and PEF/TiO₂ processes for decolorization of BR46 solution was performed. Results showed that color removal follows the decreasing order: PEF/TiO₂ > PEF > EF > UV/TiO₂. The influence of the basic operational parameters such as initial pH of the solution, initial dye concentration, the size of anode, applied current, kind of ultraviolet (UV) light and initial Fe³⁺ concentration on the degradation efficiency of BR46 was studied. The mineralization of the dye was investigated by total organic carbon (TOC) measurements that showed 98.8% mineralization of 20 mg/l dye at 6 h using PEF/TiO₂ process. An artificial neural network (ANN) model was developed to predict the decolorization of BR46 solution. The findings indicated that artificial neural network provided reasonable predictive performance (R² = 0.986).     

Kinetic modeling of a triarylmethane dye decolorization by photoelectro-Fenton process in a recirculating system: Nonlinear regression analysis

The treatment of C.I. Acid Blue 5 solution by electrochemical process was studied under recirculation mode with a cathode containing multi walled carbon nanotubes in the presence of sodium sulfate electrolyte. Comparison of electro-Fenton and photoelectro-Fenton processes at pH 3.0 revealed that 23.04 and 98.25% of the dye was decolorized at 60 min, respectively. The kinetic of dye removal by photoelectro-Fenton process was studied with nonlinear regression analysis. A kinetic model was developed for estimation of pseudo-first order rate constant (k_app) as a function of operational parameters including initial concentration of the dye (10–50 mg/L), flow rate (5–20 L/h), pH (3–9), initial concentration of Fe³⁺ (0.05–0.2 mM) and applied current (0.05–0.45 A). The calculated results, which were obtained from kinetic model, were in consistent with the experimental data (R² = 0.9934). The calculated and experimental data were applied for prediction of the electricity consumption in decolorization processes.     

Azo and anthraquinone dye decolorization in relation to its molecular structure using soluble Trichosanthes dioica peroxidase supplemented with redox mediator

In this study we investigated the decolorizing ability of Trichosanthes dioica-derived soluble peroxidase on structurally complex azo and anthraquinone dyes in the presence of redox mediators. Our results show that riboflavin acted as a better redox mediator than antraquinone-2, 6-disulfonate (AQDS). Riboflavin served as an efficient electron transferor than AQDS in the reduction of azo dyes, by contrast with anthraquinone dyes. Although the extent of decolorization (expressed as percent dye decolorization) varied from one dye to the other, maximum decolorization was achieved for the case when suspensions containing 0.45 EU (Enzyme Units)/ml and 0.2 mM riboflavin at pH 5.0 were incubated for 2 h at 40 °C.     

Degradation of the beta-blocker propranolol by electrochemical advanced oxidation processes based on Fenton's reaction chemistry using a boron-doped diamond anode

The electro-Fenton (EF) and photoelectro-Fenton (PEF) degradation of solutions of the beta-blocker propranolol hydrochloride with 0.5 mmol dm⁻³ Fe²⁺ at pH 3.0 has been studied using a single cell with a boron-doped diamond (BDD) anode and an air diffusion cathode (ADE) for H₂O₂ electrogeneration and a combined cell containing the above BDD/ADE pair coupled in parallel to a Pt/carbon felt (CF) cell. This naphthalene derivative can be mineralized by both methods with a BDD anode. Almost overall mineralization is attained for the PEF treatments, more rapidly with the combined system due to the generation of higher amounts of hydroxyl radical from Fenton's reaction by the continuous Fe²⁺ regeneration at the CF cathode, accelerating the oxidation of organics to Fe(III)-carboxylate complexes that are more quickly photolyzed by UVA light. The homologous EF processes are less potent giving partial mineralization. The effect of current density, pH and Fe²⁺ and drug concentrations on the oxidation power of PEF process in combined cell is examined. Propranolol decay follows a pseudo first-order reaction in most cases. Aromatic intermediates such as 1-naphthol and phthalic acid and generated carboxylic acids such as maleic, formic, oxalic and oxamic are detected and quantified by high-performance liquid chromatography. The chloride ions present in the starting solution are slowly oxidized at the BDD anode. In PEF treatments, all initial N of propranolol is completely transformed into inorganic ions, with predominance of NH₄⁺ over NO₃⁻ ion.     

