Aluminum Cathode Research Articles

Distributed PEFC Performance during Cationic Contamination

In our previous studies (1-3), severe performance degradation of PEFCs was observed due to cationic impurities. In this study, we investigate how cations affect the spatial performance distribution in a PEFC using a segmented cell.The segmented cell hardware consists of an aluminum anode flow field, a segmented aluminum cathode flow field, two aluminum end plates and one cupper current collector. All the aluminum parts were gold plated. Cathode flow field was divided into eight segments. Eight pieces of equal size aluminum current collectors were placed inside a PTFE block and straight flow channels were machined through both the PTFE and the aluminum segments (Figure 1). Total active area of the cell was 5 cm2. 2.85 mM CaSO4solution was introduced in the air stream through a nebulizer (1-3) at a rate of 110 uL/min, corresponding to 21.2 ppm based on dry air flow rate.Figure 2 shows the voltage and current density distribution profile in each segment. The cell was operated at a constant total current of 1 A. During the baseline test of 24 hours, pure air was injected through cathode. The current in each segment remained constant through this period. Following the baseline test, the contaminant was injected in the air stream. The segments closest to the gas inlet were first affected by the contaminant. The current density in the segments closest to the gas inlet decreased while the segments closest to the outlet increased. Since it was a constant current test, when the current in the segments closest to the gas inlet decrease, other segments picked up that current to maintain total current constant.During the baseline test, voltage remained constant in all segments. After contaminant injection, the cell voltage started to decrease and after 50 hours, voltages in each segments fluctuated. The voltage fluctuation was found to be mainly due to mass transport loss. The contaminant solution evaporated and deposited on the flow field and the GDL surface (Figure 3), and entered into the GDL which caused the mass transport losses. Moreover, the aluminum flow fields corroded and corrosion byproducts also deposited on the flow field and GDL surface. Throughout the test, there was no significant variation in voltage between segments. Acknowledgements The authors gratefully acknowledge financial support from NSF (CBET-0748063), DOE-EERE through University of Hawaii-Hawaii Natural Energy Institute (DE-EE0000467).

Large work function shift of organic semiconductors inducing enhanced interfacial electron transfer in organic optoelectronics enabled by porphyrin aggregated nanostructures

We report on large work function shifts induced by the coverage of several organic semiconducting (OSC) films commonly used in organic light emitting diodes (OLEDs) and organic photovoltaics (OPVs) with a porphyrin aggregated layer. The insertion between the organic film and the aluminum cathode of an aggregated layer based on the meso-tetrakis(1-methylpyridinium-4-yl) porphyrin chloride (porphyrin 1), with its molecules adopting a face-to-face orientation parallel to the organic substrate, results in a significant shift of the OSC work function towards lower values due to the formation of a large interfacial dipole and induces large enhancement of either the OLED or OPV device efficiency. OLEDs based on poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-2,1′,3-thiadiazole)] (F8BT) and incorporating the porphyrin 1 at the cathode interface exhibited current efficiency values up to 13.8 cd/A, an almost three-fold improvement over the efficiency of 4.5 cd/A of the reference device. Accordingly, OPVs based on poly(3-hexylthiophene) (P3HT), [6,6]-phenyl-C61 butyric acid methyl ester (PC61BM) and porphyrin 1 increased their external quantum efficiencies to 4.4% relative to 2.7% for the reference device without the porphyrin layer. The incorporation of a layer based on the zinc meso-tetrakis (1-methylpyridinium-4-yl)porphyrin chloride (porphyrin 2), with its molecules adopting an edge-to-edge orientation, also introduced improvements, albeit more modest in all cases, highlighting the impact of molecular orientation.

