Anodic Resistance Research Articles

Direct methane fuel cell with La2Sn2O7–Ni–Gd0.1Ce0.9O1.95 anode and electrospun La0.6Sr0.4Co0.2Fe0.8O3−δ–Gd0.1Ce0.9O1.95 cathode

La2Sn2O7 nano-powder is synthesized by co-precipitation method. La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) and Gd0.1Ce0.9O1.95 (GDC) composite fibers are fabricated by electrospinning. Scanning electron microscopy (SEM) images show highly increased triple phase boundary (TPB) sites and pores in the electrospun cathode. The interfacial resistance of the electrospun cathode is reduced by 0.2 Ω cm2 compared to the conventional cathode at 650 °C. When dry methane fuel is fed to the anode, the reduction rate of the power density of the La2Sn2O7–Ni–GDC anode-supported cell significantly decreases compared to that of the Ni–GDC anode-supported cell at 650 °C. The anode resistance in the low frequency range (∼3 Hz) associated with methane conversion shows a remarkable difference between the La2Sn2O7–Ni–GDC and Ni–GDC anode. Temperature-programmed reduction (TPR) analysis reveals the La2Sn2O7 catalyst is effective for the methane oxidation reaction at 650 °C. The Fuel cell in this study manifests a maximum power density of 1.02 W cm−2 and 0.94 W cm−2 at 650 °C in hydrogen and dry methane atmosphere, respectively. Also, no carbon deposition existed on the La2Sn2O7–Ni–GDC anode after operating.

Anodic Behavior and Corrosion Resistance of the Pb-MnO2 Composite Anodes for Metal Electrowinning

In this study, integrity and corrosion properties of the Pb-MnO2 composite anodes fabricated through single-action powder pressing were investigated. The effects of the MnO2 content on the properties of the composite anodes were studied and compared with those of the Pb and Pb-Sn-Ca anodes. Galvanostatic experiments (50 mA/cm2) were performed in stagnant sulphuric acid solution at 37°C for the durations of 24 and 72 hours. The results indicated that the Pb-MnO2 anodes operated at lower potentials than the Pb-Sn-Ca anode. The electrocatalytic activity of the composite anodes was improved as their MnO2 content increased, however, high MnO2 contents resulted in electrochemically unstable anodes. The composite anodes showed a lower degradation rate and better corrosion resistance compared to the Pb-Sn-Ca anode. Surface morphology and structure of the anodic layer on the anodes were examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Barrier properties of the anodic layer on the electrodes were investigated through cyclic voltammetric measurements. Results revealed that formation of the surface anodic layer was enhanced on the Pb-MnO2 anodes. The anodic layers formed on the composite anodes in 72-hour polarization were more compact than that of the Pb-Sn-Ca anode and provided higher levels of protection.

Composite-coated aluminum bipolar plates for PEM fuel cells

Aluminum-based bipolar plates for proton exchange membrane (PEM) fuel cells offer high strength and durability while weighing up to 65% less than stainless steel. To protect the aluminum from electrochemical corrosion while maintaining electrical conductivity, coatings that are a composite of a fluoropolymer and one or more conductive inorganic fillers were investigated. Titanium carbide (TiC) and graphite were found to be the best candidates for conductive fillers among six powders that were tested for acid and electrochemical stability. Composite coatings of graphite, TiC, and ethylene-tetrafluoroethylene (ETFE) were applied to the aluminum or ceramic substrates by wet spraying followed by heat treatment, and then tested for in-plane sheet resistance, through-plane area specific resistance (ASR), electrochemical corrosion resistance, flexural strength, and flexibility. The composite-coated aluminum plates meet the U.S. DOE targets for bipolar plates for in-plane conductivity, flexural strength, and cathodic corrosion resistance. The targets for through-plane ASR and anodic corrosion resistance were not met due to the spraying process producing an undesirable layered microstructure and also a microstructure with connected porosity and pinholes.

