Cathode Active Layer Research Articles

Effect of Chromium Poisoning on Performance of Sr-Doped LaMnO3 (LSM)-Based Cathode in Anode-Supported Solid Oxide Fuel Cells

Ni-YSZ anode-supported planar solid oxide fuel cells (SOFCs), comprised of a Sr-doped LaMnO3 (LSM) + yttria-stabilized zirconia (YSZ) cathode active layer and a LSM cathode current collector layer, are fabricated. Electrochemical performance tests of the cells with and without chromia-forming alloy interconnect in the temperature range 700 - 800°C are conducted. Humidified hydrogen (97% H2 - 3% H2O) is used on the anode side, and oxygen and water vapor contents on the cathode side are varied, in order to control the rate of Cr vaporization. The cathode performances with and without the Cr environment are analyzed by estimating the polarization losses at the cathode. This is done with the help of impedance spectroscopy measurements and curve-fitting the experimentally measured voltage vs current density (V-i) plots to a polarization model. Microstructures of the cathode cross sections are observed before and after the tests to quantify the effects of Cr deposition. Based on these experimental and analytical results, the effects of Cr poisoning on performance of LSM-based cathode under various conditions are evaluated, and mechanisms of Cr poisoning are proposed.

The Mechanism of Decreasing Resistance by SDX™ in Lithium Ion Battery

1. Introduction Practical uses of lithium-ion batteries are rapidly growing especially in large batteries for electric vehicles (EV), energy storage systems (ESS) and so on, but improvements of their characteristics still are strongly demanded. Large improvements of battery characteristics of LFP (LiFePO4) and NMC (LiNi1/3 Mn1/3 Co1/3 O2) as cathode active material, by using ‘SDXTM’ which is a conducting carbon coated aluminum current collector, have been reported [1,2]. The control of internal resistance of lithium ion batteries by the clarification of mechanism of internal resistance is one of the biggest key items to improve them. So the mechanisms of interface resistance between aluminum current collector and cathode active material layer have been investigated and discussed [3]. In the battery which used LFP as cathode active material, recently the quantitative investigation of contribution to electronic resistance reduction of SDXTMand conducting additives was provided by the result of measurement using ELECTRODE RESISTANCE METER (Under development by HIOKI E.E. CORPORATION) which could divide electrode resistance into material resistance and interface resistance (Fig.1). The interface resistance of the cathde with aluminum current collectors was higher than the material resistance of that by almost one order of magnitude. The interface resistance of the cathode with SDXTMwas lower than that with aluminum current collectors by almost one order of magnitude. Because the interface resistance was reduced by SDXTM, it was reported that conducting additives were able to be reduced much in cathode [4]. In this paper, more detailed examination will be carried out, and the effect of SDXTMin lithium ion battery will be tried to be clarified. 2. Experiment The preparation of electrode slurry was carried out by dispersing LFP as cathode active material, conducting additives and polyvinylidene difluoride (PVdF) into N-methylpyrrolidone (NMP). Cathode electrodes were prepared by coating the slurry onto SDXTM or aluminum current collectors in several coating speeds (e.g. 300, 400 or 500mm/min), by drying and by pressing them. Artificial graphite (SCMGTM) was used for anode active material, and similarly anode electrodes were prepared by coating its slurry (aqueous solution) onto copper current collectors, by drying and by pressing them. By laminating one sheet of anode and one sheet of cathode, pouch type cell was assembled. 3. Results and discussion The material resistance and the interface resistance of the cathode were measured by ELECTRODE RESISTANCE METER (Fig.2). In each coating speed, the interface resistance of the cathode with aluminum current collectors was higher than the material resistance of that. The interface resistance of the cathode with SDXTM was lower than that with aluminum current collectors, and it was almost same as the material resistance of the cathode with SDXTM. The interface resistance of the cathode with aluminum current collectors increased when the coating speed increased, but the interface resistance of the cathode with SDXTMwas constant without depending on coating speed. Cell DCRs were measured (Fig.3). The cell DCR with aluminum current collectors increased when the coating speed increased, but the cell DCR with SDXTMwas constant without depending on coating speed. It was confirmed that the cell DCR with aluminum current collector showed similar behavior to the interface resistance of the cathode with aluminum current collector. The visualization results of a dispersion state of conducting additive in an electrode will be presented.

