Boosting the electrochemical performance of micro-tubular solid oxide fuel cell via the microstructure regulation

Microtubular anode-supported solid oxide fuel cells (μt-SOFC) were created with a metallic coil embedded in the anode to act as current collector. The electrochemical performance was experimentally examined by comparing the power density (PD) of μt-SOFC with embedded coils of different turns per unit length and composition (nickel and palladium). It is shown that an increase in the turns per unit length results in a proportional current density increase and in a quadratic increment of PD. Additional performance improvement is found for the cell with palladium current collector due to the higher catalytic activity for hydrogen oxidation.

We aim to mitigate the spatial temperature variations contributing to the thermal stresses in solid oxide fuel cells. We thus analyze the involving processes through spatial temperature, current, and impedance variations in-situ measured by the electrode-segmentation method in a microtubular solid oxide. We find that, despite the preheating, the excess air flow commonly supplied in the practical applications for the convective cooling is the prevailing factor on the temperature variations causing a significant temperature gradient in the air inlet region, that poses a high risk of mechanical failure. In terms of the flow configuration, counter-flow shows larger temperature and current variations. The impedance variations clarify the impact of the temperature distribution on the current variations. Namely, high temperature in the fuel upstream accompanied with the high hydrogen concentration boosts the local current density, thus, results in larger Nernst-loss in the downstream wherein temperature is lower as well. We conclude that the excess air flow indirectly contributes to the thermal stresses and thus we recommend the reduction of the excess flow.

A growing interest in the development of solid oxide electrochemical systems, including solid oxide fuel cell (SOFC) and solid oxide electrolyser cells (SOEC) has increased the demand for new electrode materials that can offer superior electrochemical performance. The misfit-layered Ca cobaltite ([Ca2CoO3-δ]0.62[CoO2], C349) has emerged as a potential oxygen electrode for solid oxide cells (SOCs), in recent years, due to its optimal electrical conductivity (~100 S cm-1, from room temperature to 800 °C), excellent thermal compatibility with typical electrolyte materials, its low cost and its avoidance of Sr surface segregation issues that can deplete the electrochemical performance in more common oxygen electrodes 1,2. Its structure consists of two monoclinic subsystems of layers of Ca2CoO3 (three-layered rock salt-type block, CaO-CoO-CaO) and CoO2 (triangular lattice), stacked along the c-axis 3. This compound offers mixed ionic and electronic conduction (MIEC), where the first subsystem is responsible for the ionic conductivity, due to its higher oxygen deficiency, while the second subsystem is responsible for the electronic behaviour. Nonetheless, the level of ionic conductivity of C349 is, comparatively, low, and this factor has prevented it from attaining a competitive electrode performance 4, to date when compared to peak electrode materials, such as La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF). For this reason, we overcome this limitation in this study by the addition of a predominately