Electrochemical impedance spectroscopy as a diagnostic tool for the evaluation of flow field geometry in polymer electrolyte membrane fuel cells

In the present study, two different designs of flow field have been evaluated by electrochemical impedance spectroscopy for polymer electrolyte membrane fuel cells. Ex-situ experiments were conducted in serpentine and interdigitated flow field geometry. We have investigated the serpentine type flow field designs with varying rib and channel width geometry and studied their influence on the PEMFC performance. The anodic and cathodic resistances were also evaluated using symmetrical mode of operation. The three different types of multichannel serpentine geometry with 2, 1 and 0.7 mm rib and channel widths were used for evaluation and found that the mass transfer resistance was decreasing with rib& channel width thickness. The mass transfer resistance decreased by one order from 0.197 Ω for 2 mm channel width to 0.016 Ω for 0.7 mm channel width. The maximum power density obtained for PEMFC operating on H2/Air at 50 °C, with 0.7, 1&2 mm rib and channel width was found to be 365, 291 and 202 mW/cm2 respectively. This study emphasized the effect of rib and channel width geometry of flow fields by symmetrical mode of fuel cell operation using electrochemical impedance spectroscopy to obtain the anodic and cathodic mass transfer resistance individually.

Direct electro-oxidation of acetic acid in a solid oxide fuel cell

This work aims to investigate the efficiency of Cu–CeO2 as anodic composites in direct CH3COOH fed SOFC reactors for power generation. When the cell operated as an electrochemical membrane reactor, the effect of temperature, PCH3COOH and anodic overpotentials on the catalytic activity and selectivity of Cu/CeO2 for CH3COOH decomposition and electro-oxidation at both open and closed circuit operation was explored. In addition, in situ DRIFT spectroscopy was employed in order to correlate the Cu–CeO2 performance with its surface chemistry. In the fuel cell mode, the electrochemical performance of Cu–CeO2 was investigated by voltage–current density–power density and AC impedance measurements. The results reveal that at open circuit conditions, CH3COOH and its derived carbonaceous and oxygenate active intermediates are both thermally and catalytically decomposed to final products. At anodic polarization conditions, Cu–CeO2 exhibited high catalytic activity towards the electro-oxidation of all combustible species, while carbon deposition was noticeably limited. At fuel cell operation, ohmic losses were the prevailing source of polarization, mainly attributed to the anodic interfacial resistance, which is significantly influenced by temperature and fuel type. The deconvolution of the impedance spectra fitted into the Randles circuit, showed that at CH3COOH containing reacting mixtures, the electrode performance was mainly determined by the corresponding charge transfer processes of the existing combustible species. On the other hand, when H2/He mixtures were fed in the cell, diffusion resistance altered the performance of Cu–CeO2 electrodes.

Transparent indium oxide films doped with high Lewis acid strength Ge dopant for phosphorescent organic light-emitting diodes

We report on Ge-doped In2O3(IGO) films prepared by co-sputtering GeO2 and In2O3 targets for anode of phosphorescent organic light-emitting diodes (POLEDs). Under optimized annealing conditions, the IGO film exhibited a low sheet resistance of 14.0 Ω/square, a high optical transmittance of 86.9% and a work function of 5.2 eV, comparable to conventional Sn-doped In2O3 (ITO) films. Due to the higher Lewis acid strength of the Ge4+ ion (3.06) than that of Sn3+(1.62), the IGO film showed higher transparency in the near infrared and higher carrier mobility of 39.16 cm2 V−1 s−1 than the ITO films. In addition, the strongly preferred (2 2 2) orientation of the IGO grains, caused by Zone II grain growth during rapid thermal annealing, increased the carrier mobility and improved the surface morphology of the IGO film. POLEDs fabricated on IGO anodes showed identical current density–voltage–luminance curves and efficiencies to POLEDs with ITO electrodes due to the low sheet resistance and high transmittance of the IGO anode.

