Strontium-doped Lanthanum Manganite Research Articles

EFFECT OF SR CONTENT ON THE MICROSTRUCTURE DEVELOPMENT AND ELECTROCHEMICAL PERFORMANCE OF LA1-XSRXMNO3 FILMS

Strontium doped lanthanum manganite (La1-xSrxMnO3 -LSM) is the conventionally used oxygen reduction electrocatalyst in solid oxide fuel cell cathodes. In recent years, Sr-segregation at the LSM surface has been shown to occur and limit oxygen reduction performance. Therefore, the effect of Sr-doping on the microstructure development and performance of liquid precursor-derived LSM film electrodes with different Sr-contents was investigated in this study. It was found that as Sr content increased, LSM structure became amorphous, which is beneficial for the electrochemical performance. Despite this fact, the undoped LaMnO3 film performed better in comparison to heavily Sr-doped LSM, likely because of Sr-segregation at the Sr-doped electrode surface. These results suggested that trying to avoid Sr doping in LaMnO3 electrodes may be a good strategy if its microstructural instability could be addressed, to achieve high performance solid oxide fuel cell cathodes.

Formulation of an Ideal Solid Oxide Fuel Cell

Principles of transport phenomena and chemical/ electrochemical reaction kinetics were employed to develop the formulation for the prediction of fuel (e.g., ) and oxidant (e.g., ) mole fraction profiles in the porous anode and cathode electrodes of an ideal solid oxide fuel cell (SOFC). The ideal SOFC is composed of the porous anode, , which is the cermet of metallic nickel and yttria-stabilized zirconia and the porous cathode, , which is the strontium-doped lanthanum manganite. A thin film of the yttria-stabilized zirconia is the solid electrolyte separating the cell electrodes. The cell anode-side fuel and cathode-side oxidant supply compartments are continuously stirred to maintain constant concentrations of fuel and oxidant in them. The relevant analytical formulation as well as the numerical data computed is presented. The current calculated data show a non-linear decrease, associated with the coupled effect of diffusion and consumption, in the mole fractions of hydrogen and oxygen in the porous electrodes with an increase in the distance from the reactant supply compartments towards the cell electrolyte separator.

Multicomponent Mixed Ionic and Electronic Conducting (MIEC) Air Electrodes and Their Heterointerface for Effective Application in Reversible Solid Oxide Cell (R-SOC): Efficacy of Stoichiometric and Off-Stoichiometric Compositions

