Search

The matrix material in a Molten Carbonate Fuel Cell, usually LiAlO2, has an important role in the ionic conduction, gas sealing and electrolyte retention. To avoid cracking, this material has been reinforced with various additives, mostly Al-based, which are subject to in situ lithiation. In this work, matrices were systematically synthesized through a fast and more environmentally friendly route and characterized, with two types of reinforcing agent, either Al powder or Al2O3 fibers, both with and without carbonates. Then, a comparative analysis was done, in terms of mechanical strength and porosity, on the effect of adding Al powder and Al2O3 fibers and their subsequent lithiation. This reaction was found to be quantitative after 50 h at 650 °C, and matrices with reinforcing agent and carbonates featured increased mechanical strength by a factor up to 2 compared to matrices with only reinforcing agent, reaching 0.61 kgf.mm−2. Al powder was also found to be better suited than Al2O3 fibers for addition in a matrix, also contributing to enhance the porosity, particularly after lithiation.

The increase in longevity worldwide has intensified the use of different types of prostheses for the human body, such as those used in dental work as well as in hip and knee replacements. Currently, Ti-6Al-4V is widely used as a joint implant due to its good mechanical properties and durability. However, studies have revealed that this alloy can release metal ions or particles harmful to human health. The mechanisms are not well understood yet and may involve wear and/or corrosion. Therefore, in this work, commercial pure titanium and a Ti-6Al-4V alloy were investigated before and after being exposed to a simulated biological fluid through tribological tests, surface analysis, and ionic dissolution characterization by ICP-AES. Before exposure, X-ray diffraction and optical microscopy revealed equiaxed α-Ti in both materials and β-Ti in Ti-6Al-4V. Scratch tests exhibited a lower coefficient of friction for Ti-6Al-4V alloy than commercially pure titanium. After exposure, X-ray photoelectron spectroscopy and surface-enhanced Raman spectroscopy results showed an oxide film formed by TiO2, both in commercially pure titanium and in Ti-6Al-4V, and by TiO and Al2O3 associated with the presence of the alloys. Furthermore, inductively coupled plasma atomic emission spectroscopy revealed that aluminum was the main ion released for Ti-6Al-4V, giving negligible values for the other metal ions.

In this work, PdFe2O3 bimetallic materials containing oxygen vacancies (Ov, from 10 to 75%) and two bimetallic nanoparticles based on noble metals (PdAu and PdPt) were obtained and evaluated for the ethanol electro‒oxidation reaction (EOR) in alkaline medium. For this purpose, bimetallic nanoparticles were synthesized keeping similar crystallite sizes (~6 nm), particle sizes (~6 nm), mass compositions (18 ± 4% co‒metal) and metallic loadings (18.3 ± 5.1%). PdAu/C, PdPt/C and the most active PdFe2O3/C material (75% of Ov) displayed an improved onset potential (Eonset) during the oxidation of 1.5 M ethanol in 0.3 M KOH in comparison with a monometallic Pd/C material, finding the trend: PdAu/C (−0.56 V vs. NHE) > PdPt/C (−0.55 V) > PdFe2O3/C (−0.51 V) > Pd/C (−0.50 V). In addition, these bimetallic materials presented an increase in the current density; being PdPt/C and PdFe2O3/C the most active materials for EOR. A spectroelectrochemical analysis was performed by coupling a μRaman spectroscope with an electrochemical cell. This analysis allowed to conclude that the improvement of the Eonset is related to changes in chemisorption energies as was suggested by Raman shifts found for the C1‒M (metal) bond, while the high activity of PdPt/C can be attributed to a higher adsorption of ethanol molecules. Additionally, it was found that the activity of PdFe2O3/C is associated with an energy decrease to form the C1‒M bond, which could be promoted by the abundance of oxygen vacancies.