Electrochemical destruction of chlorophenoxy herbicides by anodic oxidation and electro-Fenton using a boron-doped diamond electrode

The degradation of herbicides 4-chlorophenoxyacetic acid (4-CPA), 4-chloro-2-methylphenoxyacetic acid (MCPA), 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) in aqueous medium of pH 3.0 has been comparatively studied by anodic oxidation and electro-Fenton using a boron-doped diamond (BDD) anode. All solutions are totally mineralized by electro-Fenton, even at low current, being the process more efficient with 1 mM Fe²⁺ as catalyst. This is due to the production of large amounts of oxidant hydroxyl radical (OH) on the BDD surface by water oxidation and from Fenton’s reaction between added Fe²⁺ and H₂O₂ electrogenerated at the O₂-diffusion cathode. The herbicide solutions are also completely depolluted by anodic oxidation. Although a quicker degradation is found at the first stages of electro-Fenton, similar times are required for achieving overall mineralization in both methods. The decay kinetics of all herbicides always follows a pseudo first-order reaction. Reversed-phase chromatography allows detecting 4-chlorophenol, 4-chloro-o-cresol, 2,4-dichlorophenol and 2,4,5-trichlorophenol as primary aromatic intermediates of 4-CPA, MCPA, 2,4-D and 2,4,5-T, respectively. Dechlorination of these products gives Cl⁻, which is slowly oxidized on BDD. Ion-exclusion chromatography reveals the presence of persistent oxalic acid in electro-Fenton by formation of Fe³⁺-oxalato complexes, which are slowly destroyed by OH adsorbed on BDD. In anodic oxidation, oxalic acid is mineralized practically at the same rate as generated.     

Electro-Fenton, UVA photoelectro-Fenton and solar photoelectro-Fenton degradation of the drug ibuprofen in acid aqueous medium using platinum and boron-doped diamond anodes

The degradation of a 41 mg dm⁻³ ibuprofen (2-(4-isobutylphenyl)propionic acid) solution of pH 3.0 has been comparatively studied by electrochemical advanced oxidation processes (EAOPs) like electro-Fenton, UVA photoelectro-Fenton and solar photoelectro-Fenton at constant current density. Experiments were performed in a one-compartment cell with a Pt or boron-doped diamond (BDD) anode and an O₂-diffusion cathode. Heterogeneous hydroxyl radical (OH) is generated at the anode surface from water oxidation, while homogeneous OH is formed from Fenton's reaction between Fe²⁺ and H₂O₂ generated at the cathode, being its production strongly enhanced from photo-Fenton reaction induced by sunlight. Higher mineralization is attained in all methods using BDD instead Pt, because the former produces greater quantity of OH enhancing the oxidation of pollutants. The mineralization rate increases under UVA and solar irradiation by the rapid photodecomposition of complexes of Fe(III) with acidic intermediates. The most potent method is solar photoelectro-Fenton with BDD giving 92% mineralization due to the formation of a small proportion of highly persistent final by-products. The effect of Fe²⁺ content, pH and current density on photoelectro-Fenton degradation has been studied. The ibuprofen decay always follows a pseudo-first-order kinetics and its destruction rate is limited by current density and UV intensity. Aromatics such as 1-(1-hydroxyethyl)-4-isobutylbenzene, 4-isobutylacetophenone, 4-isobutylphenol and 4-ethylbenzaldehyde, and carboxylic acids such as pyruvic, acetic, formic and oxalic have been identified as oxidation by-products. Oxalic acid is the ultimate by-product and the fast photodecarboxylation of its complexes with Fe(III) under UVA or solar irradiation explains the higher oxidation power of photoelectro-Fenton methods in comparison to electro-Fenton procedures.     

Mineralization of herbicide 3,6-dichloro-2-methoxybenzoic acid in aqueous medium by anodic oxidation, electro-Fenton and photoelectro-Fenton