Engineering the solid oxide fuel cell electrocatalyst infiltration technique for industrial use

In this work, we explore various parameters for infiltrating La0.6Sr0.4CoO3-δ (LSCo) into the La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) – Ce0.8Sm0.2O2 (SDC) cathode of a planar solid oxide fuel cell (SOFC) using an automated solution dispensing technique for commercial deployment of infiltrated SOFCs by industry. Substrate temperature, chelating agent concentration, and surfactant type were explored to develop a 1-step infiltration process for delivering 8–10 weight percent of LSCo electrocatalyst to the cathode active layer. The results confirm increased fuel cell performance and durability by optimizing the infiltrate solution for increased transport into the cathode's microstructure.

Aqueous Solution Processed Photoconductive Cathode Interlayer for High Performance Polymer Solar Cells with Thick Interlayer and Thick Active Layer.

An aqueous-solution-processed photoconductive cathode interlayer is developed, in which the photoinduced charge transfer brings multiple advantages such as increased conductivity and electron mobility, as well as reduced work function. Average power conversion efficiency over 10% is achieved even when the thickness of the cathode interlayer and active layer is up to 100 and 300 nm, respectively.

ACTIVE LAYER OF FUEL CELL CATHODE WITH POLYMER ELECTROLYTE: COMPUTER SIMULATION PROCESS OF MOISTURE EXCHANGE IN SUPPORT GRAINS

In the cathode active layer of a fuel cell with a solid polymer electrolyte process, the current generation takes place in support grains (agglomerates of carbon particles with supported platinum). The speed of this process essentially depends on a degree of support grains pores filling with water. Calculations show if support grains pores are completely filled with water the overall current density in the cathode active layer is much less than in the case of the pores partially or even completely free of water. The last variant of a cathode active layer functioning is realized when the release rate of pores from moisture due to evaporation and filtration of water exceeds the rate of flooding process of ones with water in the process of current generation. This study by method of computer simulation presents a specific example of determining the overall current density in the cathode active layer with varying the speed of emptiness process in pores from moisture due to filtration.

COMPUTER SIMULATION OF ACTIVE LAYER FUEL CELL WITH POLYMER ELECTROLYTE: СОNNECTION OVERALL CURRENT WITH TEMPERATURE OF ACTIVE LAYER

In the cathode active layer of a fuel cell with a solid polymer electrolyte process of current generation takes place in support grains. The speed of this process essentially depends on a degree of support grains pores filling with water. Calculations show, if support grains pores are completely filled with water, the overall current value in the cathode active layer much less rather in the case when pores partially or even completely free of water. The last variant of a cathode active layer functioning is realized when the speed of emptiness process in pores from moisture due to evaporation exceeds the rate of flooding process of ones with water in the process of current generation. To increase the overall current is possible by increasing a degree of heating-up of the cathode active layer. It is desirable that the temperature of the active layer Ts as much as possible exceed the temperature T, which the fuel cell operates. In this study by method of computer simulation a specific example of determining the overall current value in the cathode active layer is presented. It is shown how overall current increase if magnify difference of temperature Ts–T.

Building thermally stable Li-ion batteries using a temperature-responsive cathode

A temperature-responsive cathode is developed by coating an ultra-thin layer of poly(3-octylthiophene) in between an Al substrate and cathode-active layer.