Sorbitol is a potentially cheap fuel that can be easily produced from biomass. However, despite its renewable character, the sorbitol electro-oxidation reaction (SOR) has been barely studied, being mostly analyzed using massive or nanoparticulate Pt-based materials, exhibiting poor activity. This work proposes the green synthesis of Au/C, Pd/C and Au–Pd/C nanomaterials as alternative electrocatalysts to Pt, and evaluation of their activity for sorbitol electro-oxidation. These nanomaterials were synthesized using 2-hydroxy ethylammonium formate protic ionic liquid, and according to TEM micrographs, these materials presented particle sizes from 13 to 22 nm. The electrocatalytic evaluation of SOR at room temperature indicated that Pd/C had almost 3.5-fold higher current density than a commercial Pt/C. Au/C had similar activity than Pt/C, while Au–Pd/C presented 2-fold higher current density than Pt/C at a lower overpotential (60 mV). The activity for SOR of these materials was extended evaluating the electro-oxidation of the main sorbitol byproducts (glucose and gluconic acid). The resulting evaluation indicated that the excellent current density displayed by Pd/C for sorbitol oxidation can be related to a higher electron transfer per sorbitol molecule. In addition, the lowest overpotential presented by Au–Pd/C was associated with its ability to carry the dissociative adsorption of polyalcohols, which was confirmed using ethylene glycol as a simpler polyalcohol than sorbitol. The current density of Pd/C for sorbitol oxidation was 2-fold higher to that obtained for glucose and ethylene glycol, demonstrating the viability of using sorbitol as fuel for energy conversion applications.

International audience; Gadolinia doped ceria coatings were elaborated by cathodic arc evaporation from a metallic Ce–Gd (90–10 at.%) target inserted into a conventional multiarc Ti evaporation target in the presence of a reactive argon–oxygen gas mixture. The structural and chemical features of these films were determined by x-ray diffraction and scanning electron microscopy. Their electrical properties were characterized using impedance spectroscopy measurements. It was shown that the as-deposited coatings crystallize in the fluorite type fcc structure of ceria and that their composition is the same as that of the target. The morphology of the coatings is influenced by the evaporation parameter (stress and droplet). The electrical measurements showed two contributions in Nyquist representation and the activation energy was slightly higher than that given in the literature data for the bulk material.

In order to reduce carbon dioxide emission, one solution is to convert into valuable chemicals or fuels, e.g. transforming CO2 into CO by electrochemical reduction. Thus, this greenhouse gas could be re-used in particular as syngas (CO + H2) by co-electrolysis of CO2/H2O. High temperature electrolysis cells can be the best energetic devices to produce such syngas. In particular, molten carbonates are known to solubilize CO2 very significantly higher than other solvents. Therefore, it is compulsory to investigate and understand the mechanism of CO2 reduction in such media to consider its further use and valorisation. The present study is a critical approach aiming at elucidating the mechanisms for CO2 electroreduction, using an inert Pt electrode in the molten eutectic Li2CO3–K2CO3 (62-38 mol%), at 650 °C, under different partial pressures of CO2. Complementary electrochemical techniques, including sweep square-wave voltammetry and relaxation chronopotentiometry, were carried out. Their combination allowed us to evidence that the electroreduction of CO2 into CO is feasible in oxo-acidic conditions, involving a diffusion-limited quasi reversible system in a one electron-step.

CO2 plays a major role in the molten carbonate fuel cell (MCFC) and its reverse process, the molten carbonate electrolysis cell (MCEC), because of the capability of the mentioned electrolyte to capture big amounts of this greenhouse gas. In particular, the co-electrolysis process together with water, would ideally yield syngas (H2 + CO). The reduction of CO2 in such a case has been scarcely investigated in MCEC conditions. The present study is mainly focused on the online detection by Gas Chromatography (GC) of CO2 electrolysis product. Both thermodynamic predictions, including the chemical reactivity of CO and CH4, and experimental results on MCFC/MCEC performance and GC detection, allowed to prove that CO is produced electrochemically with a ratio depending on the electrolysis potential, deducing also the potentials that should be avoided to inhibit the formation of carbon. This first insight will be essential for analyzing the medium and long-term performance of MCECs.