A portable air-aluminum power source with an alkaline electrolytic solution

The results from development of a portable air-aluminum chemical power source (AA CPS) with an alkaline electrolytic solution without any additional service circuits are presented. The feasibility of making air cathodes on the basis of a metal-carbon composite produced by the plasma method has been shown. Special features of the operational conditions of a portable AA CPS have been investigated. It has been found that the aluminum cathode passivation when aluminum hydroxide precipitates from a solution significantly restricts the specific capacity of such power sources. It was shown that it is possible to overcome the anode passivation and to considerably increase the specific capacity of an AA CPS with an alkaline electrolytic solution by means of modifying an anode alloy.

Flexible PTB7:PC71BM bulk heterojunction solar cells with a LiF buffer layer

Bulk heterojunction solar cells were fabricated using poly[4,8-bis[(2-ethylhexyl)oxy]benzo [1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]-thiophenediyl] (PTB7) and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) after a layer of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) was deposited on a flexible indium tin oxide (ITO)-coated polyethylene terephthalate substrate. The fabricated structures were Al/LiF/PTB7:PC71BM/PEDOT:PSS/ITO with or without a lithium fluoride (LiF) buffer layer, and the effect of the LiF buffer layer on the performance of the solar cells was investigated. The LiF layer significantly increased the open-circuit voltages and fill factors of the solar cells, presumably because of the work function shift of the aluminum cathode. As a result, the conversion efficiency increased from 2.31 to 4.02% owing to the presence of the LiF layer. From the results of a stability test, it was concluded that the inserted LiF layer acted as a shielding and scavenging protector, which prevented the intrusion of some chemical species into the active layer, thereby improving the lifetime of the unpakcaged devices.

Organic Solar Cells Based on PTB7:PC71BM with Cs2CO3 as a Cathode Buffer Layer

Bulk heterojunction solar cells were fabricated using poly[[4,8-bis[(2-ethylhexyl)oxy]benzo [1,2-b:4,5-b']dithiophene-2,6-diyl] [3-fluoro-2- [(2-ethylhexyl)carbonyl]thieno[3,4-b]-thiophenediyl] (PTB7) and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) after a layer of poly(3,4- ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) was deposited on an indium tin oxide (ITO)-coated glass substrate. The fabricated structures were glass/ITO/PEDOT:PSS/PTB7:PC71BM/Cs2CO3/Al with or without the cesium carbonate (Cs2CO3) buffer layer, and the effect of the buffer layer on the performance of the solar cells was investigated. The Cs2CO3 layer with a thickness of 0.8 nm significantly increased the short circuit current density, open-circuit voltages and fill factors of the solar cells, presumably because of the better contact between the active layer and the cathode and the work function shift of the aluminum cathode. As a result, the power conversion efficiency increased from 1.09 to 2.12%. However, when thickness of the Cs2CO3 exceeded 2 nm, significant degradation was observed. From the results of a stability test, it was suggested that the inserted Cs2CO3 layer had a minimal influence on the lifetime of the unpakcaged devices.

RESEARCH OF PROPERTIES OF SPRAYED COATINGS ON THE ALUMINIUM ALLOYS / ALIUMINIO LYDINIŲ PLAZMINIO PURŠKIMO TYRIMAS

In article the cathodic cleaning processes of aluminum alloyAW 5754 and cleaned substrate surface coating by plasmawith Ni-Cr-Fe-Si powder were researched. Aluminium substrateroughness after cathodic treatment at different cathodic treatmentparameters was established during the experiments. During theinvestigation a comparison of the calculated medium power1.6 to 9 kW plasma torch voltage-current characteristics withthe experimental results was made. The optimized parametersof aluminium cathode substrate cleaning process were selected;porosity and morphology of plasma sprayed nickel-based coatingwere determined. Santrauka Straipsnyje nagrinėjami aliuminio lydinio AW 5754 katodinio valymo procesai ir nuvalyto substrato paviršiaus dengimas plazminiu būdu Ni-Cr-Si-Fe danga. Eksperimentinių bandymų metu nustatytas aliuminio substrato šiurkštumas po katodinio valymo, esant skirtingiems katodinio valymo parametrams. Tyrimo metu buvo palygintos apskaičiuotos vidutinės galios 1,6–9 kW plazmotrono voltamperinės charakteristikos su eksperimentiniais rezultatais. Parinkti aliuminio substrato optimalūs katodinio valymo proceso parametrai ir nustatytas plazminiu būdu užpurkštos nikelio pagrindo dangos porėtumas ir morfologija.