The mineralization of acidic aqueous solutions with 230 and 115 ppm of herbicide 3,6-dichloro-2-methoxybenzoic acid (dicamba) in 0.05 M Na₂SO₄ of pH 3.0 has been studied by electro-Fenton and photoelectro-Fenton using a Pt anode and an O₂-diffusion cathode, where oxidizing hydroxyl radicals are produced from Fenton's reaction between added Fe²⁺ and H₂O₂ generated by the cathode. While electro-Fenton only yields 60-70% mineralization, photoelectro-Fenton allows a fast and complete depollution of herbicide solutions, even at low currents, by the action of UV irradiation. In both treatments, the initial chlorine is rapidly released to the medium as chloride ion. Comparative electrolyses by anodic oxidation in the absence and presence of electrogenerated H₂O₂ give very poor degradation. The dicamba decay follows a pseudo-first-order reaction, as determined by reverse-phase chromatography. Formic, maleic and oxalic acids have been detected in the electrolyzed solutions by ion-exclusion chromatography. In electro-Fenton, all formic acid is transformed into CO₂, and maleic acid is completely converted into oxalic acid, remaining stable Fe³⁺-oxalato complexes in the solution. The fast mineralization of such complexes by UV light explains the highest oxidative ability of photoelectro-Fenton.     

Electrocatalytic reduction of dioxygen at glassy carbon electrodes modified with polypyrrole/anthraquinonedisulphonate composite film in various pH solutions

Functionalized polypyrrole (PPy) film with anthraquinonedisulphonate (AQDS) incorporated as dopant was prepared by anodic polymerization of pyrrole (Py) at a glassy carbon electrode from aqueous solution. The electrochemical behavior of AQDS in PPy matrix and the electrocatalytic reduction of dioxygen on the resulting composite film were investigated in various pH solutions. The formal potential of AQDS and the reduction potential of dioxygen both exhibit pH dependence. In all pH solutions employed, the electrocatalytic reduction of dioxygen at the PPy/AQDS composite film establishes a pathway of irreversible two-electron reduction to form hydrogen peroxide. The pH 6.0 buffer solution is a more suitable medium for the reduction of dioxygen, where the PPy/AQDS composite film showed a more efficient electrocatalytic performance. It was found that AQDS is an effective mediator for the reduction of dioxygen and the reduced AQ is responsible for the enhanced catalytic activity. The catalytic current is under mixed kinetic-diffusion control. The number of electrons transferred and kinetic parameters of dioxygen reduction were determined using cyclic voltammetry, rotating disk voltammetry and Tafel polarization technique.     

Electro-Fenton degradation of antimicrobials triclosan and triclocarban

The antimicrobials triclosan (2,4,4′-trichloro-2′-hydroxydiphenyl ether) and triclocarban (N-(4-chlorophenyl)-N′-(3,4-dichlorophenyl)urea) have been degraded by four electro-Fenton systems using undivided electrolytic cells with a Pt or boron-doped diamond (BDD) anode and a carbon felt or O₂ diffusion cathode. The main oxidant is hydroxyl radical (OH) produced both on the anode surface from water oxidation and in the medium by Fenton's reaction, which takes place between electrogenerated H₂O₂ and Fe²⁺ coming from cathodic reduction of O₂ and Fe³⁺, respectively. Triclosan from saturated aqueous solutions of pH 3.0 is completely removed in all cells, decreasing its decay rate in the order: Pt/carbon felt > BDD/carbon felt > Pt/O₂ diffusion > BDD/O₂ diffusion, in agreement with their OH generation ability from Fenton's reaction. Glyoxylic, maleic and oxalic acids are identified as aliphatic intermediates. Complexes between oxalic acid and iron ions persist largely in solution, although Fe²⁺-oxalato complexes are mineralized by OH in the medium and Fe³⁺-oxalato complexes are destroyed by OH on BDD. Analogous treatments of more concentrated triclosan solutions using a 20:80 (v/v) acetonitrile/water mixture as solvent evidence the role of hydroxyl radicals along the degradation. In this hydroorganic medium hydroxylated derivatives such as 2,4-dichlorophenol, 4-chlorocatechol, chlorohydroquinone and chloro-p-benzoquinone, and carboxylic acids such as maleic, oxalic, formic and acetic acids are detected as products. Complete destruction of iron-oxalato complexes and released Cl⁻ ion involves some oxidizing species coming from parallel acetonitrile oxidation. The same electro-Fenton systems also yield the overall removal of triclocarban in acetonitrile/water mixtures, giving rise to urea, hydroquinone, chlorohydroquinone, 1-chloro-4-nitrobenzene and 1,2-dichloro-4-nitrobenzene as primary intermediates.     