COMPUTER SIMULATION OF ACTIVE LAYER FUEL CELL WITH POLYMER ELECTROLYTE: HOW DEGREE FILLING OF SUPPORT GRAIN BY WATER INFLUENCES ON OVERALL CURRENT

In the cathode active layer of a fuel cell with a solid polymer electrolyte, process of current generation takes place in support grains. The speed of this process essentially depends on a degree of support grains pores filling with water. Calculations show that the overall current value in the cathode active layer with the pores of support grains completely filled with water are much less than with pores partially filled or even without water. The last variant is realized when the rate of moisture evaporation from the pores of the support grains exceeds the rate of flooding them in the current generation process. In order to increase the overall current, a degree of heating-up of the cathode active layer is necessary to increase. It is desirable that the temperature of the active layer T s as much as possible exceed the temperature T , which the fuel cell operates. In this study by method of computer simulation, a specific example of determining the overall current value in the cathode active layer is presented. It is shown that if the pores of support grains are completely filled with water, then overall current I = 0.223 A/cm 2 , and if the pores of the support grains are filled with water only about 10 percent then I = 1.151 A/cm 2 .

High Detectivity All-Printed Organic Photodiodes.

All-printed organic photodiode arrays on plastic are reported with average specific detectivities of 3.45 × 10(13) cm Hz(0.5) W(-1) at a bias of -5 V. The blade-coated polyethylenimine cathode interlayer and active layer, and screen-printed anode enable precise device performance tunability and excellent homogeneity at centimetric scales. These devices' high operational reverse bias, good linear dynamic range, and bias stress stability make them attractive for implementation in imaging systems.

Rational design of metallic nanowire-based plasmonic architectures for efficient inverted polymer solar cells

Plasmonics can improve the performance of polymer solar cells (PSCs) by localizing and concentrating light, and the location of the plasmonic metallic nanostructure in devices plays an important role in how to design high-performance plasmonic solar cells. Here, by varying the location of silver nanowires (Ag NWs) within the device architecture (at the interface between indium–tin–oxide and cathode buffer layer, cathode buffer layer and active layer, active layer and anode buffer layer, respectively), a systematic study on plasmonic effect on the properties of photovoltaic material was presented. The density of photogenerated excitons, the electron delocalization and the effective conjugation length of the photovoltaic material in our pre-designed plasmonic structures were increased, and the enhancements of plasmonic effects were effective in a broad spectral range. When the pre-designed plasmonic structures were incorporated into the inverted PSCs, short circuit current density (Jsc) for all the investigated structures showed increase. The optimal inverted device performance was achieved when the Ag NWs were located at the interface of indium–tin–oxide and cathode buffer layer. The power conversion efficiency of the optimized plasmonic inverted device reached 4.05% under AM1.5 illumination (100 mW/cm2), which was due to the enhancement of Jsc without reducing the open-circuit voltage and FF of the plasmonic inverted PSCs by introducing Ag NWs.

Various Scales of Aging Heterogeneities upon PEMFC Operation – A Link between Local MEA Materials Degradation and the Cell Performance