ion-conducting phase with a minor p-type electron-conductivity, Ce0.8Pr0.2O1.9 (CPO) to the C349 material. This new composite electrode is compared against the standard, high performing, electrode material LSCF in terms of microstructure, film thickness, and subsequent electrochemical properties.Symmetrical cell assemblies were fabricated by a cheap and simple screen-printing technique using Ce0.9Gd0.1O1.95 electrolytes and repeated depositions were performed to investigate the electrode thickness effect.A minimum R p value can be found for the C349-based electrodes with 5 depositions (70 – 85 μm). By comparison to the state-of-the-art LSCF electrode, C349 has been shown to require a higher solid volume fraction close to the electrolyte/electrode interface for continuing to maximise the penetration of the ionic current into the electrode bulk and for extending the electrochemically active region for oxygen exchange at the gas/electrode interface. The presence of a higher solid fraction of material benefits the oxygen exchange/reaction processes, with additional surface diffusion. Furthermore, the addition of CPO to the C349 electrode is shown to dramatically lower its polarisation resistance, allowing this composite to achieve a competitive electrochemical performance to that of the state-of-the-art LSCF electrode (0.37 and 0.52 Ω·cm2, at 700 °C in oxygen atmosphere, respectively). Overall, a Gerischer contribution can explain the experimental R p of the electrodes (except in the case of the C349 sample with just one deposition). These results are further supported by a detailed mechanistic study, based on a Distribution Function of Relaxation Times (DFRT) analysis, to understand the origin of this improvement as a function of electrode morphology and composition.The successful outcome of this work is extremely important as it provides not only a highly competitive new electrode composition, but also valuable insight into future optimisation methods for similar new mixed ionic-electronic conducting electrodes that intrinsically suffer from low levels of oxygen diffusion. AcknowledmentsThis study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001. Allan J. M. Araújo acknowledges the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq/Brazil, reference number 200439/2019-7). João P. F. Grilo, Carlos A. Paskocimas and Daniel A. Macedo also thank CNPq/Brazil (482473/2010-0, 446126/2014-4, 308548/2014-0, 307236/2018-8, 431428/2018-2 and 309430/2019-4). Laura I. V. Holz acknowledges Fundação para a Ciência e Tecnologia (FCT) for the PhD grant PD/BDE/142837/2018. The authors also acknowledge the projects, PTDC/CTM-CTM/2156/2020, PTDC/QUI-ELT/3681/2020, POCI-01-0247-FEDER-039926, POCI-01-0145-FEDER-032241, UIDB/00481/2020 and UIDP/00481/2020 and CENTRO-01-0145-FEDER-022083 - Centro Portugal Regional Operational Programme (Centro2020), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (ERDF). References1 K. Nagasawa, S. Daviero-Minaud, N. Preux, A. Rolle, P. Roussel, H. Nakatsugawa and O. Mentré, Chem. Mater., 2009, 21, 4738–4745.2 S. P. Simner, M. D. Anderson, M. H. Engelhard and J. W. Stevenson, Electrochem. Solid-State Lett., 2006, 9, A478–A481.3 M. Schrade, H. Fjeld, T. G. Finstad and T. Norby, J. Phys. Chem. C, 2014, 118, 2908–2918.4 V. Thoréton, Y. Hu, C. Pirovano, E. Capoen, N. Nuns, A. S. Mamede, G. Dezanneau, C. Y. Yoo, H. J. M. Bouwmeester and R. N. Vannier, J. Mater. Chem. A, 2014, 2, 19717–19725.

