Manganite Cathode Research Articles

Solid Oxide Fuel Cells with 3D Inkjet Printing Modified LSM-YSZ Interface

In this study, pillar shaped yttria-stabilized zirconia (YSZ) 3D microstructures with ∼60 to 90 μm diameter and 12 to 20 μm height are fabricated by 3D inkjet printing to improve the topology of the electrolyte/cathode interface. The microstructures increase the surface area of the cell by ∼2.4% to 4.0% and enhance the connection between the dense YSZ electrolyte and mixed YSZ-lanthanum strontium manganite (LSM) cathode. The morphology and microstructure of the YSZ interface are characterized with scanning electron microscopy. Polarization curves confirm that the power density improves by 47% to 107% at 0.55 V, depending on the dimensions of the microstructures, in comparison to a flat interface. The non-linear improvement in power density with the size of microstructures is confirmed by calculating the uncertainty with repeated tests. Based on electrochemical impedance spectroscopy and distribution of relaxation times analysis, the performance improvement is attributed to changes in the oxygen surface exchange kinetics and O2− diffusivity in the cathode.

Colloidal Processing of Y0.08Zr0.92O2/La0.80Sr0.20MnO3 Semi-Cells Using a Sr-Doped Lanthanum Manganite Synthesized by a Citrate Route.

In this paper, the interface between yttria stabilized zirconia (Y0.08Zr0.92O2, YSZ) electrolyte and Sr-doped lanthanum manganite (La0.80Sr0.20MnO3, LSM) cathode for solid oxide fuel cells (SOFCs) is studied. For such a purpose, the combination of a suitable synthesis route for obtaining fine powders and simple aqueous colloidal shaping routes is proposed. The synthesis of nanosized particles of La0.80Sr0.20MnO3 by a citrate route and their full characterization, including the colloidal stability and the densification and phase development determined by X-ray diffraction and electron microscopy at different temperatures, is reported. In a second step, YSZ tapes were obtained by aqueous tape casting and used as substrates for the preparation of LSM coatings by dip-coating using aqueous slurries. YSZ tapes were used either in the green state or after a pre-sintering treatment. Co-sintering at 1350 °C led to a sharp interface with excellent adhesion, also achieved when coating pre-sintered tapes. In both cases, the substrates are dense and the coatings are porous, with thicknesses of 85 and 60 μm for green and pre-sintered tapes, respectively. No diffusion of Zr and Y occurs at the LSM layer, but some diffusion of La and Mn towards the YSZ layer takes place.

Investigation of the Cr volatilisation using the ceramic phase collector technique

An effect of chromium contamination in the lanthanum strontium manganite (LSM) cathode which is a component of solid oxide fuel cell (SOFC) leads to degradation of the device. This is caused by volatilisation of Cr-species from the iron-chromium alloy at high temperature. In this work, the ceramic phase collector technique was used to evaluate the Cr volatilisation. To prove the effectiveness of this method, AISI 430 ferritic stainless steel samples with and without cobalt (Co) spinel coatings were used to compare the Cr condensation in the LSM ceramic. The coatings were produced by electroplating followed by a heat-treatment process. The samples were characterised using SEM with EDX and XRD to confirm the microstructure and the formation of Co spinel. It was found that chromium migration was restrained for coated samples, in contrast the Cr-species deposited in the LSM for uncoated samples. The chromium volatilisation evaluated by the contents of Cr species in the LSM collector was compared to the traditional condensation technique which analysed chemical contents by inductively coupled plasma-mass spectrometry (ICP-MS).