A fluorene-based material containing triple azacrown ether groups: synthesis, characterization and application in chemosensors and electroluminescent devices

We design a novel multifunctional fluorene-based material containing triple azacrown ether (FTC) not only for application in aqueous solution as a chemosensor towards Fe(3+) but also to enhance the electroluminescence of PLEDs using an environmentally stable aluminum cathode. The photo-physical and sensing properties were investigated by absorption and photoluminescence (PL) spectroscopy. The FTC exhibited specific selectivity and high sensitivity toward Fe(3+), with the Stern-Volmer coefficients (Ksv) being 1.59 × 10(5) M(-1) in a solvent mixture of tetrahydrofuran and water (THF-H2O = 9/1, v/v). The FTC maintained high selectivity toward Fe(3+) in the presence of ten interfering metal cations. The HOMO and LUMO levels were estimated to be -5.88 eV and -2.88 eV, respectively. The FTC significantly enhances the emission performance of PLEDs [ITO/PEDOT:PSS/MEH-PPV/EIL/Al] when used as an electron injection layer (EIL), especially in the presence of metal carbonates. Particularly, the device using K2CO3 doped FTC as the electron-injection layer (EIL) exhibited significantly enhanced performance compared to the one without EIL. The performance was significantly enhanced to 11 630 cd m(-2) and 1.47 cd A(-1), respectively, from 230 cd m(-2) and 0.03 cd A(-1) of the non-FTC device. Current results indicate that multifunctional fluorene-based material FTC is a potential candidate for selective detection of Fe(3+) and as an effective electron injection layer to enhance the performance of MEH-PPV.

A MEHPPV/VOPcPhO composite based diode as a photodetector

We demonstrate a solution-processed visible wavelength photodetector using an organic semiconductor blend of poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylene vinylene] (MEHPPV) and vanadyl 2,9,16,23-tetraphenoxy-29H,31H-phthalocyanine (VOPcPhO) to function as the donor (D) and the acceptor (A) materials, respectively. The photodetector was fabricated in the vertical geometry of ITO/PEDOT:PSS/MEHPPV:VOPcPhO/Al and the effects of varying levels of illumination on photodetector's electrical parameters were studied. Aqueous solution of PEDOT:PSS [poly(3,4-ethylendioxythiophene):poly(styrensulfonate)] and solution of D/A materials in chloroform were sequentially spun coated on the cleaned ITO coated glass substrate. Aluminum (Al) cathodes were later thermally deposited on top of the active layer through a shadow mask with circular openings of 2mm2. The photoluminescence (PL) spectra of D/A blends have been studied to optimize the volumetric ratio of the blend. The UV–vis spectrum shows that organic blend exhibits a broad absorption over almost the whole visible range. By virtue of its enhanced visible light absorbing capability, the organic blend has been utilized to fabricate the photodetector. The sensor showed an efficient photo-current response as a function of varied illumination levels. Further the detector revealed prompt reversible electrical changes versus variation in illumination levels. Since this proposed photodetector can harvest incident photons over almost the whole visible range and is inexpensive to manufacture, therefore, it has a great potential for practical applications.