Ti-6Al-4V alloy has been widely investigated for biomedical applications due to its low density, high specific strength, and favorable corrosion resistance. However, some reported failures have imposed a challenge to improve bone regeneration and fixation, as well as antibacterial properties. A further opportunity for solving this problem is the introduction of porosity. However, this can induce metallic release and corrosion product formation. In this work, a Ti-6Al-4V alloy was exposed to Hank’s solution, sterilized and inoculated with Staphylococcus aureus at 37 °C. Surface analysis was carried out by SEM-EDS and XPS. Electrochemical measurements were also performed using chronopotentiometry at open circuit potential, polarization curves, and electrochemical impedance spectroscopy. After exposure, FE-SEM showed some colonies of S. aureus on the sample with 22% porosity. However, XPS analysis revealed that the presence of bacterium influenced the composition of the oxide layer, even more drastically with the increase in added porosity. Moreover, the impedance analysis showed De Levie's behavior, revealing a reduction of pore resistance and modulus of the impedance in the low frequency range in inoculated medium, and polarization curves showed that the passivity potential range was decreased, whereas the passivity current increased in the presence of the S. aureus.

The accelerated degradation of a commercial LSCF/YDC/YSZ/Ni-YSZ solid oxide electrolyzer cell (La0.6Sr0.4Co0.2Fe0.8O3-δ/Y0.1CeO1.95/Y0.08Zr0.92O1.96/Ni-YSZ) contaminated by Si-containing impurities is studied with time under up to − 1.7 A cm−2 applied. Above ~ − 0.6 A cm−2, a new region appears in the polarization curve. This region corresponds to electronic conduction in the yttria-stabilized zirconia (YSZ) electrolyte, induced by the reduction under high current conditions. A shift in the typical frequencies (relaxation times) toward lower frequencies is then observed for the entire impedance spectra. This shift results finally in the disappearance of the positive loop related to the polarization resistance and the appearance of a negative (inductance type) loop which crosses the real axis (Z’) at the lowest frequencies to become positive again. This is characteristic for an electrode process mode in which the electrochemical redox reactions vanish while the cell current becomes mainly electronic due to the reduction of the YSZ electrolyte. This trend increases with time. Such a characterization of the electronic conduction of the YSZ electrolyte by electrochemical impedance spectroscopy has not been reported to date under electrolysis mode, to the best of our knowledge. Post-mortem analysis by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDX) shows detrimental degradation of the electrolyte after only 360 h of overall testing duration with numerous micropores in the YSZ volume, and cracks and delamination at the yttria-doped ceria (YDC)/YSZ interface. EDX analysis reveals (i) a migration of La, Sr, Co, and Fe elements from lanthanum strontium cobalt ferrite (LSCF) anode to YDC layer and YSZ electrolyte and (ii) a very important shift of Ni from Ni-YSZ cathode to YSZ and YDC, and also to LSCF anode in a lower proportion. This study highlights the critical issue that impurities represent for solid oxide electrolysis cell operation.

Degradation-related issues are among the main limitations to make solid oxide electrolysis cells (SOEC) meet performance targets economically viable for long-term operation. In this study, the considered cell presents a premature degradation during electrolysis operation observed after sealing the cell holder and the support pieces providing and releasing H2 electrode gas. This premature degradation is characterized by unusual polarization curve slopes, and appearance of a new impedance contribution at the lowest frequencies of the impedance diagrams recorded. To the best of our knowledge, this new contribution has never been reported for SOECs. Post-mortem analysis of the cell by scanning electron microscopy (SEM)/energy dispersive X-ray (EDX) shows the presence of Si, Al, Na, K, and Ca at the H2 electrode interface (surface and first dozens microns in the volume) and at the Ni-yttria-stabilized zirconia (YSZ)/YSZ interface, contrary to similar cells tested before sealing the pieces. This degradation is related to Si deposition, notably at the Ni/YSZ/H2O triple phase boundaries. Concomitantly, the new contribution observed, leading to a beneficial effect on the cell functioning, is assimilated to a “reactivation” contribution. This reactivation contribution is associated with an H2O adsorption phenomenon and characterized by a relaxation frequency of [1–10 mHz] and a capacitance of ~ 100 F cm−2. The evolution with time of the resistive and capacitive contributions is consistent with the interpretation of the premature cell degradation. A mechanism explaining the cell behavior after this premature degradation is proposed.