3D Non-destructive morphological analysis of a solid oxide fuel cell anode using full-field X-ray nano-tomography

An accurate 3D morphological analysis is critically needed to study the process–structure-property relationship in many application fields such as battery electrodes, fuel cells and porous materials for sensing and actuating. Here we present the application of a newly developed full field X-ray nano-scale transmission microscopy (TXM) imaging for a non-destructive, comprehensive 3D morphology analysis of a porous Ni–YSZ solid oxide fuel cell anode. A unique combination of improved 3D resolution and large analyzed volume (∼3600 μm3) yields structural data with excellent statistical accuracy. 3D morphological parameters quantified include phase volume fractions, surface and interfacial area densities, phase size distribution, directional connectivity, tortuosity, and electrochemically active triple phase boundary density. A prediction of electrochemical anode polarization resistance based on this microstructural data yielded good agreement with a measured anode resistance via electrochemical impedance spectroscopy. The Mclachlan model is used to estimate the anode electrical conductivity.

Anodic biofilm in single-chamber microbial fuel cells cultivated under different temperatures

The microorganisms in anodic biofilms of a microbial fuel cell (MFC) oxidize substrates to generate electrons, protons, and metabolic products. This study started up two single-chamber MFCs at different temperatures (25 °C for MFC A and 15 °C for MFC B); after successful startup, the cell temperatures were swapped. The MFC A had peak voltage at 540 mV at 25 °C, which was decreased rapidly as fed substrate was consumed. At 15 °C, the MFC A yielded a nearly constant voltage of 500 mV over complete feed cycle. Conversely, the MFC B produced higher maximum power than MFC A, and can deliver nearly constant voltage over the entire feed cycle at either 15 or 25 °C. Electrochemical analysis revealed that the MFC B had lower internal resistance than MFC A, with the former having much lower anodic resistance than the latter. Microbial analysis showed that the MFC started up at low temperatures had anodic biofilm enriched with psychrophilic bacteria Simplicispira psychrophila LMG 5408(T)[AF078755] and Geobacter psychrophilus P35(T)[AY653549]. This study suggests the strategy to promote the development of anodic biofilms at low temperatures that are capable of yielding electricity at constant voltage.

Characterization of the internal resistance of a plant microbial fuel cell

The objective of this research was to clarify the internal resistance of the PMFC. To characterize internal resistances of the PMFC current interrupt and polarization were used, and partial resistances were calculated. The internal resistance consisted mainly of anode resistance and membrane resistance which both decreased during current interrupt. The anode resistance was the result of mass transfer resistance in the electrochemically active biofilm. The membrane resistance was the result of accumulation of cations in the cathode. The polarization showed a distinct hysteresis which was explained by the increase of the internal resistance during polarization. The increase of this resistance makes it difficult to interpret the maximum power output of the PMFC.

Acetic acid internal reforming in a solid oxide fuel cell-reactor using Cu–CeO2 anodic composites

Abstract This work targets to explore the performance of Cu–CeO 2 anodes for the production of hydrogen and power generation during the internal steam reforming of CH 3 COOH in SOFC reactors. When the cell operated as an electrochemical membrane reactor, the effect of temperature, reactants' partial pressures and imposed overpotentials on the catalytic activity and selectivity of Cu/CeO 2 electrodes, at both open and closed circuit operations, were investigated. The results show that at open circuit conditions, CH 3 COOH is efficiently reformed by H 2 O to syngas, where the observed products' distribution is influenced by both the associated CH 3 COOH thermal/catalytic decomposition reactions and by the reverse water gas shift reaction. In all cases examined, neither acetone nor carbon is observed at the effluents, with the latter being attributed to the gasification of carbonaceous deposits by H 2 O to CO and H 2 . At anodic polarization conditions, Cu–CeO 2 exhibits high catalytic activity toward the electro-oxidation of all combustible species. Kinetic experiments show that the reaction mechanism involves the dissociative adsorption and decomposition of both reactants on the catalyst surface, where the subsequent interaction of the resulted fragments leads to the observed final products. In the fuel cell mode, the electrochemical performance of Cu–CeO 2 was investigated by voltage–current density–power density and AC impedance measurements. Ohmic losses are the prevailing source of polarization, mainly attributed to the anodic interfacial resistance, which is significantly influenced by cell temperature and reactants composition. The electrode performance is mainly limited by the diffusion of the charged or neutral species to triple phase boundary while in the case of dry feeding mixtures, the charge transfer processes determine the overall efficiency.