Polypyrrole and La1−xSrxMnO3 (0≤ x ≤0.4) composite electrodes for electroreduction of oxygen in alkaline medium

Composite G/PPy/PPy(La_1−xSr_xMnO₃)/PPy electrodes made of the perovskite La_1−xSr_xMnO₃ embedded into a polypyrrole (PPy) layer, sandwiched between two pure PPy films, electrodeposited on a graphite support were investigated for electrocatalysis of the oxygen reduction reaction (ORR). PPy and PPy(La_1−xSr_xMnO₃) (0≤ x ≤0.4) successive layers have been obtained on polished and pretreated graphite electrodes following sequential electrodeposition technique. The electrolytes used in the electrodeposition process were Ar saturated 0.1 mol dm⁻³ pyrrole (Py) plus 0.05 mol dm⁻³ K₂SO₄ with and without containing a suspension of 8.33 g L⁻¹ oxide powder. Films were characterized by XRD, SEM, linear sweep voltammetry, cyclic voltammetry (CV) and electrochemical impedance (EI) spectroscopy. Electrochemical investigations were carried out at pH 12 in a 0.5 mol dm⁻³ K₂SO₄ plus 5 mmol dm⁻³ KOH, under both oxygenated and deoxygenated conditions. Results indicate that the porosity of the PPy matrix is considerably enhanced in presence of oxide particles. Sr substitution is found to have little influence on the electrocatalytic activity of the composite electrode towards the ORR. However, the rate of oxygen reduction decreases with decreasing pH of the electrolyte from pH 12 to pH 6. It is noteworthy that in contrast to a non-composite electrode of the same oxide in film form, the composite electrode exhibits much better electrocatalytic activity for the ORR.     

A potentiometric and voltammetric sensor based on polypyrrole film with electrochemically induced recognition sites for detection of silver ion

Conducting polypyrrole membranes were deposited on glassy carbon electrodes by electropolymerizing pyrrole in the presence of Eriochrome Blue-Black B (EBB) as the counter anion. The electrodes were then subjected to several oxidation/reduction potential steps in pure silver nitrate solution for successive accumulation/stripping of silver species. This electrochemically mediated doping/templating generated selective recognition elements in the EBB/PPy film for silver ions. The resulting sensor exhibited a considerable enhancement in the potentiometric and voltammetric response characteristics: extending the linear dynamic range and lowering the detection limit. In the potentiometric mode, the sensor showed highly reproducible response with a Nernstian slope of 58.5 ± 0.3 mV per decade of Ag⁺ activity over a linear range spanning seven orders of magnitude (1 × 10⁻⁸ to 1 × 10⁻¹ M Ag⁺), with a detection limit of ∼6 × 10⁻⁹ M. The electrodes demonstrated high selectivity over a large number of cations including alkali, alkaline earth and several transition and heavy metal ions, and could be used over a wide pH range of 1-8.5. The EBB/PPy modified electrode was also used for preconcentration and differential pulse anodic stripping voltammetric (DPASV) measurements. The DPASV peak current was dependent on the concentration of Ag⁺ over the range 3 × 10⁻¹⁰ to 1 × 10⁻⁴ M. The presence of 1000-fold excess of Cd²⁺, Cu²⁺, Cr³⁺, Co²⁺, Mn²⁺, Fe²⁺, Fe³⁺, Ni²⁺ and Pb²⁺ can be tolerated in the determination of silver ion.     

Oxidation pathways of malachite green by Fe-catalyzed electro-Fenton process

A very detailed scheme for the Fe³⁺-catalyzed electro-Fenton mineralization of malachite green as a model triarylmethane dye is presented. Bulk electrolyses of 250-mL aqueous solutions of 0.5 mM malachite green with 0.2 mM Fe³⁺ as catalyst have been carried out at room temperature and pH 3.0 under constant current in an undivided cell equipped with a graphite-felt cathode and a Pt anode to assess the performance of the electro-Fenton system. In situ electrogeneration of Fe²⁺ and H₂O₂ from quick cathodic reduction of Fe³⁺ and dissolved O₂ (from bubbled compressed air), respectively, allows the formation of the very oxidizing species hydroxyl radical (OH) in the medium from Fenton's reaction. A pseudo-first-order decay kinetics with an apparent rate constant of k_1,MG = 0.244 min⁻¹ was obtained for total destruction of malachite green by action of OH at 200 mA, requiring 22 min for total decoloration of the solution. In the same experimental conditions, overall mineralization was reached at 540 min. Up to 15 aromatic and short-chain carboxylic acid intermediates were identified along the treatment. The evolution of current efficiency was calculated from the chemical oxygen demand (COD) removal. Based on the time course of most of the by-products and the identification of inorganic ions released, some plausible mineralization pathways are proposed and thoroughly discussed. It has been found that the electro-Fenton degradation of malachite green proceeds via parallel pathways, all of them involving primary splitting of the triaryl structure initiated by attack of OH on the central carbon, thus yielding two different N-dimethylated benzophenones. Successive cleavage of the aromatic intermediates generates oxalic acid as the ultimate short-chain carboxylic acid, whereas N-demethylation of some of them produces formic acid as well. Oxalic acid and its Fe²⁺ complexes, as well as formic acid, can be slowly but totally mineralized by OH.     