Solid Oxide Electrolysis Cells (SOECs) play a key role in power-to-gas applications as a relevant electrochemical conversion device for addressing the global energy crisis. It uses electrical energy to transform naturally abundant chemicals like H2O or CO2 into high energy-density or industrially relevant gases such as H2, CO, and CH4 [1].The current SoA fuel electrode materials: Ni-YSZ and Ni-GDC, enable efficient electrochemical reactions at high temperatures (600°C–900°C). However, when operating at high current density, they exhibit some serious issues such as nickel migration and agglomeration, which ultimately reduce the SOEC durability and lifetime [2], [3]. As a result, researchers are investigating Ni-free mixed ionic-electronic conductor (MIEC) based fuel electrode materials, for example, perovskites or single-phase doped ceria [4], [5].In this context, recent studies on single-phase gadolinium-doped ceria (GDC) fuel electrodes have demonstrated improved durability and electrochemical performance over Ni-YSZ; however, it is still a challenge to surpass the electrochemical performance and durability of single-phase doped ceria over Ni-GDC [6], [7]. To address this issue, this research explores the potential of incorporating single-phase praseodymium-doped ceria (PDC) as an alternative fuel electrode material. Specifically, three concentrations of doped ceria materials: 5% lanthanum and 5% praseodymium doped ceria (LPDC: La0.05Pr0.05Ce0.9O2-δ), 10% praseodymium doped ceria (PDC10: Pr0.1Ce0.9O2-δ), and 30% praseodymium doped ceria (PDC30: Pr0.3Ce0.7O2-δ) were used as fuel electrode to fabricate electrolyte-supported single cells. The cell denomination for the LPDC, PDC10, and PDC30 based single cells are LPDC/GDC/8YSZ/GDC/LSCF, PDC10/GDC/8YSZ/GDC/LSCF, and PDC30/GDC/8YSZ/GDC/LSCF, respectively.At 900°C, under steam electrolysis conditions: 50% H2 + 50% H2O, PDC10 outperforms both LPDC (-1.37 A/cm²) and PDC30 (-1.1 A/cm²), achieving a current density of -1.5 A/cm² at 1.5 V (see attached figure) [6], [8], [9]. In addition, the electrochemical performance (I-V characteristics and EIS) was investigated. The structural and chemical properties of these three materials were also analyzed using XRD, TGA, Raman spectroscopy, and XPS to evaluate their physicochemical behaviour at a fundamental level.In conclusion, these results suggest that single-phase praseodymium doped ceria-based materials could be a promising alternative in the search for efficient and durable Ni-free fuel electrode materials for SOECs. Literature:[1] A. Hauch et al., “Recent advances in solid oxide cell technology for electrolysis,” Science (1979), vol. 370, no. 6513, Oct. 2020, doi: 10.1126/science.aba6118.[2] C. Graves, S. D. Ebbesen, S. H. Jensen, S. B. Simonsen, and M. B. Mogensen, “Eliminating degradation in solid oxide electrochemical cells by reversible operation,” Nat Mater, vol. 14, no. 2, pp. 239–244, 2015, doi: 10.1038/nmat4165.[3] D Simwonis, F. Tietz, D. Stover, and S. Stover, “Nickel coarsening in annealed Ni / 8YSZ anode substrates for solid oxide fuel cells In memoriam to Professor H. Tagawa,” 2000.[4] S. E. Wolf et al., “Solid oxide electrolysis cells - current material development and industrial application,” Jul. 10, 2023, Royal Society of Chemistry. doi: 10.1039/d3ta02161k.[5] E. M. Sala et al., “Unravelling the role of dopants in the electrocatalytic activity of ceria towards CO2 reduction in solid oxide electrolysis cells,” Physical Chemistry Chemical Physics, vol. 25, no.4, pp. 3457–3471, Jan. 2023, doi: 10.1039/d2cp05157e.[6] J. Uecker, I. D. Unachukwu, V. Vibhu, I. C. Vinke, L. G. J. de Haart, and R. A. Eichel, “Gadolinium Doped Ceria as Nickel–Free Fuel Electrode in High Temperature CO2-Electrolysis,” ChemElectroChem, 2024, doi: 10.1002/celc.202300617.[7] A. Nenning, M. Holzmann, J. Fleig, and A. K. Opitz, “Excellent kinetics of single-phase Gd-doped ceria fuel electrodes in solid oxide cells,” Mater Adv, vol. 2, no. 16, pp. 5422–5431, Aug. 2021, doi: 10.1039/d1ma00202c.[8] I. D. Unachukwu, V. Vibhu, I. C. Vinke, R. A. Eichel, and L. G. J. (Bert) de Haart, “Electrochemical and degradation behaviour of single cells comprising Ni-GDC fuel electrode under high temperature steam- and co-electrolysis conditions,” J Power Sources, vol. 556, Feb. 2023, doi: 10.1016/j.jpowsour.2022.232436.[9] I. D. Unachukwu, V. Vibhu, J. Uecker, I. C. Vinke, R.-A. Eichel, and L. G. J. (Bert) de Haart, “ Comparison of the Electrochemical and Degradation Behaviour of Ni-YSZ and Ni-GDC Electrodes Under Steam, Co- and CO2 Electrolysis ,” ECS Trans, vol. 111, no. 6, pp. 1445–1452, May 2023, doi: 10.1149/11106.1445ecst. Figure 1