Reversible solid oxide cell (R-SOC) has triggered research interest from the past few years for its reversible applicability for power-to-fuel (P2F) in electrolyser cell (SOEC) to generate hydrogen by splitting of high temperature steam and fuel-to-power (F2P) in fuel cell (SOFC) mode of operation to produce power by oxidation of fuel with >80% conversion efficiency [1]. Primarily, R-SOC consists of a dense electrolyte conventionally yttria stabilized zirconia (YSZ), bridged between two porous electrodes, e.g., strontium doped lanthanum manganite (LSM) as air electrode and Nickel (Ni)-YSZ cermet as fuel electrode. Significant research has been devoted to carry out the long-term stability (≥ 2000 h) degradation in endurance test primarily due to major challenges like highly humid environment in the fuel electrode, microstructural flaws and polarization losses under high operational temperature. In this context, mixed ionic and electronically conducting (MIEC) oxide-based La-Sr-Co-Fe-O (LSCF) and Ba-Sr-Co-Fe-O (BSCF) air electrodes has drawn significant attention for the effective oxygen reduction (ORR) and oxygen evolution (OER) reaction in the context of SOFC and SOEC operational mode [2,3].An attempt has been made in this present research work to establish the effect of off-stoichiometry in A-site lattice over the stoichiometric pristine compositions of La/Ba-Sr-Co-Fe-O (LSCF/BSCF)-based multicomponent MIEC-oxides and their associated heterostructure with optimised off-stoichiometric compositions that governs the electrochemical redox phenomena in conjunction with the functionally engineered Gd-doped ceria-based interlayer and buffer layer. Vacancy driven oxygen reduction (ORR) and oxide ion oxidation (OER) kinetics as a function of aliovalent charge compensation mechanism associated with the defect chemistry has also been investigated for these A-site non-stoichiometric compositions in the range of 1-0.92 for La/Ba(1-x)SrxCo1-yFeyO3-δ [x=0.4 and y=0.2]. A comparative study between the performance of the off-stoichiometric heterostructure synthesised using the optimised pristine compositions with that of the stoichiometric heterointerface has also been evaluated for their efficiency as catalyst for OER/ORR in reversible SOC mode of operation. The increasing trend of oxygen non-stoichiometry (δ) upon the transition from A-site stoichiometry to non-stoichiometric compositions reflected the formation of higher aliovalent cation of ‘Co’ to maintain the charge neutrality and thereby accelerates the associated oxygen redox kinetics. An optimum δ-value of 0.33 and 0.37 are found for LSCF and BSCF-compositions respectively having A-site non-stoichiometry of 0.94. Current density of 0.45 A.cm-2 at an applied voltage of 1.5 V @800℃ is obtained for stoichiometric composition of LSCF wherein 0.5 A.cm-2 is found for the off-stoichiometric batch corresponding to the hydrogen flux of 0.21Nl.h-1.cm-2. Such augmentation in performance may be related to the formation of higher lattice defect which eases the path for oxide ion oxidation. Formation of the interpenetrating heterointerface network at the air electrodes and electrode/electrolyte interfaces in the morphologically engineered cells having gradation in porosity has further been confirmed from Transmission Electron Microscopy (TEM) studies involving the high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and the STEM-EDS elemental spectrum mapping images of the cross-section of the sintered cells and clinically corelated with SOC performances. Orientation of the crystal lattice planes in the two types of grains across the heterojunction has also been determined from the High-Resolution Transmission Electron Microscopy (HRTEM) images. Further study to envisage the presumed hypothesis, based on the rate determining steps involving the defect lattice formation and probable mechanism for selective ORR/OER application, will also be described through hole and/or oxygen vacancy formalism using XPS and density functional theory (DFT) for such hetero-interpenetrating air electrodes.

Electrochemical performance and stability of PrO1.833 as an oxygen electrode for solid oxide electrolysis cells

Significant efforts have recently been undertaken to develop highly efficient solid oxide cells for high-temperature steam electrolysis (SOEC). Implementing new materials and microstructures that would improve the performance and durability of this technology remains a major issue. For this purpose, a nano-structured PrO1.833 material coated by the electrostatic spray deposition (ESD) technique was studied as a promising active oxygen electrode for SOEC application. The study was performed considering the PrOx as the functional layer and strontium-doped lanthanum manganite (LSM) as the current collecting layer on a standard half-cell supported by a typical Ni-YSZ cermet, a YSZ electrolyte, and a gadolinium-doped ceria (GDC) barrier layer. The electrochemical characterizations showed promising initial performance at 700 °C in SOEC mode (− 1 A cm−2 at 1.4 V with H2O/H2 = 90 vol%/10 vol%). In addition, a reasonable degradation rate of ∼5.8% kh−1 was obtained at 700 °C within 1000 h of SOEC operation. The structural and elemental evolutions were analyzed with micrometer size resolution all along the functional layer thickness using synchrotron μ-X-ray diffraction and fluorescence. The electrode degradation was primarily attributed to the phase transitions of PrO1.833. In particular, the structural analyses of the sample aged under applied current revealed a small quantity of PrO1.5≤x≤1.7 phase at the GDC/AFL (active functional layer) interface which is expected to be less conductive than PrO1.833, along with PrO1.714 and GDC phases. Finally, additional structural characterizations were performed on samples annealed at different temperatures and dwell times: 700 °C for 1000 h and 800 °C for 700 h, respectively. The results are discussed to provide a better understanding of the stability of the praseodymium oxide.