Investigating Effects of Operational Parameters on the Rate of Electrochemical Cleaning of Chromium Deposits on Strontium-Doped Lanthanum Manganite Cathodes in Solid Oxide Fuel Cells

Chromium poisoning of the cathode remains a significant obstacle to the long-term performance of solid oxide fuel cells. Previously, a quick, easy method was introduced that requires no material modifications, major thermal cycling, nor exposes the cell to any species it does not already encounter during operation. The method, electrochemical cleaning, reverses the electrochemical deposition reaction of chromium-containing species by applying a mild anodic bias. Chromium vapor species are formed, freeing active sites in the cathode. The method has been shown to completely recover cell performance via this current-voltage technique.The present work investigates the mechanism of electrochemical cleaning by assessing the effect of various operating parameters on the rate of chromium removal. Using a design of experiments method, eight cells were poisoned and then cleaned using differing combinations of the following cleaning parameters: cell temperature, air humidity, anodic current density, and fuel humidity. Regression analysis of two comparative metrics, cell performance via current voltage curves and post-test chromium content determined via Energy Dispersive Spectroscopy, demonstrated that cell temperature has the highest effect on the rate of chromium removal, followed by air humidity. A refined parameter space for future study is proposed for further optimization of the parameters. Previously, the electrochemical cleaning method was shown to be effective in the removal of Cr2O3 deposited species, but not Cr-Mn spinel deposits. The effects of operating parameters on the removal of the two different types of Cr deposits is discussed. An additional process for the removal of Cr-Mn spinel is demonstrated, which again makes use of the cell operating parameters. Together, the two methods present a facile, periodic process to greatly extend solid oxide fuel cell lifetime.

Investigating Effects of Operational Parameters on the Rate of Electrochemical Cleaning of Chromium Deposits on Strontium-Doped Lanthanum Manganite Cathodes in Solid Oxide Fuel Cells

Chromium poisoning of the cathode remains a significant obstacle to the stable long-term performance of solid oxide fuel cells. This study reports, a quick, in-situ mitigation method, called electrochemical cleaning. By applying a mild anodic bias, the electrochemical deposition reactions of chromium-containing species are reversed. Chromium vapor species are formed, freeing active electrochemical sites in the air electrode. An LSM/YSZ-based cell was exposed to Cr vapors at 800ºC and then subjected to electrochemical cleaning. Cell performance recovery was evidenced by current-voltage and EIS measurements. Chromium removal was verified using SEM and EDS analyses. The cyclability of the electrochemical cleaning was tested by repeated poisoning and cleaning of another cell. Investigation into the effect of cell operating parameters (current density and cell temperature) on the rate of cleaning is discussed.

Corrigendum: Aqueous Calcium‐Ion Battery Based on a Mesoporous Organic Anode and a Manganite Cathode with Long Cycling Performance

During preparation of the version of record of the above manuscript, Figure 3 was duplicated as Figure 6. The correct Figure 6 is as follows: Figure 6. Typical CV curves of individual electrodes and typical charge–discharge curves of the aqueous Ca-ion cell based on SBA-15@PPTCDI‖Ca2MnO4: a) CV curves of SBA-15@PPTCDI as the anode, Ca2MnO4 as the cathode, and the SBA-15@PPTCDI‖Ca2MnO4 full cell at a scan rate of 0.5 mV s−1. b) Typical charge–discharge curves of the aqueous Mg-ion cell based on SBA-15@PPTCDI as the anode, Ca2MnO4 as the cathode, and SBA-15@PPTCDI‖Ca2MnO4 as the full cell at a current density of 100 mA g−1, based on cathode/anode weight. c) Galvanostatic charge–discharge curves at several current densities between 0 and 1.80 V. d) Ragone plot of the SBA-15@PPTCDI‖Ca2MnO4 cell. e) Cycling and coulombic performance of an aqueous CIB. f) A comparison to other previously reported CIBs or nonaqueous battery systems. This correction has no influence on the scientific content. The editorial office apologizes for this oversight and for any inconvenience caused.