Adsorption of self-assembled monolayer (SAM) of different imidazolines derivatives was investigated on Fe2O3 (0 0 0 1) surface with DFT calculations to understand their corrosion inhibition mechanism. Quantum chemistry calculations enable us acquiring a better insight on the nature of imidazoline/surface interactions, i.e. partly covalent bonds, and self-organization of imidazoline ring on the surface than the previous force field-based studies. The SAM is composed of a network of H-bonded inhibitors. The influence of the alkyl chain length of imidazoline derivatives, which form a hydrophobic barrier above the surface, on the energetic and structural properties of the SAM was evaluated.

Co-electrolysis of water and carbon dioxide in molten carbonates is nowadays a key issue in MCEC (molten carbonate electrolysis cell) and, reversely, for a better understanding of MCFC (molten carbonate fuel cell). The products of water and carbon dioxide reduction are the fuels that might be used in MCFC or other energy devices. The present study is dedicated to a thorough electrochemical investigation by voltammetric techniques (Cyclic Voltammetry CV or Linear Sweep Voltammetry LSV) at a Pt electrode of such fuels in Li2CO3-K2CO3 eutectic, under varied atmosphere conditions, including partial pressures of H2O, CO2, H2 and Ar at 650°C. The conditions of formation of soluble and/or adsorbed H2 and CO are established together with qualitative thermodynamics information on the redox systems involved. C is only detected in very specific conditions. Knowing that hydroxides, produced in the conditions of MCEC and MCFC, have a significant role on the operation of such devices, an electrochemical analysis (CV and impedance measurements) of the effect of added amounts of hydroxides is developed for the first time, showing the enhancement of oxidation currents and the progressive increase in electrolyte conductivity.

In order to improve the electrochemical performances of the zinc-air cells, the material Nd1.98Sr0.02Ni0.99Co0.01O4 ± δ was prepared following the citrate method and used as cathode materials for alkaline room temperature fuel cells towards the oxygen reduction reaction (ORR). The microstructure and morphology before and after the ORR process were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical performances were followed by linear voltammetry and impedance spectroscopy. The results obtained are promising, the optical band gap is 1.36 eV showing that it is semiconductor and the voltammograms display two steps involving two electrons each. Moreover, the Nd1.98Sr0.02Ni0.99Co0.01O4 ± δ material allows obtaining higher current densities compared to black carbon and glassy carbon at different rotational speed. Impedance spectroscopy results confirm the good electrochemical performances of the analyzed material.

Room temperature ionic liquids (RTILs) attract much attention as a new type of environmentally benign electrolytes for Li-ion batteries due to their numerous interesting physicochemical properties. Here, in this paper, Li intercalation/deintercalation in presence of the N -butyl- N -methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (PYR 14 TFSI) and N -methyl- N -propylpyrrolidinium bis(fluorosulfonyl)imide (PYR 13 FSI) containing 0.3 M LiTFSI, was evaluated in a thin 100 nm layer of V 2 O 5 deposited on Al substrate by atomic layer deposition. Potentiodynamic tests performed in LiTFSI/Pyr 14 TFSI show a quasi-reversible Li intercalation during 10 cycles (between 2.4 and 5 V) with an average coulombic efficiency of 99%. The capacity, calculated from the 1st cycle, is found to be 182 mAh g −1 , about 19% (±2%) higher than the theoretical capacity reported for V 2 O 5 (147 mAh g −1 ). X-ray photoelectron spectroscopy analysis confirms that the intercalation of more than 1 mol of Li + per V 2 O 5 is achieved as also the possible presence of a solid permeable interface (SPI) layer on the V 2 O 5 surface. Likewise, the Li + in-depth distribution on the V 2 O 5 layer after intercalation in RTILs measured by time-of-flight secondary ion mass spectrometry ion depth profiles, show small irreversible electrode modifications with the presence of lithium through the entire V 2 O 5 layer with significant lithium trapping at the V 2 O 5 layer/Al substrate interface.