It is no secret that PEMFC performances decay upon operation, owing to the degradation of their core materials 1. Refining the data obtained from several experimental campaigns made in close collaboration between Axane and academic laboratories, it soon appeared that the materials degradations were not homogeneous within a PEMFC, whatever its operating conditions (stationary on the field or accelerated stress test at the laboratory scale) and their constitutive materials. If one limits to the cathode active layer, there are three distinct levels of degradation heterogeneities. (i) At the scale of the MEA, the degradations are neither homogeneous along the gas channels of the bipolar plates (BP, from the inlet to the outlet, Figure 1) 2, nor along the active layer thickness (from the membrane interface to the diffusion layer interface) 2,3. (ii) The BP geometry also matters, since in the particular case of repeated start/stop and associated fuel-starvation events, harsher degradation was observed for the cathode regions facing the anode regions located under the land of the BP (Figure 2) 4. (iii) Finally, not all the cells operate and age in the same manner at the stack level (Figure 3) 5. In any case, the degradations are strongly linked to the materials composing the MEA, but also depend on the fluidics of the cell (e.g. design of the bipolar plates and stack), which renders difficult any generalization of the conclusions obtained for a particular test. References (1) Gasteiger, H. A.; Vielstich, W.; Yokokawa, H. Handbook of Fuel Cells; John Wiley & Sons Ltd: Chichester, 2009; Vol. 5-6. (2) Dubau, L.; Durst, J.; Maillard, F.; Chatenet, M.; Guétaz, L.; André, J.; Rossinot, E. Fuel Cells 2012, 12, 188. (3) Ferreira, P. J.; la O', G. J.; Shao-Horn, Y.; Morgan, D.; Makharia, R.; Kocha, S.; Gasteiger, H. A. J. Electrochem. Soc. 2005, 152, A2256. (4) Durst, J.; Lamibrac, A.; Charlot, F.; Dillet, J.; Castanheira, L. F.; Maranzana, G.; Dubau, L.; Maillard, F.; Chatenet, M.; Lottin, O. Appl. Catal. B: Environmental 2013, 138-139, 416. (5) Dubau, L.; Castanheira, L.; Maillard, F.; Chatenet, M.; Lottin, O.; Maranzana, G.; Dillet, J.; ElKaddouri, A.; Basu, S.; De Moor, G.; Flandin, L.; Caqué, N. Int. J. Hydrogen Energy 2014, 39 21902 Figure 1

Electrochemical and structure characteristics of PtCoCr/C-Catalyst with platinum content 50 wt % and cathode on its basis for fuel cell with proton-conducting polymer electrolyte

Electrochemical and structure characteristics of PtCoCr/C-catalyst with platinum content 50 wt % under model conditions and in cathode of membrane-electrode assembly (MEA) of hydrogen-oxygen fuel cell are studied. The metal-phase nanoparticles are shown to represent a Pt3Co alloy with partial inclusion of chromium, the nanoparticles surface being enriched with platinum. The platinum mass activity and the PtCoCr/C-catalyst high corrosion resistance do not depend on the amount of platinum deposited onto XC72 carbon black (20 or 50 wt %). Herewith the platinum surface area decreases in the same way as the carbon black specific surface area (measured with the BET method); the latter is 227, 169, and 105 m2/g for pure carbon black and that containing 20 and 50 wt % Pt, respectively. Testing of the 50PtCoCr/C-catalyst in the MEA cathode active layer in hydrogen-oxygen fuel cell showed performance not inferior to MEAs with pure-platinum systems, the catalyst being more stable.

Chemical and microstructural transformations in lithium iron phosphate battery electrodes following pulsed laser exposure

Multi-layer lithium iron phosphate (LFP) battery electrodes are exposed to nanosecond pulsed laser radiation of wavelength 1064nm. Test parameters are chosen to achieve characteristic interaction types ranging from partial incision of the active coating layers only to complete penetration of the electrodes with high visual cut quality. Raman spectroscopy is performed on unexposed regions and at points approaching each incision, highlighting changes in chemical composition and microstructure in the heat affected zone (HAZ). Thermogravimetric analysis is performed on the unexposed electrode active materials to distinguish the development of compositional changes under conditions of slow heating below the melting and sublimation temperatures. A brief theoretical description of the physical phenomena taking place during laser exposure is provided in terms of direct ablation during each laser pulse and vaporization or thermal degradation due to conductive heat transfer on a much longer time-scale, with characteristics of the HAZ reported in terms of these changes. For all laser exposures carried out in the study, chemical and microstructural changes are limited to the visible HAZ. Some degree of oxidation and LFP olivine phase degradation is observed in the cathode, while the polycrystalline graphite structure becomes less ordered in the anode. Where complete penetration is achieved, melting of the cathode active layer and combustion of the anode active layer take place near the cut edge due to thermal conduction from the metallic conductive layers. The presented results provide insight into the effects of laser processing on LFP electrode integrity.