Hydrogen-fed PEMFC: Overvoltage analysis during an activation procedure

The present study aims at obtaining a better understanding on the changes that the membrane electrode assembly (MEA) of a H2-fed fuel cell experiences along an activation procedure. An activation protocol was set-up considering six loading cycles performed at 25°C. After each loading cycle, the electrochemical characterization was performed using polarization curves, Linear Sweep Voltammetry (LSV), Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). Polarization curves showed an effective increase of the MEA performance along the activation procedure, with the maximum power density increasing from 116.1mWcm−2 to 229.9mWcm−2 and the overall efficiency increasing from 9.3% to 19.7%. Simultaneously, it was observed a decrease on the Tafel slope and an increase on the exchange current density, indicating improved catalyst characteristics. From the LSV experiments it was concluded that hydrogen crossover at open circuit increases along the activation procedure, however the open circuit voltage (OCV) also increases, mainly due to an overvoltage decrease caused by mixed potential. CV experiments showed that the available catalyst area also increases. From the impedance experiments it was observed that the proton exchange membrane (PEM) and the anode and cathode charge transfer resistances decrease along the activation cycles. The opposite trend was verified for the anode and cathode double layer capacitances.

Electrochemical performance of a Pb/Pb-MnO2 composite anode in sulfuric acid solution containing Mn2+

The influence of Mn2+ on oxygen evolution kinetics and corrosion behaviour of Pb/Pb-MnO2 composite anode in sulfuric acid electrolyte was investigated using SEM, XRD, and several electrochemical methods. The results indicate that a high concentration of Mn2+ (e.g. 3.0gL−1) in the electrolyte resulted in the formation of a MnO2 layer on the surface of the anode. This layer decreased the oxygen evolution activity of the anode, but at the same time made the underlying PbO2 layer more compact and flat, effectively improving the anodic corrosion resistance. When the Mn2+ concentration was low (e.g. 0.1gL−1), no MnO2 layer was formed but the structure of the PbO2 anodic layer was modified. As a result, the oxygen evolution activity and corrosion resistance were both significantly improved. In addition, Mn2+ in the electrolyte did not change the kinetic mechanism of oxygen evolution reaction. The reaction was exclusively controlled by the formation and adsorption of first intermediate, and the adsorption resistance played a dominant part in the whole reaction resistance.

Enhanced electrochemical performance of BaZr 0.1Ce 0.7Y 0.1Yb 0.1O 3− δ electrodes for hydrogen and methane oxidation in solid oxide fuel cells by Pd or Cu 0.5Pd 0.5 impregnation