International audience; The present work proposes to explore how the presence of a periodic pattern at electrode/electrolyte interfaces of a SOFC could impact the electrochemical performances, from theoretical and experimental points of view. The model results demonstrate that a patterned interfaces along with an electrolyte having a thickness smaller than the dimensions of the pattern, lead to a strong increase of the exchange surface, hence to the exchange currents (up to 64%) with respect to flat interfaces. With the use of laboratory standard ceramic processes, this architecturation was experimented on YSZ-Ni self supported anodes on top of which a thin YSZ electrolyte was deposited. The first electrical tests for such a cell with a non-optimized thickness show an increase of the current density with respect to a cell with flat interfaces, from 130 to 300 mA cm-2 at 0.7 V, that is even higher than anticipated by the modeling.

Oxide–carbonate composite electrolytes are complex materials whose peculiar conductivity performances are yet to be fully understood. Stability issues, however, arise when the carbonate is combined...

International audience; AISI 430 stainless steel is an attractive material to be used in the healthcare industry, particularly as a sensor due to its low cost, corrosion resistance, as well as being Ni-free. AISI 430 was evaluated in an artificial sweat solution with the presence of Escherichia coli, and Staphylococcus aureus. Surface microbial analyses did not reveal colonization of bacteria on metallic surfaces, even when bacteria adhesion was investigated in a Müeller-Hinton solution. However, by electrochemical techniques, the AISI 430 surfaces demonstrated clear signs of corrosion mainly in a sterile medium after two weeks of exposure.

The oxygen reduction reaction (ORR) was investigated using two new cathode materials based on neodymium nickelate with formula Nd2-xSrxNi1-yCoyO4 ± δ (with x and y = 0 or 0.05) prepared by the citrate method. The ORR was measured in 0.5 M NaOH with a rotating disk electrode (RDE) at different rotation speeds after purging with pure oxygen. The synthesized materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), whereas the electrochemical analysis was obtained by linear voltammetry and impedance spectroscopy. The results show that before the ORR, the grains of the undoped material are spherical in shape with a size around 400 nm, while after the oxygen reduction reaction, the grain size increases. In the doped material, on the contrary, the results are reversed and the grain size becomes smaller. In addition, we show that the ORR mechanism proceeds in a single step in the undoped material while it is carried out in two successive steps in the case of the doped one. XPS analysis confirms that the sites responsible for the ORR are the OH− groups. Doping with Sr or Co does not improve the electrochemical properties: this dopant adversely affects the formation of the sites responsible for the dissociation of molecular oxygen. For larger hydroxide groups content (2.30, Nd2NiO4 ± δ) the electrochemical currents are much greater relative to that of the other Nd1.95Sr0.05Ni0.95Co0.05O4 ± δ (0.98) material. This work helps to understand the role of OH− groups, and the reduction mechanisms with 2 and 4 electrons.