Revealing the Active Layer Morphology within Complete Solar Cell Devices via Spectroscopic Ellipsometry

We used spectroscopic ellipsometry to simultaneously reveal the distribution of the fullerene component, as well as the formation of higher ordered polymer domains, within the active layer of organic solar cells. In contrast to other measurement techniques, both informations can be obtained nondestructively on postcathode annealed encapsulated solar cell devices. We observe a preferential attraction of [6,6]-phenyl-C61-butyric acid methyl ester toward the aluminum cathode, which is consistent with simple energetic considerations based on the estimated free surface energy of the cathode. Because of the increased nucleation rate in regions with high fullerene concentration and at the interfaces, we observed a reduction of the average domain size of ordered poly(3-hexylthiophene) regions in these areas, which manifests itself in a reduction of the volume fraction of highly ordered polymer domains.

Intérêt et précision d’un logiciel de navigation dans la mise en place de prothèse de hanche : à partir d’une série prospective de 75 cas

In this article, we report a highly efficient bilayer OLED with a maximum luminance up to 62 000 cd/m2 and a threshold voltage of 3.8 V. The device structure is indium-tin-oxide (ITO)/N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-diphenyl-4,4′-diamine (TPD)/tris-(8-hydroxyquinoline) aluminum (Alq3)/LiF/Al. Ion beam assisted deposition (IBAD) process is used to deposit the aluminum cathode on the LiF layer. The IBAD process improves the OLED performance both by increasing the maximum luminance by a factor of 3 and by reducing the threshold voltage for light-emission. The IBAD process also enhances the microstructure and morphology of the Al layer and leads to denser and more homogeneous layers. The resulting highly-packed microstructure acts as a barrier to moisture and oxygen and inhibits their penetration into the Alq3 layer, leading to the OLED lifetime and stability increasing. In order to optimize the IBAD process parameters, prior to the OLED deposition, we have characterized aluminum films deposited on glass substrates by using atomic force microscopy and X-ray diffraction.

Kerr electro-optic field mapping study of the effect of charge injection on the impulse breakdown strength of transformer oil

The smart use of charge injection to improve breakdown strength in transformer oil is demonstrated in this paper. Hypothetically, bipolar homo-charge injection with reduced electric field at both electrodes may allow higher voltage operation without insulation failure, since electrical breakdown usually initiates at the electrode-dielectric interfaces. To find experimental evidence, the applicability and limitation of the hypothesis is first analyzed. Impulse breakdown tests and Kerr electro-optic field mapping measurements are then conducted with different combinations of parallel-plate aluminum and brass electrodes stressed by millisecond duration impulse. It is found that the breakdown voltage of brass anode and aluminum cathode is ∼50% higher than that of aluminum anode and brass cathode. This can be explained by charge injection patterns from Kerr measurements under a lower voltage, where aluminum and brass electrodes inject negative and positive charges, respectively. This work provides a feasible approach to investigating the effect of electrode material on breakdown strength.

The effects of additives on the electrowinning of zinc from sulphate solutions with high fluoride concentration

Effects of additives on zinc electrowinning from zinc sulphate aqueous solution with a higher concentration fluoride (300mgL−1) have been investigated based on the measurements of polarization curves (PC), cyclic voltammetry (the working electrode was made from pure aluminum, a graphite rod was used as counter and a saturated calomel electrode (SCE) as the reference electrode) and zinc electrodeposition experiments, in which gelatin, boric acid, citric acid and aluminum sulfate served as additives and were added into the electrolytes alone or in combination with different dosages. Zinc deposit morphology on aluminum cathode surface after zinc electrowinning was observed using SEM (scanning electron microscopy). The results indicated that all additives within a certain concentration scope increased nucleation overpotential, stimulated cathodic polarization and promoted electrodepositing with fine-grained zinc. The nucleation overpotential increased from 124mV to 183mV in addition of 5mgL−1. Finer-grained zinc deposits, lower specific power consumption (maximum reduction from 3129 kWht−1 to 2192 kWht−1) and higher current efficiency (86.2% to 96.2%) were available by these additives combination.