Rapid diagnostics of characteristics and stability of fuel cells with proton-conducting electrolyte

Processes underlying the degrading of membrane-electrode assemblies of hydrogen-air fuel cells with Nafion 212 and MF-4SK membranes under the conditions of their accelerated stress testing and long-term life tests are analyzed. The cathode platinum catalyst corrosion was shown to be the main cause of the degrading of the fuel cell’s kinetically controlled current-voltage characteristics; the corrosion is accompanied by the platinum nanoparticles’ growth and the platinum ion partial transfer into the membrane. The overvoltage components of the membrane-electrode assembly and their changing during accelerated stress testing are determined. The voltage decrease at currents >0.5 A/cm2 is shown to be mainly caused by the transport and ohmic resistance growth. The transport resistance components are calculated; the dependence of the cathode active layer resistance on the platinum catalyst surface area is revealed.

Study of degradation of membrane-electrode assemblies of hydrogen-oxygen (air) fuel cell under the conditions of life tests and voltage cycling

The degradation processes of HiSPEC 9100 (60% Pt/C) and 13100 (70% Pt/C) cathodic monoplatinum catalysts, which were tested under the model conditions and in the composition of membrane-electrode assemblies (MEA) of hydrogen-air and hydrogen-oxygen fuel cells, are studied. It is shown that, in all cases, the main reason for a decrease in the catalyst activity was a decrease in its surface area, which was caused by the coarsening of platinum nanoparticles, irreversible oxidation of a fraction of active centers, and the destruction of the catalyst due to the carbon support oxidation. The results of electrochemical measurements are supplemented with the structural investigations by the methods of transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), and X-ray photoelectron spectroscopy (XPS). It is found that the degradation processes of MEA in the accelerated stress tests (AST) are similar to those in the long-term life tests. With respect to a decrease in the catalyst active surface area, the application of 2500 cycles in the voltage range of 0.6 to 1.2 V in the AST is equivalent to the life tests for 1010 h. During the fuel cell operation, the destruction of polymer electrolyte proceeds along with the catalyst degradation. This leads to a decrease in the ion-exchange capacity of the membrane and ionomer in the composition of cathode active layer.

Infiltrated porous YSZ as a cathode active layer for cathode-supported solid oxide fuel cells

A novel active cathode structure of La0.6Sr0.4Fe0.9Sc0.1O3−δ (LSFSc) infiltrated porous 8mol% Y2O3-stabilized ZrO2 (YSZ) was fabricated by tape casting, co-sintering and infiltration techniques. The infiltrated porous-YSZ layer worked as a cathode active layer (CAL) between a YSZ electrolyte layer and (La0.8Sr0.2)0.95MnO3 (LSM95) cathode substrate. The obtained fuel cells with Ni/SDC anode showed the maximum power densities of 0.574, 0.733 and 0.835W·cm−2 at 750, 800 and 850°C, respectively, with H2 as fuel and air as the oxidant.

An algorithm for diagnosis of proton exchange membrane fuel cells by electrochemical impedance spectroscopy

Further analysis of EIS provides valuable information about reliability and aging of the systems, namely to diagnose water flooding the electrode or membrane drying for Proton Exchange Membrane Fuel Cells (PEMFC). The aim of this study is to propose an electrochemical parameter fitting algorithm. A careful study of the electrochemical kinetics laws allowed us to demonstrate that, as long as both electrodes follow a Tafel behavior, the cathode and anode active layer resistances are strongly correlated. This correlation obviously removes a liberty degree in the model and allow an accurate fitting of the utilized model's electrochemical parameters of our PEMFC stack EIS. The reduced number of liberty degrees eases the convergence of the solution of the model. This algorithm was successfully implemented on different PEMFC stacks technology to investigate the impact of water flooding and the operating points.