Improvement of the molten carbonate fuel cell electrolyte is a key parameter to increase the performance of such electrochemical generator. One of the main challenges is to enhance the global oxygen reduction at the state-of-the-art porous nickel cathode. In this study, the effect of adding 5 mol% of caesium in Li K and Li Na molten carbonate eutectics or 5 mol% of rubidium in Li K melt was analysed with respect to the behaviour of nickel cathode towards oxygen reduction. Evolution of the open-circuit potential and electrochemical impedance spectroscopy measurements were carried out over time. In Li K melt, both Cs and Rb additives induced an improved cathode behaviour: more rapid equilibration reaching more rapidly the equilibrium potential, and significantly lower total resistance (9 times less with Cs and 3 times less with Rb), in particular mass transport, with respect to the pristine electrolyte. Moreover, charge transfer resistance was significantly lower with Rb and nearly the same with Cs versus pristine Li K. Both additions are significantly positive for enhancing oxygen reduction at the porous electrode, which seems to be particularly the case for Cs addition. However, addition of Cs to Li Na did not show an important effect. Changing the composition of Li K with the mentioned additives could be an important step towards a more performing MCFC, but more insight on oxygen reduction kinetics with Rb addition and single cell tests with both cases are compulsory.

This study addresses the problem of the nickel cathode dissolution, decreasing the lifetime of molten carbonate fuel cells, by a protective coating of Nb2O5 processed by atomic layer deposition ALD onto the porous cathode substrate. Samples of different thicknesses were tested electrochemically in molten Li2CO3-K2CO3 eutectic at 650 °C during 230 h by means of chronopotentiometry and electrochemical impedance spectroscopy. A significant decrease in the stabilization time with respect to the oxygen reduction potential is observed with niobium coatings, which could indicate an electrocatalytic process favoured by the presence of Nb. The structure and morphology of the coated samples are characterised by XRD, SEM and XPS before and after the electrochemical tests. Mixed lithiated Ni and Nb oxides are likely to be formed at the cathode surface. Interestingly, this Nb-containing mixed oxide not only can protect Ni cathode but also maintains its good performance.

Strategic views on molten carbonates : An introduction to the special issue section on the "2015 International Workshop on Molten Carbonates & Related Topics (IWMC2015), 11-13 June, 2015, Shenyang, China"

The electrochemical transformation of CO 2 into more valuable chemicals such as CO offers great interest in the energetic field. In this paper, the feasibility of this valorisation process is investigated by cyclic voltammetry in different binary molten carbonates: Li 2 CO 3 Na 2 CO 3 (52:48 mol. %), Li 2 CO 3 K 2 CO 3 (62:38 mol. %) and Na 2 CO 3 K 2 CO 3 (56:44 mol. %) and in a ternary eutectic: Li 2 CO 3 Na 2 CO 3 K 2 CO 3 (43.5:31.5:25 mol. %). The eutectic nature, the oxoacidity, temperature and scanning conditions on the reduction and oxidation peaks is thoroughly analysed. The reduction peak related to CO 2 reduction into CO is diffusion-controlled and slow quasi-reversible; in specific experimental conditions, it is split into two peaks of similar intensity. Re-oxidation peaks are most probably due to dissolved and adsorbed CO. Based on our experimental investigation under varied conditions such as molten salt composition, oxoacidity, temperature of the system and thermodynamic predictions regarding carbon presence, two mechanistic schemes are proposed, involving gaseous, dissolved and adsorbed species.

Among promising applications, LiKCO3 can be used as component of the oxide–carbonate electrolytes for low-temperature solid oxide fuel cells (LT-SOFCs), but the species ensuring the transport at the interface between the two phases is still undetermined. In view of better clarifying the role of the carbonate phase in these materials, we studied the dominant Li-related diffusion carriers and their diffusion pathways on the LiKCO3 (001) surface by density functional theory (DFT) calculations, based on the hybrid functional PBE0 for the exchange and correlation terms. Among the four different defect types considered, VLi′ was found to be the thermodynamically most stable defect in LiKCO3, but the dominant diffusion carrier was Lii+, with low diffusion barriers whose origin could be related to high O-coordination and low electrostatic repulsion arguments. The effect of the voltage applied in SOFC devices on diffusion paths was also taken into account by performing calculations in the presence of an external e...