Consistency between theoretical conduction models and experimental conductivity measurements of strontium-doped lanthanum manganite

La0.9Sr0.1MnO3 nanoparticles are elaborated using the citrate-gel route. The X-ray patterns show that the prepared sample crystallizes in the rhombohedral symmetry. Interesting results were obtained from the electrical conductivity measurements of the lanthanum manganite doped low strontium content. Indeed, numerous conduction models are used to analyze the electrical conductivity response. It is found that transport properties are governed by hopping processes at different temperature ranges. Such mechanisms explain the evolution of the DC-conductivity as well as the displacement of charge-carriers with temperature excitation. Then, thermal activation of the charge-carriers is confirmed. The temperature dependence of the frequency exponents reveals the contribution of Non-overlapping Small Polaron Tunneling (NSPT), Quantum Mechanical Tunneling (QMT), Over-lapping Large Polaron Tunneling (OLPT) and Correlated Barrier Hopping (CBH) to the transport properties. Conductivity spectrum shows a significant increase with frequency in the temperature range [80–500 K]. The frequency dependence of the AC-conductivity obeys to the "Double Jonscher Power Law" in the temperature range [80–300 K]. From 340 to 500 K, it is governed by the "Single Jonscher Power Law". Moreover, a high frequency plateau is observed presenting a percolation behavior in the conductivity spectrum. The deduced values of the disorder and hopping energies show the impact of hopping distance and polaron radius on the charge-carriers transport.

Tuning between composition and nanoparticle size of manganites for self-regulated magnetic hyperthermia applications

Self-regulated magnetic hyperthermia is a promising alternative for cancer treatment based on tumor annihilation by heating using appropriate Curie temperature () as an internal temperature controller. We successfully prepared strontium-doped lanthanum manganite nanoparticles (LSMO-x) using the sol-gel method. The can be adjusted by modifying both the composition and diameter of the particles, that is, varying the Sr content (0.2 0.3) and the annealing temperature (600 ∘C, 700 ∘C, and 800 ∘C). Structural, morphological, chemical, and magnetic properties were investigated. The samples exhibit the structure of perovskites with average particle sizes ranging from 17 nm to 27 nm, depending on the annealing temperature. This diameter range ensures that all samples investigated are have negligible remanence at room temperature. Magnetization studies show that increases as Sr content and particle size increase, indicating that the is governed by both. Thus can be adjusted by combining these two parameters for self-regulated magnetic hyperthermia. Magnetic hyperthermia measurements showed that samples with larger particle sizes (19 nm) were more efficient in promoting heat, that is, presenting a higher specific absorption rate (SAR), probably due to the adequate balance between the Néel and Brownian relaxations behavior. We figure out that the SAR value is essential for this specific finality, but it should also consider the maximum temperature reached during the hyperthermia essays. Finally, we build up a nanoparticle diameter vs. Sr concentration phase diagram, where the SAR values are displayed, which allows for predicting the best sample for the self-regulated hyperthermia.

(Invited) Chemical Stability and Performance of Rare Earth Nickelate Oxygen Electrodes for Reversible Solid Oxide Cells

Composite rare-earth nickelate-rare-earth doped ceria oxygen electrodes have inherent chemical instabilities. Over the last year, we have made progress on achieving chemical stability and high performance using a strategy of heavily doping the ceria phase with rare-earth cations. A higher dopant concentration of a rare-earth cation in the ceria phase ensures thermodynamic stability of the nickelate phase in contact with the ceria phase. In particular, composite oxygen electrodes comprising lanthanum nickelate La2NiO4+δ (LNO) - lanthanum doped ceria (LDC) and neodymium nickelate Nd2NiO4+δ (NNO) - neodymium doped ceria (NDC) have been electrochemically tested in both solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes. The performance of these cells have been compared to a composite strontium doped lanthanum manganite (LSM)-8 mol% yttria stabilized zirconia (YSZ) electrode. Both nickelate based electrodes achieve far superior performance compared to the LSM electrodes. We also report impedance measurements from symmetrical cells featuring LNO and NNO electrodes, analyzed using a distribution of relaxation times (DRT) approach. The DRT analysis reveals significant differences in the rate controlling steps in oxygen reduction and incorporation steps between the two materials. Lastly, oxygen surface exchange results for LNO and NNO are also reported which show different oxygen exchange kinetics when measured on dense versus porous materials which have implications for deploying these materials in reversible solid oxide cells.