Water cointercalation for high-energy-density aqueous zinc-ion battery based potassium manganite cathode

Aqueous zinc-ion batteries (ZIBs) are gaining widespread attention owing to their intrinsic safety and low cost. However, it is still a challenge that finding robust cathode materials to build a high-energy-density aqueous ZIBs. Here, we synthesize a novel layered K0.41MnO2·0.5H2O (KMO) cathode material for aqueous ZIBs. The constructed Zn//KMO battery shows an ultrahigh discharge capacity of 425 mAh g−1 and a remarkable energy density of 503 Wh kg−1 at 175 mA g−1, as well as an good durability over 1500 cycles with no obvious capacity fading. A comprehensive study suggests that the water molecules can intercalate into layered KMO with H+ and Zn2+ ions during discharging process. The co-intercalating water not only facilitates ions insertion, but serves as pillars to stabilize the structure of KMO. This work demonstrates the mechanism about water cointercalation and provides a way for designing high-energy-density aqueous ZIBs.

A solid oxide fuel cell with molten tin anode for electricity generation and methane reforming

A methane-fuelled solid oxide fuel cell (SOFC) with molten tin anode (Sn(l)-SOFC) is designed, fabricated, demonstrated and characterized. This SOFC design incorporates molten tin contained in an alumina crucible as anode for the solution of oxygen atoms transported to an anode | Yttria stabilized Zirconia (YSZ) electrolyte interface and provides bubble | molten tin interfaces for the reaction of methane with oxygen atoms during cell operation. A peak power density of ca. 100 W m−2 at a current density of 222 A m−2 and potential difference of 0.45 V is obtained for this methane-fuelled Sn(l)-SOFC at 850 °C. The ohmic and non-ohmic impedance are ca. 16.72 and 3.36 Ω cm2, respectively. Ohmic potential losses control the reactor performance, with about ca. 59% of those arising from the inherent difficulty in achieving a low resistance contact at the silver wire (silver wool) current collector | Lanthanum strontium manganite cathode interface. Improved performance is achievable by eliminating contact resistance, utilising a molten metal/alloy with greater activity for methane oxidation and operating the cell at higher temperatures. The reaction of methane at bubble | molten tin interface involves its coupling in addition to oxidation, to produce steam, carbon dioxide, hydrogen, ethane and ethylene.

Aqueous Calcium-Ion Battery Based on a Mesoporous Organic Anode and a Manganite Cathode with Long Cycling Performance.

Aqueous batteries have attracted increasing and extensive attention, owing to their high safety, low cost, and low toxicity. These factors have become increasingly important, given the current focus on the rapid development of green energy technologies. In particular, multivalent-ion batteries are emerging as alternatives to lithium-ion batteries. Unfortunately, magnesium and aluminum ions have high polarization strengths that are unfavorable for electrode materials. In contrast, calcium-ion batteries successfully avoid the problem of high polarization. Herein, an aqueous calcium-ion battery (CIBs) based on mesoporous silica SBA-15 with a two-dimensional hexagonal through-hole structure is reported. The poly(3,4,9,10-perylentetracarboxylic diimide) (PPTCDI) organic material supported on SBA-15 is used as the anode and displays a capacity of 201 mAh g-1 , with a stable cycling performance of 95 % capacity retention after 1500 cycles. SBA-15@PPTCDI‖Ca2 MnO4 aqueous CIBs demonstrate a high energy density of 130.6 Wh kg-1 in the cell voltage range from 0.0 to 1.8 V, with a high capacity and excellent cycling stability. As the anode material, SBA-15@PPTCDI shows special bonding of redox electrons that leads to its highly stable performance, which paves the way for addressing the shortcomings of traditional organic electrode materials. The localization and delocalization of the redox electron offers additional voltage stability, which is another important advantage for practical applications. This study highlights the potential of organic electrode materials for applications in aqueous multivalent-metal-ion batteries.