The structural, electronic and surface properties of the mixed lithium-sodium (LiNaCO 3 ) and lithium-potassium (LiKCO 3 ) carbonates were studied through periodic calculations performed at the density functional theory (DFT) level, using three different exchange-correlation functionals. The hybrid functional PBE0 was found to be the best one to describe both geometric and electronic features of bulk LiNaCO 3 and LiKCO 3 . Polar (001) and non-polar (110) low index surfaces were taken into account, the first one being found the most stable in both cases, after reconstruction. Both introduction of vacancies (R 1 ) and octopolar terminations (R 2 ) of (001), exposing Li ((001) Li ) or Na ((001) Na ) were described in detail. The computed stability order for the reconstructed surfaces in gas phase is: (001)R1Na > > (001) R1 Li > (001) R2 Na ≈ (001) R2 Li . The obtained information, in particular regarding the electronic and surface properties, could be used in future to help understanding the role of mixed carbonates as component of oxide-carbonate electrolytes for low temperature solid oxide fuel cells (LT-SOFCs) applications, especially as reasonable starting points for dynamics calculations of liquid molten carbonates based systems.

The SOFC/SOEC community is now convinced that it is necessary to reduce the operating temperature of fuel cells to make the systems more robust, more reliable and thus to consider large-scale development. At the material level, the change of the reference electrolyte (YSZ) by a cerium compounds allows a significant performance gain for lower temperatures of use. It is obviously necessary to keep in mind the constraints related to the electrolyte application in solid electrolyte device, namely: good ionic conductivity unlike the electrical conductivity which must be low, electrochemical compatibility with the electrodes, be dense and covering on porous substrates. In this study, Gadolinia doped ceria coatings were deposited by cathodic arc evaporation from a metallic Ce-Gd (90/10 at%) target inserted into a conventional multiarc Ti evaporation target in the presence of a reactive argon-oxygen gas mixture. The structural and chemical features of these films were determined by X-ray diffraction and scanning electron microscopy. Their electrical properties were characterised using impedance spectroscopy measurements. It is shown that the as-deposited coatings crystallise in the fluorite type fcc structure of ceria and that their composition is the same than that of the target. The morphology of the coatings is influenced by the evaporation parameter (stress and droplet). The electrical measurements showed two contributions in Nyquist representation (figure1) and the activation energy is slightly higher than that given in the literature data for the bulk material. Figure 1 : Nyquist impedance plots of GDC coating, registered at 400°C, for two a.c. signal amplitudes. Logarithms of frequencies are indicated in the figure. Figure 1

This paper is dedicated to the impact of pressure on the electrochemical behaviour of LSCF (La1-xSrxCoyFe1-yO3-δ) anode in high-temperature electrolysers. This study was carried out with symmetrical cells associating LSCF electrodes to a 3YSZ (yttrium-stabilised zirconia) electrolyte. Impedance spectroscopy measurements were performed using a three-electrode configuration, at temperature as high as 700 to 800 °C, in a pressure range from 1 to 30 bar. A clear improvement in terms of electrode resistance decrease is highlighted, mainly due to faster oxygen adsorption/desorption kinetics and a better supply of gas to electrochemical reaction sites. Other assumptions were considered and analysed, such as the impact of pressure on LSCF electrical conductivity and on the mechanical contacts. Thus, three contributions were determined as limiting steps at low pressure, up to 5 bar, whilst for higher pressure, the optimised conditions in operation are reached. This study completes a previous one related to a modelling approach.