The anode material BaZr 0.1Ce 0.7Y 0.1Yb 0.1O 3− δ (BZCYYb) for solid oxide fuel cells (SOFCs) is prepared by solid state reaction method and its chemical compatibility with Y 2O 3 stabilized ZrO 2 (YSZ) is evaluated. The electrochemical performance of the pure and Pd- and Cu 0.5Pd 0.5-impreganated BZCYYb electrodes is characterized in the temperature range between 650 and 750 °C by AC impedance spectroscopy in H 2 and/or CH 4 atmospheres, respectively, under the condition of open circuit. It is confirmed that the BZCYYb is chemically compatible with the YSZ at temperatures below 1000 °C. The polarization resistance of the BZCYYb anode in H 2 is decreased from 2.08 to 0.51 Ω cm 2 as the measuring temperature increases from 650 to 750 °C with an activation energy of 117 kJ mol −1. With Pd- or Cu 0.5Pd 0.5-impregnation, the polarization resistance of the BZCYYb electrode in H 2 is reduced significantly to approximately 0.40 Ω cm 2 at 650 °C and 0.12 Ω cm 2 at 750 °C. With dry CH 4 as the fuel, the polarization resistance of the Pd- and Cu 0.5Pd 0.5-impregnated BZCYYb anodes is obviously increased below 1.00 Ω cm 2 at 650 °C and 0.22 Ω cm 2 at 750 °C. Both Pd and Cu 0.5Pd 0.5 impregnations are equivalently effective in enhancing the electrochemical performance of the BZCYYb anode.

Thermogalvanic corrosion of Alloy 31 in different heavy brine LiBr solutions

Thermogalvanic corrosion generated between two electrodes of Alloy 31, a highly-alloyed austenitic stainless steel (UNS N08031), has been investigated imposing different temperature gradients in three deaerated LiBr solutions, under open circuit conditions by using a zero-resistance ammeter (ZRA). Besides EIS spectra were acquired in order to explain the obtained results. On the whole, cold Alloy 31 electrodes were anodic to hot Alloy 31 electrodes, since an increase in temperature favoured the cathodic behaviour of the hot electrode. Thermogalvanic corrosion of Alloy 31 in the LiBr solutions studied was not severe, although it negatively affects the corrosion resistance of the cold anode. The protective properties of the passive film formed on the anode surface were found to improve with thermogalvanic coupling time.

Oxygen evolution and corrosion behaviors of co-deposited Pb/Pb-MnO 2 composite anode for electrowinning of nonferrous metals

The oxygen evolution and corrosion behaviors of Pb/Pb-MnO 2 composite anode in H 2SO 4 solution were investigated comparing with Pb and industrial Pb-Ag (1.0%) anodes. Its electrocatalytic activity towards oxygen evolution reaction (OER) and corrosion resistance were evaluated using galvanostatic polarization and ionic equilibrium method. The microcosmic morphology of the anodic layer during the polarization was observed using Scanning Electron Microscope (SEM). The results indicate that this kind of composite anode displays particular anodic behaviors during the galvanostatic polarization due to the changes of surface state: A “potential valley” with the minimal potential of about 300 mV lower than that of Pb anode can be observed at the very beginning of the polarization; then the anodic potential gradually decrease. The stable potential after 72 h is 100–150 mV lower than that of Pb anode and comparable to industrial Pb-Ag (1.0%) anode. Furthermore, the corrosion resistance of the composite anode largely depends on the MnO 2 content in deposit. The dissolution of Pb is very little at the early stage, then, after standing a period of heavy intergranular corrosion, a stationary PbO 2-MnO 2 composite layer will be formed on the anode surface, which is predicted to present satisfactory corrosion resistance in the long-time electrolysis.

Improvement of interface interaction and conductive anodic filament resistance through amphiphilic oligomeric silane

AbstractIn this article, an amphiphilic oligomeric silane (OS) was synthesized as a coupling agent to improve the interface bonding between resin matrix and glass fiber. The effect of the OS coupling agent on the interface of glass fiber/epoxy resin was studied by contact angle measurement, gravimetric measurements of water sorption, scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDX), and conductive anodic filament (CAF) resistance test. With the addition of the OS to the composites, the contact angle between epoxy resin and glass fiber decrease notably. Normalized water sorption by gravimetric measurements showed that the interfacial debonding time of composites with the OS can be prolonged significantly. CAF tests were also consistent with the water sorption results, which suggest that the gravimetric measurement of water sorption is a cost‐effective method to assess the CAF resistance of materials. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.