Improving fuel cell performance via optimal parameters identification through fuzzy logic based-modeling and optimization

Improving the performance of solid oxide fuel cell via maximizing its available peak power density is a key requirement of research in the field of renewable energy. This could be achieved through identifying the optimal controlling parameters such as, the deposition instrument power (P), the temperature (T), and the electrolyte thickness (Thick). Nickel–Gadolinium Doped Ceria cermet anode films are deposited on one side of the Zirconia electrolyte by radio frequency sputtering. The sputtering plasma power is varied at 50, 100, 150, and 200 W. Lanthanum Strontium Manganite cathodes were screen-printed on the other side of the electrolyte supports to complete the configuration. Cells were electrochemically tested at various intermediate solid oxide fuel cell temperatures of 600, 700 and 800 °C using different electrolyte thicknesses. The cell’s current density, I (A/cm2) and voltage (V) and hence the power density (W/cm2) are recorded in each case. Based on the obtained experimental results, a fuzzy model is built using different control parameters. Then, the particle swarm optimization technique is used for obtaining the best parameters of the cell that maximizes its power density. The results show that by utilizing the optimized conditions, the power density can be increased to 0.39 (W/cm2), which is almost two times higher than the maximum power density obtained experimentally.

Improved Tolerance of Lanthanum Nickelate (La2NiO4+δ) Cathodes to Chromium Poisoning Under Current Load in Solid Oxide Fuel Cells

Lanthanum nickelate, La2NiO4+δ (LNO), is studied as a cathode material for use in solid oxide fuel cells with the objective of mitigating chromium poisoning. Under current load, both electrochemical and chemical reactions cause chromium poisoning, and high current density and humidity accelerate the poisoning. However, compared with a standard strontium-doped lanthanum manganite cathode, the LNO cathode has a much higher tolerance for chromium poisoning. This can be ascribed to a greatly reduced chromium deposition in LNO.

Composition-gradient protective coatings for solid oxide fuel cell interconnectors

Protective Ni-based coatings for stainless steel current collectors of the planar solid oxide fuel cells (SOFCs) were developed and tested during 21,000 h in contact with lanthanum-strontium manganite cathode material. The compositional and microstructural alterations due to interdiffusion between Ni coating, La0.8Sr0.2MnO3 electrode and commercial Crofer 22 APU steel after long-term testing under the SOFC cathodic conditions, were studied. The results of micro-Raman spectroscopy and electron microscopy analyses showed a dominant role of Mn and Fe diffusion into the protective coating, leading to the formation of NiFe2O4 and MnFe2O4. Although Mn deficiency in the manganite cathode may decrease electrical conductivity, its impact on the overall contact resistance is insignificant. The Ni-based coatings were found to decrease area-specific interfacial resistivity down to 3–4 mOhm × cm2 for, at least, 21,000 h (>2.5 years) at 1123 K, atmospheric oxygen pressure and current density of 0.5 A/cm2.

Reduction of $$\hbox {CO}_{2}$$ CO 2 to CO in presence of $$\hbox {H}_{2}$$ H 2 on strontium doped lanthanum manganite cathode in solid oxide electrolysis cell