Plasma-tolerant structure for organic light-emitting diodes with aluminum cathodes fabricated by DC magnetron sputtering: Using a Li-doped electron transport layer

We fabricate aluminum cathodes that are almost free from plasma damage by DC magnetron sputtering for organic light-emitting diodes (OLEDs). While sputtering is widely known to have numerous advantages over conventional evaporation for mass production of devices, it can cause serious damage to organic layers. In this report, we fabricate devices that are free from plasma damage by introducing a 1%-Li-doped electron transport layer (ETL). The difference of external electroluminescence quantum efficiency between OLEDs with the structure ITO/α-NPD/ETL/Al (where ITO is indium tin oxide and α-NPD is N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine) with Al cathodes deposited by conventional evaporation or sputtering is 0.1%, and their driving voltage is identical. We find that the Li-doped ETL should be thicker than 40nm. Analysis of the depth profile of the ETL by time-of-flight secondary ion mass spectrometry indicates that considerable damage from sputtering extended to a depth of approximately 30nm, suggesting that high-energy particles penetrated about 30nm into the ETL.

Flexible PTB7:PC70BM Bulk-Heterojunction Solar Cells with Lif Cathode Buffer Layer

Bulk heterojunction solar cells were fabricated using [poly[[4,8-bis[(2-ethylhexyl)oxy]benzo [1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]-thiophenediyl] (PTB7) and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) after a layer of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) on a flexible indium tin oxide (ITO)-coated polyethylene terephthalate substrate. The fabricated structures were Al/LiF/PTB7:PC71BM/PEDOT:PSS/ITO with or without a lithium fluoride (LiF) buffer layer, and the influence of the LiF buffer layer on the performance of the solar cells was investigated. The LiF layer significantly enhanced the open-circuit voltages and fill factors of the solar cells presumably because of the work function shift of the aluminum cathode. As a result, the conversion efficiency increased from 2.31% to 4.02% owing to the presence of the LiF layer.

Efficiency enhancement caused by using LiF to change electronic structures in polymer photovoltaics

The enhancement of device performance achieved by inserting a LiF (lithium fluoride) interfacial layer between the active layer and aluminum (Al) cathode was investigated. Energy band diagrams and interfacial chemical reactions were examined using high-resolution synchrotron-radiation photoemission spectroscopy. If only a thin layer of Al is deposited on the P3HT:PCBM/LiF, the highest occupied molecular orbital level of the active layer does not change. This indicates that shifts in the energy band are only strongly influenced by the insertion of LiF, not the subsequent deposition of an Al layer. We found that the molecular energy band shifts occurred at the interface because of the presence of LiF increases the open-circuit voltage. Furthermore, the thin layer of LiF reduces the work function and improves contact with the cathode, thereby reducing the series resistance and improving the short circuit current density. Thus, without the influence of the Al layer, inserting LiF improves the device performance. The level of performance differs substantially from that observed at the organic layer/LiF/Al interfaces in organic light-emitting devices.

GEM-based thermal neutron beam monitors for spallation sources

The development of new large area and high flux thermal neutron detectors for future neutron spallation sources, like the European Spallation Source (ESS) is motivated by the problem of 3He shortage. In the framework of the development of ESS, GEM (Gas Electron Multiplier) is one of the detector technologies that are being explored as thermal neutron sensors. A first prototype of GEM-based thermal neutron beam monitor (bGEM) has been built during 2012. The bGEM is a triple GEM gaseous detector equipped with an aluminum cathode coated by 1μm thick B4C layer used to convert thermal neutrons to charged particles through the 10B(n,7Li)α nuclear reaction. This paper describes the results obtained by testing a bGEM detector at the ISIS spallation source on the VESUVIO beamline. Beam profiles (FWHMx=31mm and FWHMy=36mm), bGEM thermal neutron counting efficiency (≈1%), detector stability (3.45%) and the time-of-flight spectrum of the beam were successfully measured. This prototype represents the first step towards the development of thermal neutrons detectors with efficiency larger than 50% as alternatives to 3He-based gaseous detectors.