The effect of synthesis method on oxygen nonstoichiometry and electrical conductivity of Sr-doped lanthanum manganites

The strontium-doped lanthanum manganites (La1-xSrxMnO3, LSMO) have potential use in devices for energy conversion and storage due to their chemical stability and high electrical conductivity. In this study, LSMO (x = 0, 0.1, 0.2, 0.3) were prepared by the citrate-nitrate autocombustion (CNA) and coprecipitation synthesis. The formation of the LSMO phase was confirmed by X-ray diffraction and the lattice parameters were determined by Rietveld refinement analysis. The oxygen nonstoichiometry in samples was determined by permanganate titration. The results of electrical conductivity measurement have shown semiconductor behaviuor in all samples, with conductivity rising with temperature and Sr-amount. Furthermore, it was observed that LSMO samples prepared by the coprecipitation method possess higher conductivity than samples prepared with the CNA method due to the higher oxygen nonstoichiometry. Electrical conductivities of all LSMO samples were in 10−2–0.45 Ω−1 cm−1 range, which is comparable to the conductivity of Si.

Microwave sintering study of strontium-doped lanthanum manganite in a single-mode microwave with electric and magnetic field at 2.45 GHz

The objective of this work is to study the changes in the physical and mechanical properties of strontium-doped lanthanum manganite (LSM) material and LSM-YSZ (ZrO2 doped with 8 mol% yttria) composite, obtained by colloidal processing and sintered by 2.45 GHz microwave sintering at 1200 and 1300 °C using two different single-mode cavities. One circular cavity with TE111 mode that has maximum in the electric field (E-field) and one rectangular cavity with TE102 mode that has maximum in the magnetic field (H-field). As compared to conventional sintering at 1300 and 1400 °C, the microwave-heated samples exhibited a denser structure for shorter sintering times. LSM-based materials showed higher heating behavior in H-field, which translates into higher energy absorption. This fact can be attributed to an electromagnetic pressure induced by the combined effect of current loops subjected to H-field. Therefore, the interaction between the material and the electromagnetic waves depends on the dominant field of them.

Smart Bone Graft Composite for Cancer Therapy Using Magnetic Hyperthermia

Magnetic hyperthermia (MHT) is a therapy that uses the heat generated by a magnetic material for cancer treatment. Magnetite nanoparticles are the most used materials in MHT. However, magnetite has a high Curie temperature (Tc~580 °C), and its use may generate local superheating. To overcome this problem, strontium-doped lanthanum manganite could replace magnetite because it shows a Tc near the ideal range (42–45 °C). In this study, we developed a smart composite formed by an F18 bioactive glass matrix with different amounts of Lanthanum-Strontium Manganite (LSM) powder (5, 10, 20, and 30 wt.% LSM). The effect of LSM addition was analyzed in terms of sinterability, magnetic properties, heating ability under a magnetic field, and in vitro bioactivity. The saturation magnetization (Ms) and remanent magnetization (Mr) increased by the LSM content, the confinement of LSM particles within the bioactive glass matrix also caused an increase in Tc. Calorimetry evaluation revealed a temperature increase from 5 °C (composition LSM5) to 15 °C (LSM30). The specific absorption rates were also calculated. Bioactivity measurements demonstrated HCA formation on the surface of all the composites in up to 15 days. The best material reached 40 °C, demonstrating the proof of concept sought in this research. Therefore, these composites have great potential for bone cancer therapy and should be further explored.

Simultaneous oxidation of aromatic compounds using Sr‐doped lanthanum manganites as catalysts

Strontium-doped lanthanum manganites, La1-xSrxMnO3 (LSMO), are promising and affordable catalysts for oxidative degradation of volatile organic compounds. LSMO catalysts (x = 0, .1, .2, and .3) were prepared by the citrate-nitrate autocombustion (CNA) and coprecipitation synthesis. The phase composition was confirmed by X-ray diffraction and Rietveld refinement analysis, while the oxygen content was determined by Mohr's salt permanganate titration. Morphology and porosity of prepared catalysts was correlated to catalytic oxidation of benzene, toluene, ethylbenzene and o-xylene. It was observed that both synthesis methods yielded catalysts of similar average pore size diameter and specific surface area, but the pore size distribution differed: CNA-prepared catalysts had a multimodal pore size distribution, while the coprecipitated ones had a single maximum at 4 nm. Catalysts prepared by the CNA method have shown a higher catalytic activity in the temperature range 373–723 K, as the presence of Mn3+/Mn4+ mixed valences increased their reducibility.