Indium tin oxide coated conducting glass electrode for electrochemical destruction of textile colorants

Galvanostatic oxidation of 5.0 × 10⁻² mM textile dyes such as Eosin Y (EY) and Orange II (Or II) was carried out on an indium tin oxide (ITO) coated glass anode in the presence of 1.0 × 10⁻² mM KCl solution at pH 4.0 and 6.0. The degradation results of EY were compared with that of highly stable azo dyes (Or II). EY dye solution with a concentration of 5.0 × 10⁻² mM is totally decolorized in 30 min at an electrical charge (Q) 0.067 A h dm⁻³ while 5.0 × 10⁻² mM Or II degraded in a little less than an hour at the same electrical charge density. The decay kinetics of dyes follows a pseudo first-order reaction. The degradation of dyes is faster in acidic pH values than in basic pH values. Electrochemical degradation results show significant decrease in chemical oxygen demand (COD) values after electrodegradation of textile dyes. The key advantage of the ITO conducting glass anode is that the deposition of polymeric materials on the anode surface during electro-degradation of textile dyes is absent and therefore the electrode fouling is not observed. Hence, the ITO anodes can be employed an extended period without loss of activity.     

A bi-layered composite cathode of La0.8Sr0.2MnO3-YSZ and La0.8Sr0.2MnO3-La0.4Ce0.6O1.8 for IT-SOFCs

A bi-layered composite cathode of La_0.8Sr_0.2MnO₃ (LSM)-YSZ and LSM-La_0.4Ce_0.6O_1.8 (LDC) was fabricated for anode-supported solid oxide fuel cells with a thin YSZ electrolyte film. The cell with the bi-layered composite cathode displayed better performance than the cell with the corresponding single-layered composite cathode of LSM-LDC or LSM-YSZ. At 650 °C, the cell with the bi-layered composite cathode gave a higher maximum power density than the cells with the single-layered LSM-LDC and LSM-YSZ composite cathodes, by 52% and 175%, respectively. The impedance spectra results show that the thin LSM-YSZ interlayer not only improves the cathode/electrolyte interface but also reduces the polarization resistance of the cathode. The activation energy for oxygen reduction on the bi-layered composite cathode is much smaller than that on LSM-YSZ composite cathode, and it is suggested that the special redox property of Ce⁴⁺/Ce³⁺ in LDC facilitates the oxygen reduction process on the bi-layered composite cathode. The cell with the bi-layered composite cathode operated quite stably during a 100 h run.     

Degradation of disperse azo dyes from waters by solar photoelectro-Fenton

Solutions of the azo dyes Disperse Red 1 (DR1) and Disperse Yellow 3 (DY3), commonly used in the Chilean textile industry, in 0.1 mol dm⁻³ Na₂SO₄ and 0.5 mmol dm⁻³ Fe²⁺ of pH 3.0 were comparatively degraded by electro-Fenton (EF) and solar photoelectro-Fenton (SPEF) using a 2.5 dm³ recirculation flow plant containing a BDD/air-diffusion cell coupled with a solar photoreactor. Organics were oxidized in EF with hydroxyl radicals formed at the anode surface from water oxidation and in the bulk from Fenton's reaction between electrogenerated H₂O₂ and added Fe²⁺. The oxidizing power of SPEF was enhanced by the additional production of hydroxyl radicals from the photolysis of Fe(III) hydrated species and the photodecomposition of Fe(III) complexes with intermediates by UV light of solar irradiation. Total decolorization, complete dye removal and almost overall mineralization for both dye solutions were only achieved using the most potent SPEF process, yielding higher current efficiencies and lower energy consumptions than EF. Final carboxylic acids like pyruvic, acetic, oxalic and oxamic were detected during the SPEF treatments. NO₃⁻ ion was released as inorganic ion. The use of a solution pH of 2.0–3.0 at 50 mA cm⁻² was found preferable for SPEF. Synthetic textile dyeing solutions containing the dyes were treated under these conditions yielding lower decolorization rate, slower dye removal and smaller mineralization degree than only using 0.1 mol dm⁻³ Na₂SO₄ due to the parallel oxidation of organic dyeing components. However, lower energy consumptions were obtained by the destruction of more amounts of total organic carbon, indicating that SPEF is a useful and viable method for the remediation of textile industrial wastewaters with high contents of disperse azo dyes.     