International audience; In this work, La2NiO4+δ is used as cathode material for Intermediate temperature solid oxide fuel cells (IT-SOFC). Scanning electron microscopy, X-ray diffraction, and electrochemical impedance spectroscopy are used to investigate the effect of the presence of an ultrathin La2NiO4+δ layer (80 nm) deposited by dip-coating or sputtering at the interface YSZ/La2NiO4+δ. The thick porous cathode layer of La2NiO4+δ is deposited by screen-printing, and sintered at 1000 °C for 2 h or 1200 °C for 20 min in order to study the effect of sintering temperature on the electrochemical properties. The results show that the electrochemical performances of the cathode are influenced by the deposition technique. The best electrochemical properties are obtained with the use of the nano film interface layer deposited by sputtering. The introduction of ultrathin interface with nano grained between the cathode and electrolyte is a promising technique to reduce polarization resistance associated with oxygen reduction reaction (ORR) on the cathode.

A comprehensive density functional theory investigation of conduction mechanisms of both intrinsic and extrinsic species found in oxide–carbonate composite electrolyte materials used in solid oxide...

Correction for ‘Modeling composite electrolytes for low-temperature solid oxide fuel cell application: structural, vibrational and electronic features of carbonate–oxide interfaces’ by Chiara Ricca et al., J. Mater. Chem. A, 2016, DOI: 10.1039/c6ta06827h.

Optimization of the molten carbonate electrolyte is the most challenging topic in order to increase the lifetime and performance of the molten carbonate fuel cell (MCFC). Besides controlling electrolyte properties such as stability, conductivity, volatility, surface tension, molar volumes etc., it is mandatory to reduce the dissolution of the LixNi1−xO state-of-the-art cathode. Furthermore, the nature of the eutectic also may influence the electrode kinetics and, in particular, at the cathode side where the reduction reaction is known to be slow. The conventional molten salt used in MCFC devices is composed by Li2CO3–K2CO3 (62/38 mol%), which has a better performance at temperatures below 600 °C than Li2CO3/Na2CO3 (52/48 mol%) electrolyte but presents a higher Ni solubility than the Li–Na electrolyte. To improve the properties of the Li–K eutectics towards the ORR (oxygen reduction reaction), heavy alkali cations such as Cs or Rb can be used as additives in the electrolyte. The present work is dedicated to a thorough analysis of the oxygen reduction kinetics in Li2CO3–K2CO3 (62/38 mol%) eutectic containing small amounts of Cs2CO3 by means of impedance spectroscopy and fitting performed using Warburg and Gerischer models, showing the favourable effect of this additive and convenience between the two model approaches.

Phases constituted by La2-x Cu x NiO4±δ (0.01 ≤ x ≤ 0.1) of the Ruddlesden-Popper family (La n+1Ni n O3n+1; n = 1) were prepared and then mixed with La4Ni3O10, in a weight ratio of 50:50 wt%, in order to be used as solid oxide fuel cell cathodes. ASR values relative to the symmetrical cells constituted by yttria-stabilized zirconia electrolyte and the following electrodes, La1.98Cu0.02NiO4+δ + La4Ni3O10 and La1.95Cu0.05NiO4+δ + La4Ni3O10, are of 11.8 Ω cm2 at 650 °C for both and, respectively, of 3.5 and 2.9 Ω cm2 at 750 °C. In the case of the second cell, the electrode material reacts with the electrolyte forming an insulating phase at the interface, contrarily to the first cell, which stability could be explained by the combination of low doping amounts of copper and the presence of La4Ni3O10 acting as a stabilizer of the material at high temperature.

In order to improve the industrial attractiveness of high temperature steam electrolysis (HTSE), increasing the operating pressure is one of the most promising solutions. In this context, this study is dedicated to the analysis of the pressure influence on the electrochemical reactions occurring in HTSE. The behavior of half-cells constituted by YSZ electrolytes and Ni/YSZ cathodes or LSCF anodes was simulated by COMSOL multiphysics ® . This model highlights that the limiting current density due to the lack of steam is shifted towards higher steam conversion rates by increasing the operating pressure, without negative thermodynamic effect at high current density. Furthermore, the overpressure at the oxygen electrode/electrolyte interface decreases with the operating pressure and, therefore, the risk of delamination is reduced. Experimentally, a positive effect of pressure on the oxygen side performances was observed, contrarily to the model calculation.