A Study of the Electrochemical Characteristics of Single-Chamber Solid Oxide Fuel Cells Based on Platinum and Strontium-Doped Lanthanum Manganite Electrodes and Fed with a Methane–Air Mixture

A Study of the Electrochemical Characteristics of Single-Chamber Solid Oxide Fuel Cells Based on Platinum and Strontium-Doped Lanthanum Manganite Electrodes and Fed with a Methane–Air Mixture

Enhanced Catalytic Performance of Strontium-Doped Lanthanum Manganites by the Presence of Molybdenum Oxides for Electro-Reduction of Hydrogen Peroxide

In this work, two catalysts, lanthanum manganite strontium-doped perovskite without (LSM) and with (LSMMO) mixed molybdenum oxides, were synthesized by the sol-gel route and deposited by immersion in carbon cloth substrates. Their performance as cathodes in the hydrogen peroxide reduction reaction (HPRR) and oxygen reduction reaction (ORR) was investigated through cyclic voltammetry and electrochemical impedance spectroscopy, the electrocatalytic efficiency of these electrodes in the HPRR was analyzed in KOH and H2O2 medium at 298 K. The performance of the cathodes, in a single compartment, using a nickel plate as an anode was also investigated. The results showed that for the reduction reactions, electrodes developed with LSMMO have more significant catalytic activity than LSM after polarization, resulting in 32% higher current densities, lower electrical resistance after polarization, and a 21% increase in power density.

Investigating the effect of nano-structured magnetic particles lanthanum strontium manganite on perovskite solar cells

In this study, pure phase nanostructured strontium-doped lanthanum manganite, La0.75Sr0.25MnO3 (LSM), with a hexagonal structure was synthesized by sonochemical method. Then, XRD and SEM estimated the size of the LSM nanopowders. The results are exhibited that products synthesized in this method are compatible with particle size and morphology. Magnetic measurement was done by vibrating sample measurement (VSM) on LSM nanoparticles at room temperature. According to the results obtained from VSM displayed the saturation magnetization of LSM nanoparticles exhibited a maximum of 24.25 emu/g at room temperature. Then, the influence of LSM nanoparticle as an additive on the film morphology of CH3NH3PbI3 and the performance of perovskite solar cells was examined. We explore by using 5wt % of additive can increase the short current density (Jsc) from 14.45±0.55 to 18.29±0.38 mA/cm2 (~ 26.5 % enhancement) and power-conversion efficiency (PCE) from 8.33±0.40 to 12.41±0.35 (~ 49 % enhancement). Moreover, the morphology, and band gap of the new perovskite layer was improved.

Stable High Performance Rare-Earth Nickelate Based Oxygen Electrodes for Reversible Solid Oxide Fuel Cells and Electrolyzers

The performance of composite rare-earth nickelate-rare-earth doped ceria composite oxygen electrodes, with a high concentration of rare-earth doping in ceria to stabilize the nickelate phases are reported. Additionally, the stability of these compositions is reported at both the sintering (1240°C) and operating temperatures (800°C). Specifically, a lanthanum nickelate La2NiO4+δ (LNO) -45 mol% lanthanum doped ceria (LDC45) oxygen electrode has been tested in both solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes. The performance of this cell has been compared with a composite oxygen electrode comprising 20 mol% strontium doped lanthanum manganite (LSM)-10 mol% scandia 1 mol% ceria stabilized zirconia (SSZ) electrode. The LNO–LDC45 composite oxygen electrode shows a 65% increase in current density at 0.8 V, and a 260% increase in current density at 1.2 V compared to LSM-SSZ oxygen electrodes in SOFC and SOEC mode respectively. Additionally, long term performance data shows that this superior performance can be maintained for long operating times at 1.2 V in SOEC mode at 800°C. Supplemental cell tests also show comparable performance for a composite neodymium nickelate Nd2NiO4+δ (NNO)- 50 mol% neodymium doped ceria (NDC50) and a composite LNO- 50 mol% lanthanum doped ceria (LDC50) electrode.