Polypyrrole/carbon composite electrode for high-power electrochemical capacitors

Nano-thin polypyrrole (PPy) layers with thickness from ∼5 nm to several 10s nm were deposited on vapor grown carbon fibers (VGCF) by an in situ chemical polymerization. Using different concentrations of the pyrrole could control the thicknesses of deposited PPy layers. Surface morphology and thickness of the deposited PPy layers were confirmed by means of scanning electron microscopy and scanning transmission emission microscopy. Pseudo-capacitive behavior of the deposited PPy layers on VGCF investigated by means of cyclic voltammetry. Then, the PPy/VGCF composites were mixed with activated carbons (AC) at various mixing ratios. For the PPy/VGCF/AC composite electrodes, characteristics of specific capacitance and power capability were examined by half-cell tests. As results of this study, it was investigated that nano-thin PPy layer below ∼10 nm deposited on VGCF had high pseudo-capacitance and fast reversibility. Its specific capacitance per averaged weight of active material (PPy) was obtained as ∼588 F g⁻¹ at 30 mV s⁻¹ and maintained as ∼550 F g⁻¹ at 200 mV s⁻¹ of scan rate. Also, from the mixing 60 wt.% of the PPy/VGCF with 25 wt.% of AC, the PPy/VGCF/AC composite electrode exhibited higher power capability maintaining the specific capacitance per active materials of PPy and AC as ∼300 F g⁻¹ at 200 mV s⁻¹ in 6 M KOH.     

Structure and thermal properties of La0.6Sr0.4Co0.2Fe0.8O3−δ-SDC carbonate composite cathodes for intermediate- to low-temperature solid oxide fuel cells

The structure and thermal properties of La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ-SDC carbonate (LSCF-SDC carbonate) composite cathodes were investigated with respect to the calcination temperatures and the weight content of the samarium-doped ceria (SDC) carbonate electrolyte. The composite cathode powder has been prepared from La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ and SDC carbonate powders using the high-energy ball milling technique in air at room temperature. Different powder mixtures at 30 wt%, 40 wt% and 50 wt% of SDC carbonate were calcined at 750-900 °C. The findings indicated that the structure and thermal properties of the composite cathodes were responsive to the calcination temperature and the content of SDC carbonate. The absence of any new phases as confirmed via XRD analysis demonstrated the excellent compatibility between the cathode and electrolyte materials. The particle size of the composite cathode powder was ∼0.3-0.9 μm having a surface area of 4-15 m² g⁻¹. SEM investigation revealed the presence of large particles in the resultant powders resulting from the increased calcination temperature. The composite cathode containing 50 wt% SDC carbonate was found to exhibit the best thermal expansion compatibility with the electrolyte.     

A bi-layer cathode based on lanthanum based cobalt- and iron-containing perovskite and gadolinium doped ceria for thin yttria stabilized zirconia electrolyte solid oxide fuel cells

Composite cathodes based on La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF) are investigated for lower operating temperature (<750 °C) applications of a solid oxide fuel cell (SOFC). To enhance a charge transfer, a bi-layer SOFC cathode is proposed, which has a LSCF–Ce_0.9Gd_0.1O_1.95 (GDC) composite layer and a pure LSCF layer. The bi-layer cathode SOFC shows a current density of 0.65 A cm⁻² at 0.8 V and 660 °C, which is higher than a LSCF–GDC composite single-layer cathode SOFC cell of 0.35 A cm⁻². The charge transfer polarizations in the bi-layer cathode SOFC are 0.14 Ω cm² and 0.35 Ω cm² at 760 °C and 660 °C, respectively, which are lower than those in the single-layer cathode cell of 0.23 Ω cm² and 0.66 Ω cm². The impedances characterized with a fitting model show that the lowered charge transfer polarization in the bi-layer cathode is a dominant factor in reducing the total polarization of SOFC.