Electrochemical performance of $$\hbox {La}_{0.8}\hbox {Sr}_{0.2}\hbox {MnO}_{3-\delta }$$ (LSM) for $$\hbox {CO}_{2}$$ reduction in solid oxide cell is studied by performing impedance spectroscopy measurement and current-voltage characterizations for varying ratio of $$\hbox {CO}_{2}/\hbox {H}_{2}$$ . Ohmic resistance $$(\hbox {R}_{\Omega })$$ is observed to be slightly increased from 2.59 to $$2.70\, \Omega \hbox { cm}^{2}$$ , however; the cathode polarization resistance $$(\hbox {R}_{2})$$ decreased significantly from 16.20 to 4.70 $$\Omega \hbox { cm}^{2}$$ as the $$\hbox {H}_{2}$$ percentage increased from 8 to 82%, respectively. As the $$\hbox {H}_{2}$$ content increased in feed gas, the improved polarization resistance indicated an enhanced activity of LSM for $$\hbox {CO}_{2}$$ reduction reaction. Furthermore, the cathode polarization resistance for $$\hbox {CO}_{2}/\hbox {H}_{2}$$ of 92/08, is observed to be decreased from 16.20 $$\Omega \hbox { cm}^{2}$$ (OCV 0.89 V) to 1.90 $$\Omega \hbox { cm}^{2}$$ (2.0 V) as the applied potential increased in the electrolysis mode of operation. A maximum conversion of $$\hbox {CO}_{2}$$ of 6.0% with 55% of faradaic efficiency for the production of CO is achieved for $$\hbox {CO}_{2}/\hbox {H}_{2}$$ ratio of 38/62, which is supported by improved current-voltage polarization, i.e., an increase in reduction current from $$-0.28$$ to $$-0.32\hbox { A cm}^{-2}$$ (at 2.5 V) as the $$\hbox {CO}_{2}/\hbox {H}_{2}$$ ratio decreased from 92/08 to 38/62 respectively. These results demonstrate LSM as an active electrocatalyst to reduce $$\hbox {CO}_{2}$$ , which could further be improved by increasing the $$\hbox {H}_{2}$$ concentration in the feed composition to the cathode. Synopsis: Solid oxide cell is fabricated with strontium doped lanthanum manganite electrodes and yttria stabilized zirconia electrolyte. Electrochemical performance in terms of impedance spectroscopy and current-voltage characteristics of the cell are reported for the reduction of carbon dioxide into carbon monoxide in presence of hydrogen with varying ratio of $$\hbox {CO}_{2}/\hbox {H}_{2}$$ .

The investigation of Cr deposition and poisoning effect on Sr-doped lanthanum manganite cathode induced by cathodic polarization for intermediate temperature solid oxide fuel cell

The impact of current density on Cr-poisoning of Sr-doped lanthanum manganite cathode is studied at 750°C. The presences of SUS430 interconnect alloys cause rapid degradation in LSM cathode performance. The Cr deposits can be found not only on the LSM surface close to the electrode/electrolyte interface, but also on the YSZ surface. The deposition area is reach to 4.1μm from the electrode/electrolyte interface after cathodic polarization with a current density of 400mAcm−2 for 1200min. TEM results clearly demonstrate that the particles on LSM surface are MnCr2O4 spinels, which means that the Cr species would react with Mn from LSM and then lead to the structural damages of LSM cathode. A high polarization current of 800mAcm−2 significantly accelerates Cr deposition process, resulting in a wider deposition area of 5.9μm on LSM surface. The present results show that the Cr deposition occurs beyond the electrolyte/electrode interface, which reveals that the deposition of Cr species is driven by chemical reaction, not electrochemical reduction. Cr species are induced to deposit on LSM cathode surface by chemical reaction with Mn2+ ions, and extend to YSZ surface under cathodic current.

Modified Butler-Volmer Type Model Which Accounts for Triple and Double Phase Boundary Reaction Pathways

Modeling electrochemical reactions in solid oxide fuel cells (SOFCs) is a difficult and contentious topic. Recently, detailed reduced order reaction models have been presented which take into account more detailed physics than the widely used Butler-Volmer (BV) type equations. For this study, a reduced order oxygen reduction reaction (ORR) model previously developed specifically for yttria stabilized zirconia (YSZ)/lanthanum strontium manganite (LSM) cathodes is considered. The most prominent electrochemical pathways have been identified as the triple phase boundary (YSZ/LSM/pore) or surface pathway and the double phase boundary (YSZ/LSM) or bulk pathway. The ORR model considered predicts a competition between which pathway is most prominent depending on local overpotential, reactions rates and species concentrations (particularly oxygen partial pressure). However, this model and those similar to it require separate species transport equations to be solved for numerous species and surface coverages which result in a very stiff system of non-linear equations. Such a system becomes cumbersome numerically especially when trying to perform complex simulations such as impedance analyses, in comparison to BV type models. On the other hand, the traditional BV type equations are not able to distinguish between the reactions at the triple phase boundaries (TPBs) and the double phase boundaries (DPBs). In the study, the relationships between the total current, over potential, oxygen partial pressure, temperature and particularly TPB and DPB are explored based on the previously developed ORR model and experimental data from literature. Using these relationships, a new model is proposed for calculating the exchange current density as part of a BV type model which takes into account both TPB and DPB pathways as well as oxygen partial pressure. The model is then applied to situations of different TPB and DPB densities and reaction rates (exchange current densities) and compared to similar studies using the ORR model in order to verify that the model correctly handles the relationship between the two current pathways. It was found that the proposed BV model produces results comparable to the ORR model all with computational time for similar analyses being approximately 10,000 times shorter (due to decreased stiffness). The results obtained from the BV model are encouraging and indicate that a similar model can be developed for the anode side and different cathode materials, thus resulting in a robust modeling and analysis tool for SOFCs. This would amount to huge time and cost savings especially for simulations of large planar cells and cell stacks.