Redox of Ni/YSZ anodes and oscillatory behavior in single-chamber SOFC under methane oxidation conditions

A single-chamber solid oxide fuel cell made of Ni/YSZ anodes, YSZ electrolytes and SDC-impregnated LSM cathodes was tested in methane–oxygen mixture at furnace temperature equal to 700 °C. Two Ag wires were arranged on the anode surface to in situ measure the changes of the local anode resistance ( R s) during testing. Oscillations of the R s, the cell voltage and the actual temperature of the cell were observed and attributed to Ni/NiO redox cycles. Steady-state tests of the cell showed the corresponding oscillation patterns mainly depended on methane-to-oxygen ratio ( M = 1, 2). Higher current density ( J) to a certain extent could suppress NiO reduction and promote Ni oxidation. Scanning electron micrographs confirmed that Ni/NiO redox cycles had occurred mainly near the anode surface. The obtained results imply that gradual reoxidation of the Ni-anodes accompanying the various oscillation behaviors plays an important role in the degradation of the SC-SOFCs, especially under oxidation conditions.

Corrosion of dissimilar alloys: Electrochemical noise

A new approach for interpreting the electrochemical noise generated by freely corroding electrodes is presented. For a single electrode, with well-defined anodic and cathodic regions, it is proposed that the instantaneous values of the corrosion current and open circuit potential are functions of the time-invariant potential difference between the anodic and cathodic reactions and the time-dependent impedances associated with the anodic and cathodic reactions. The fluctuations in the values of anodic and cathodic impedances are determined by the interaction between the aggressive environment and the oxide, hydroxide or adsorbed surface layer covering the anodic and cathodic regions; the instantaneous values of impedances modulate the corrosion current. The mathematical implications of these assumptions are discussed and the results are compared with the traditional approach, based on time-dependent current sources acting on constant impedances. Subsequently, the findings for a single electrode are transferred to two dissimilar electrodes and an experimental technique that enables the estimation of the time evolution of anodic and cathodic resistances for each of the dissimilar electrodes is presented.

Performance of a scaled-up Microbial Fuel Cell with iron reduction as the cathode reaction

Scale-up studies of Microbial Fuel Cells are required before practical application comes into sight. We studied an MFC with a surface area of 0.5 m 2 and a volume of 5 L. Ferric iron (Fe 3+) was used as the electron acceptor to improve cathode performance. MFC performance increased in time as a combined result of microbial growth at the bio-anode, increase in iron concentration from 1 g L −1 to 6 g L −1, and increased activity of the iron oxidizers to regenerate ferric iron. Finally, a power density of 2.0 W m −2 (200 W m −3) was obtained. Analysis of internal resistances showed that anode resistance decreased from 109 to 7 mΩ m 2, while cathode resistance decreased from 939 to 85 mΩ m 2. The cathode was the main limiting factor, contributing to 58% of the total internal resistance. Maximum energy efficiency of the MFC was 41%.

Reoxidation behavior of Ni–Fe bimetallic anode substrate in solid oxide fuel cells using a thin LaGaO3 based film electrolyte

The reoxidation behavior of a Ni–Fe metal anode supported cell using a thin LaGaO3 electrolyte film was investigated as a function of the reoxidation temperature. After oxidation and reduction treatments for 2h, the voltage did not return to the initial voltage at higher temperatures (773–973K); however, after reoxidation at 673K, the cell exhibited almost the same OCV as the as-prepared cell. During reoxidation with air at the higher temperatures, the Ni–Fe metal substrate exhibited two different expansion behaviors by the different oxidation rates of Ni and Fe. On the other hand, the volumetric change of the oxidized substrate at 673K was negligible. SEM-EDX results exhibited the reoxidation of Ni–Fe occurred only at the bottom part of the substrate and at the interface between the electrolyte and the substrate. In spite of temperatures as low as 673K, the cell generated a power of 160mWcm−2, which hardly decreased after the redox cycle. The increasing anodic internal resistance accompanied with unreduced Fe.