Theoretical studies on the electrochemical and mechanical properties and microstructure optimization of micro-tubular solid oxide fuel cells

Reversible solid oxide cells (RSOCs) represent a promising technology for the efficient exploitation of intrinsically intermittent renewable energy sources. RSOCs allow to derive fuel and chemicals from power (power-to-gas technology, P2G) and power from fuel and chemicals (gas-to-power technology, GTP) and can be interchangeably operated either as a solid oxide fuel cell (SOFC) or as a solid oxide electrolyzer cell (SOEC). The key aspect to render these devices competitive on a market scale is the development of multi-tasking, reliable, cost-effective and long-lasting electrodes (1,2). Besides, to overcome the issues related to hydrogen production, storage and distribution (e.g. impractical conversion of the existing grid to hydrogen-based infrastructures), the fuel-electrode of RSOCs should ensure high catalytic activity and coking resistance toward carbon-containing species (3-4). Using a hydrocarbon-tolerant fuel electrode, energy can be obtained by natural gas and biogas (SOFC-mode), with useful recovery of CO2 in the exhausts (carbon capture and storage, CCS). Besides, if the electrode is also active towards CO2 electrolysis (SOEC mode), CO2 is reduced to CO and O2 (carbon capture and utilization, CCU).Ni-YSZ is the reference fuel-electrode material for both H2 fed SOFC and for CO2 electrolysis in SOEC. Nevertheless, Ni-based cermets cannot be used in SOFCs fed with methane-containing fuels, as they suffer from two main drawbacks: mechanical instability upon NiO-Ni redox cycles (5) and passivation due to coking, being Ni a catalyst for methane cracking (3, 4). Moreover, during Ni-YSZ operation in CO2-SOEC mode, ZrO2 reduction can occur at high cathodic potential, resulting in Ni-Zr compounds formation (6).In this work, a recently developed (7, 8) composite material containing La0.6Sr0.4Fe0.8Mn0.2O3-δ (LSFMn) and 5wt% Ni-containing Ce0.58Sm0.15O2-δ (NiSDC) is tested as fuel electrode for LSGM-electrolyte supported cells. In reducing conditions, Fe exsolved from the LSFMn perovskite forms a Fe-Ni alloy with Ni present on SDC. In SOFC mode, the composite is designed to operate in dry methane: Fe-Ni catalytic sites activate CH4, which is successively oxidized on Mn-containing LSFMn, while SDC increases the O2- supply at the anode to get rid of any carbonaceous deposits. As Fe-Ni alloy was reported to be highly active for CO2 reduction (9), the composite was also tested as SOEC cathode in different CO2:CO ratios. LSFMn+NiSDC was tested in SOFC-mode as anode for hydrogen, dry methane and carbon monoxide oxidation and showed power density outputs of 657, 668 and 527 mW/cm2, respectively (Fig. a), a redox stable behavior and coking resistance for over 120 h. LSFMn+NiSDC in SOEC-mode delivered 2.66 A/cm2 at 2 V in 95:5 CO2:CO mixture (Fig. b), keeping 1 A/cm2 of current density output for over 40 h. (1) - M. Mogensen, M. Chen, H. Frandsen, C. Graves, J. Hansen, K. Hansen, A. Hauch, T. Jacobsen, S. Jensen, T. Skafte, Reversible solid-oxide cells for clean and sustainable energy, Clean Energy, 3 (2019) 175-201. (2) - M.B. Mogensen, Materials for Reversible Solid Oxide Cells, Current Opinion in Electrochemistry, (2020). (3) - M. Mogensen, K. Kammer, Conversion of hydrocarbons in solid oxide fuel cells, Annual Review of Materials Research, 33 (2003) 321-331. (4) - S. McIntosh, R.J. Gorte, Direct hydrocarbon solid oxide fuel cells, Chemical reviews, 104 (2004) 4845-4866. (5) - J. Malzbender, R. Steinbrech, Advanced measurement techniques to characterize thermo-mechanical aspects of solid oxide fuel cells, Journal of Power Sources, 173 (2007) 60-67 (6) - A. Hauch, K. Brodersen, M. Chen, M.B. Mogensen, Ni/YSZ electrodes structures optimized for increased electrolysis performance and durability, Solid State Ionics, 293 (2016) 27-36 (7) - L. Duranti, I. Luisetto, S. Licoccia, C. Del Gaudio, E. Di Bartolomeo, Electrochemical performance and stability of LSFMn+ NiSDC anode in dry methane, Electrochimica Acta, (2020) 137116. (8) - L. Duranti, I.N. Sora, F. Zurlo, I. Luisetto, S. Licoccia, E. Di Bartolomeo, The role of manganese substitution on the redox behavior of La0.6Sr0.4Fe0.8Mn0.2O3-δ, Journal of the European Ceramic Society, (2020) ( 9 ) - Liu, S., Liu, Q., & Luo, J. L. (2016). Highly stable and efficient catalyst with in situ exsolved Fe–Ni alloy nanospheres socketed on an oxygen deficient perovskite for direct CO2 electrolysis. ACS Catalysis, 6(9), 6219-6228. Figure 1