Double Layered CeO2-Co3O4-CuO Based Anode for Direct Utilisation of Methane or Ethanol in SOFC

Solid oxide fuel cells have been subject of many developments especially concerning alternative fuels such as hydrocarbons and alcohols, mainly because these devices can convert chemical potential into electricity with high efficiencies. In addition, the direct utilisation of hydrocarbons or alcohols as fuels increases the feasibility of SOFC market penetration. However, issues such as coking and clogging by carbon formation must be overcome before the technology can be safely delivered to final consumers. Therefore, the aim of this work was to develop an anode material capable of using methane or ethanol as fuels directly into the cell without any pre-reforming which could prevent carbon to deactivate the anode material. A bimetallic Ceria-based electrocatalyst was thus prepared using Cobalt and Copper oxides to enhance catalytic activity and electrical conductivity. Two different compositions were produced, a Cerium-rich composition with the molar proportion of Ce:Co:Cu – 2:1:1 and a Cobalt-rich one, Ce:Co:Cu – 1:2:1. The electrocatalyst powder was synthesised by the amorphous citrate method and characterised by X-Ray diffraction (XRD), Rietveld refinement, and temperature-programmed reduction (TPR). The powders produced were pelletised, sintered, and then submitted to Van der Pauw 4-probe DC conductivity tests. ScCeSZr electrolyte-supported cells were produced with a Lanthanum Strontium-doped manganite cathode screen printed onto the electrolyte. The anode was comprised with a double layer of the aforesaid compositions and a Sc10Ce1Zr + CeO2 inner layer that provided more stability between the electrolyte and the anode. The cell was tested under hydrogen as fuel and oxygen as oxidant from 750 to 850 ˚C, and then with anhydrous methane and ethanol separately as fuels at 850 ˚C. After operation, the cell was submitted to Raman spectroscopy to assess any evidence of carbon deposition through the anode microstructure. Moreover, scanning electron microscopy was conducted to evaluate the anode morphology and conditions concerning its microstructure. XRD spectra showed that the desired bimetallic CeO2-Co3O4-CuO oxide was formed and Rietveld refinement indicated that the formation of solid solutions did not occur. TPR demonstrated the ability of both compositions to absorb hydrogen by reducing its oxides as expected. DC conductivity tests presented suitable values since the tests were taken over the oxidised sample. The cell could operate in hydrogen, methane or ethanol as fuels showing maximum power densities of approximately 400, 100 and 160 mW.cm–2, respectively, at 850 ˚C. Raman spectroscopy was performed over several spots on the cell during post-mortem analysis and no evidence of carbon deposition was found on the anode. SEM images showed a homogenous microstructure concerning surface morphology and pore distribution. Finally, it was found that the bimetallic electrocatalyst anode could utilise hydrocarbon fuels directly without pre-reforming and produce a reasonable power density with no evidence of carbon coking which shows that this material configuration is promising as anode for carbonaceous fuels.