Studies of SDX on the Boundary Resistance between Aluminum Current Collectors and Cathode Active Material Layers

We have developed SDX, aluminum foil with a conductive carbon layer, to reduce cell resistance. SDX also showed high rate performances. To reveal that mechanism, we prepared aluminum foil with various chemical forming layers for studying of resistance and compared to two famous theories about conductive mechanism of carbon particles and aluminum foil.

Processing Al-Sc Alloys at Liquid Aluminum Cathode in KF-AlF3 Molten Salt

Al-Sc Alloys have showed many advanced properties for a wide range of engineering applications, which is usually produced using thermal reduction process. This work presents a study on electrochemical preparation of Al-Sc alloys at liquid aluminum cathode in KF-AlF3 (CR=1.3) molten salt at 750℃. Cyclic voltammetry and linear sweep voltammetry were employed to investigate the electrode reaction. The electro-reduction of Sc(III) takes place on the surface of the aluminum liquid cathode at more positive potential values (0.6V) than at the inert Mo cathode. SEM and Inductively Coupled Plasma (ICP) analysis of the product indicated that Al-Sc alloys were made of α-Al and Al3Sc phases; when the anode current density was 0.5~2.0A/cm2, Sc content was 0.44~0.73%. The obtained results show a promising method to make Al-Sc alloy electrochemically.

Fluoride removal from water and wastewater with a bach cylindrical electrode using electrocoagulation

In this study, an electrochemical reactor with a unique design was used for defluoridation. A rotating impeller aluminium cathode and a cylindrical aluminium anode, which until now have not been employed for fluoride removal in the literature, were used, and various operating parameters, such as the electrode material (aluminium and iron), the current density (in the range of 0.5–2mA/cm2), the duration of electrolysis, the supporting electrolyte dosage (in the range of 0.01–0.03M Na2SO4), the initial pH (in the range of 4–8) and the presence of other ions(Ca2+, Mg2+, PO43-, SO42-), were examined to achieve optimal performance of the process. The experimental results revealed that the fluoride removal could be enhanced at pH 6, higher current density and higher electrocoagulation time using aluminium electrode. The presence of Ca2+ and Mg2+ ions also enhanced the removal efficiency while SO42- and PO43- ions effected adversely.The fluoride concentration was reduced from the initial value of 5.0–0.12mg/L, with a removal efficiency of 97.6% after 30min treatment at the current density of 2mA/cm2, pHi of 6 and presence of 0.01M Na2SO4. The required electrocoagulation time to reach the WHO-recommended fluoride limit of 1.2mg/L at 0.5mA/cm2 was 5min, with an energy consumption of 0.47kWh/m3. The obtained results show that this specially designed electrochemical reactor is an efficient alternative for the defluoridation of the water and the wastewater.

Quantification of the Material’s Resistance to Damage by Lightning

The current work undertakes an attempt to establish a methodology towards determination of a universal constant of the material resistance to lightning. A proper quantification of the induced damage will enable a simultaneous comparison among various structural materials based on their dynamic responses in the simulated lightning environment. As an initial approach, evolution of damage was investigated in the lightning quasi electrostatic fields with the ensuing formation of the thermal plasma discharge characterized by the 200–500 A current in the 0.14–3.86 s time range in the unpainted aluminum cathodes at atmospheric pressure in air. Development of damage followed the kinetics law, where the process rate constant, , expressed as a dimensionless quantity of the relative change in damage volume or in material residual ultimate tensile strength, showed independence on current amplitude or material’s thickness with . Comparison of the damage volume and material’s loss through ablation suggested formation of damage as a result of metal melting. Linear dependence of the cathode temperature on arc amplitude at the attachment location revealed proximity to the alloy melting point for the 200 A arcs and temperatures exceeding melting approximately by a 1000 °K for the 500 A currents.