Micro-Tubular Solid Oxide Fuel Cells with One Closed-End Fabricated Via Dip-Coating and Co-Firing

Tubular solid oxide fuel cells (SOFCs) with one closed-end configuration have high tolerance of thermal cycling owing to the capability of expanding and shrinking freely in response to thermal stresses. Additionally, tubular cells with one closed-end have simple sealing requirements, and enable making the stacks with uniform temperature distribution. In this study, anode supported micro-tubular SOFCs with one closed-end were manufactured successfully by dip-coating and co-firing methods using carbon rods with round end as a template. A dense electrolyte layer was obtained at a co-firing temperature of 1400 °C, followed by cathode deposition and sintering. The prepared micro-tubular SOFCs comprised of Ni-yttria-stabilized zirconia (YSZ), Ni–scandia-stabilized zirconia (SSZ), strontium-doped lanthanum manganite (LSM)-SSZ, and LSM as the anode support, anode functional layer, electrolyte, cathode functional layer, and cathode current collector, respectively. The electrochemical performance and microstructure of fabricated closed-end micro-tubular SOFC was evaluated by electrochemical characterization and scanning electron microscopy. The developed dip-coating method is fast in turnaround time and enables fabricating the one closed-end tubes of various lengths and diameters by co-firing.

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.

Micro-Tubular Solid Oxide Fuel Cells with One Closed-End Fabricated Via Dip-Coating and Co-Firing

The tubular solid oxide fuel cells (SOFCs) with one closed-end configuration have high thermal-cycling tolerance owing to the capability of expanding and shrinking freely in response to thermal stresses. The tubular cells with one closed-end have simple sealing requirements, and enable making the stacks with uniform temperature distribution. In this study, anode supported micro-tubular SOFCs with one closed-end were manufactured successfully by dip-coating and co-firing methods using carbon rods as a template. A dense electrolyte layer was obtained at a co-firing temperature of 1400°C, followed by cathode deposition and sintering. The prepared micro-tubular SOFCs were comprised of Ni-yttria-stabilized zirconia, Ni–scandia-stabilized zirconia (SSZ), SSZ, strontium-doped lanthanum manganite (LSM)-SSZ, and LSM as the anode support, anode functional layer, electrolyte, cathode functional layer, and cathode current collector, respectively. The developed dip-coating method is fast in turnaround time and enables fabricating the one closed-end tubes of various lengths and diameters by co-firing.

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.

Permanganometric determination of oxygen nonstoichiometry in manganites

Strontium and lanthanum manganites are nowadays the subject of extensive research because of their promising electrical and magnetic properties. Strontium manganite, SrMnO3, was successfully prepared by citrate-nitrate autocombustion (CNA) and by the coprecipitation method. These methods were then applied to synthesis of strontium doped lanthanum manganites, La1-xSrxMnO3 (x ​= ​0, 0.1, 0.2 and 0.3). The optimal phase formation conditions were determined by thermogravimetry and differential scanning calorimetry. Crystallization of precursors and calcined powders was studied by X-ray diffraction. Powders, in which pure manganite phase was obtained, were also analyzed by permanganate titration with Mohr’s salt in order to determine oxygen nonstoichiometry. Oxygen stoichiometry was achieved in SrMnO3 powders obtained by the CNA method and calcined at 1000 ​°C as well as in powders obtained by the coprecipitation method and calcined at 1200 ​°C. La1-xSrxMnO3 phase was oxygen stoichiometric for x ​= ​0.3 while decreasing of x resulted in cation deficiency, i.e. oxygen excess. Oxygen deficit was achieved for x ​= ​0.09 upon calcination at 1200 ​°C. The obtained results were confirmed by thermogravimetry and the Rietveld refinement analysis.