Modified Butler-Volmer Type Model Which Accounts for Triple and Double Phase Boundary Reaction Pathways

In recent years, detailed reduced order reaction models have been presented which consider more detailed physics than the widely-used Butler-Volmer (BV) equations. A reduced order oxygen reduction reaction (ORR) model previously developed specifically for yttria stabilized zirconia (YSZ)/lanthanum strontium manganite (LSM) cathodes is studied here. This model requires separate species transport equations to be solved for numerous species and surface coverages resulting in a stiff system of non-linear equations. However, models that apply the traditional BV type equations, while much less computationally intensive, are not able to distinguish between the reactions at the triple phase boundaries (TPBs) and the double phase boundaries (DPBs). In the study, the relationship between over potential and current density at TPBs and DPBs is explored based on the aforementioned ORR model and a new BV type model is proposed for modeling the exchange current density considering both TPB and DPB pathways.

Optimization of spin-coated electrodes for electrolyte-supported solid oxide fuel cells

Electrodes for electrolyte-supported solid oxide fuel cells (SOFC's) were fabricated by spin coating. Strontium- doped lanthanum manganite (LSM) cathode and nickel yttria-stabilized zirconia cermet anodes were synthesized and processed for enhanced deposition conditions. The influence of electrode microstructural parameters was investigated by a systematic experimental procedure aiming at optimized electrochemical performance of single cells. Polarization curves showed a strong dependence on both electrode thickness and sintering temperature. By a systematic control of such parameters, the performance of single cells was significantly enhanced due to decreasing of polarization resistance from 26 I© cm² to 0.6 I© cm² at 800°C. The results showed that spin-coated electrodes can be optimized for fast and cost effective fabrication of SOFCs.

Understanding the electrochemical behaviour of LSM-based SOFC cathodes. Part II - Mechanistic modelling and physically-based interpretation

This study presents a physically-based model for the impedance simulation of the oxygen reduction reaction in porous strontium-doped lanthanum manganite (LSM) cathodes. The model describes the surface mechanism only, taking into account the co-limited adsorption/diffusion of oxygen and the charge-transfer reaction at the three-phase boundary (TPB). After calibration with experimental impedance spectra, the model is used to identify the transition of kinetic regime from the surface to the bulk path mechanism, which occurs at cathodic dc bias of ca. 0.2V within 700–800°C. The transition is highlighted by a significant decrease in impedance and the appearance of a low-frequency inductive loop. The model consistently reproduces the impedance spectra before the transition of kinetic regime with a single set of parameters, allowing for the deconvolution of two features, one associated with the co-limited adsorption/diffusion process (ca. 5Hz) and another minor contribution due to the charge-transfer at the TPB (ca. 35Hz). The model and its parameters, which quantitatively agree with the literature, can be used as a basis to optimize the microstructural and surface properties of technical LSM-based cathodes, showing that the TPB length is not the main parameter to be maximized.

Effect of A site deficiency of LSM cathode on the electrochemical performance of SOFCs with stabilized zirconia electrolyte

The effect of A site deficiency on the electrochemical performance of a strontium-doped lanthanum manganite (LSM) cathode in an ScSZ electrolyte-supported solid oxide fuel cell (SOFC) was investigated. XRD characterization resulted in a series of (La0.75Sr0.25)xMnO3 (x=1.0, 0.97, 0.95, 0.9 and 0.85) powders, indicating that the Mn3O4 phase precipitated into (LS)xM when the deficiency value was over a certain threshold value. The chemical reaction occurred between stoichiometric LSM and ScSZ due to the high chemical potential of La. An A site deficiency in the LSM can reduce the chemical potential of La and suppress the interfacial reaction between the LSM and ScSZ. The precipitation of Mn3O4 due to a larger A site deficiency leads to the formation of LZO occurring at the A site-deficient (LS)xM and ScSZ. An A site-deficient (LS)xM cathode appears to possess good adhesion with the ScSZ electrolyte and a longer active TPB length after being sintered at 1300°C. An optimal A site deficiency concentration was considered to exist in the electrochemical performance improvement of the A site-deficient LSM cathode SOFC.