One-Step Flash Sintering of Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are ideally suited for environmentally benign conversion of chemical energy in hydrocarbons to electricity. While medium scale SOFC power systems in the hundreds of kWe have been demonstrated, larger scale application of such systems have been hobbled by still too high cost. Reducing the manufacturing costs of single cells is an important goal as one step towards commercialization. Previously, we demonstrated a simplified process to manufacture the complex multilayer architecture of anode supported single cells in a single high temperature firing step, after deposition of the anode active layer, electrolyte, cathode active layer, and cathode current collector layers serially by screen printing on to an anode substrate fabrication by a process known as high shear compaction. In this paper, we present a novel manufacturing process in which the basic green-state cell is fabricated using the same steps as before, but in which the high temperature conventional sintering step is replaced by a technique known as flash sintering which reduces time at temperature by up to an order of magnitude, thereby resulting in significant savings in time and electrical energy expended. We present details of this new process, cross-sectional microstructures of cells fabricated using this technique, and compare the power densities of the cells processed by flash sintering with the prior co-fired process.

Transition metal-doped yttria stabilized zirconia for low temperature processing of planar anode-supported solid oxide fuel cell

An attempt has been made to reduce the processing temperature for fabrication of anode-supported solid oxide fuel cell using transition metal doped 8mol% yttria stabilized zirconia (YSZ) as the material for electrolyte and Ni-YSZ anode support. Through a simple mixing technique, the sintering temperature of a widely used commercial YSZ powder is possible to reduce substantially by adding 2mol% transition metal oxides e.g. cobalt, manganese and iron. More than 96% of theoretical density is achieved at 1175°C. No difference in thermal expansion behaviour is observed for the doped YSZ with respect to pure YSZ (without any additive). Using tape casting and lamination techniques, planar anode-supported half cells (Ni-YSZ/YSZ) were fabricated with such doped YSZ and co-sintered at two different temperatures viz., 1175°C and 1350°C. Finally, single cells (dia. ∼15mm) were fabricated through screen printing of La(Sr)MnO3 (LSM)–YSZ based cathode active layer and LSM current collector layer and tested with hydrogen as fuel and oxygen as oxidant in the temperature range 700–800°C. A reasonably good electrochemical performance (∼1.6A/cm2 at 0.7V and 800°C) is achieved for single cells when half-cell sintering temperature is 1350°C. However, under identical conditions, the current density dropped below 0.2A/cm2 when the corresponding half-cell is sintered at 1175°C. For such a cell, although the open circuit voltage (OCV) is found to be very stable (∼1.1V), the current drawing capability fell abruptly with increasing current load and a corresponding decrease of cell voltage. The cell microstructure revealed that while sintering half-cell at 1175°C, complete densification of the doped YSZ electrolyte film is not achieved. It is anticipated that redesigning of fabrication steps could be required to utilize the benefits of low sintering temperature of cell components.

Direct foamed and nanocatalyst impregnated SOFC cathodes

A binder system containing polyurethane precursors was used to in situ foam (direct foam) an (La 0.6 Sr 0.4 ) 0.98 (Co 0.2 Fe 0.8 )O 3−δ (LSCF) cathode composition on an yttrium-stabilised zirconia (YSZ) electrolyte coated with a porous ∼10 µm thick cathode active layer. The YSZ electrolyte was ∼110 μm thick, and a fuel cell was created by application of a Ni/(Ce 0.9 Gd 0.1 )O 2 cermet as the baseline anode. Cells possessing the foamed LSCF cathode were compared to cells constructed via standard methods in terms of resultant microstructure, electrochemical performance, and introceptive character. The foamed cathode tended to possess a high level of tortuous porosity which was ellipsoidal and interconnected in character. Both the standard and foamed cathode structures were subjected to an infiltration process, and the resultant microstructure was examined. The impregnation efficiency of the foamed cathode was at least ∼10% greater per deposition than that of an unfoamed porous LSCF cathode. The SOFC with the Pt nanocatalyst impregnated foamed cathode demonstrated a maximum power density of 593 mW/cm 2 utilising wet H 2 fuel, which is 52% higher than an SOFC with the baseline Pt-impregnated LSCF cathode (∼390 mW/cm 2 ) at 800°C. The cathode compositional and microstructural alterations obtainable by foaming led to the elevated power performance, which was shown to be quite high relative to standard SOFCs with a thick YSZ electrolyte.