Solid oxide cells (SOCs), both solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC), have being attracting more and more attention due to its high energy conversion efficiency and fuel flexibility. However, degradation of fuel electrodes after long-term operation remains as one of the main challenges for their commercial application. In particular, migration and coarsening of nickel (Ni) in Ni - yttria-stabilized zirconia (Ni-YSZ) fuel electrodes have strong impacts on the decreases in both active three-phase boundary (TPB) and Ni network connectivity, which result in performance deterioration. One of the mechanisms proposed as an explanation of Ni migration is Ni transport via volatile Ni(OH)x species, so-called evaporation-condensation mechanism [1]. On the other hand, Jiao and Shikazono [2] proposed a model to explain Ni spreading on YSZ surface based on the variation of Ni-YSZ wettability which is modified by the oxygen adsorption. Nevertheless, further investigations are required to understand the mechanisms of Ni migration. In the present study, Ni-film patterned electrodes which can provide well defined TPB configurations are used to investigate the Ni-YSZ degradation under SOFC, SOEC and sequential SOFC and SOEC operations, i.e. reversible operation (RSOC). The edge of sputtered Ni-film contacting with open YSZ surface can be treated as active TPB during operation. Confocal laser scanning microscopy (CLSM, Keyence, VK-X 1000) is used, which enabled in-operando observation of the real-time local morphological change at active TPB [3]. The in-operando potentiostatic experiment was carried out inside a high temperature chamber which was kept at 800oC with 4% H2O-4% H2-92% N2 as fuel gas and 30% O2-70% N2 as oxidant as shown in Fig. 1(a). The correlations between the Ni morphological changes and cells’ electrochemical performances were investigated. The Ni phase dynamically spread and de-percolated only under the SOFC operation, while such a phenomenon was not observed during the SOEC operation, as shown in Figs. 1(c), (d) and (e). Ni coarsening occurred regardless of the operation modes. The competition between Ni-film spreading and breaking-up finally determined the complicated local morphological change and corresponding cell performance variation. The time variations of active TPB and current density showed good correlation as shown in Fig. 1(b). Real-time in-operando observations revealed different Ni migration under SOFC, SOEC and RSOC operations, which may provide new insights for the understanding of Ni-YSZ fuel electrode degradation.Fig. 1. (a) Schematic illustration of in-operando setup. (b) Correlation between current density and Ni morphological evolution. (c)-(e) CLSM images and 3D surface height contour maps of the yellow-frame-enclosed areas after SOFC, SOEC and RSOC modes, respectively.

Electrochemical performance and long-term durability of a 200 W-class solid oxide regenerative fuel cell stack

Transport of reactants and products to/from reactions sites affects the electrochemical energy conversion performance of fuel cells substantially. At high reactant utilization rates, mass transport can be the performance limiting factor, resulting in significant variations of current and temperature, etc. in the active field. To overcome mass transport limitations, reactants can be supplied at high rates and proper flow fields can be designed, for both of which numerical simulations are quite valuable. In these regards, although the highest care is put on the transport of species within active area of cells/stacks, herein we show the onset of mass transport limitation in the inlet periphery, i.e., extension of the concentration gradient of reactants from reactions sites inward the inlet periphery at high reactant utilization rates. We clarify this phenomenon leaning upon the computational error appearing in the concentration profile of a microtubular Solid Oxide Fuel Cell (SOFC) while simulating its electrochemical performance. For eliminating this error in numerical studies of fuel cells, we propose and demonstrate a practical method. We also determine the critical ratio of consumed/supplied mass fluxes for evaluating relevant (reactant species) SOFC systems in terms of the mass transport limitation in their inlet peripheries.

Rare-earth nickelates Ln2NiO4+ δ (Ln = Pr, Nd) with perovskite-related structure are very promising cathodes materials for SOFCs (Solid Oxide Fuel Cells) due to their high ionic and electronic conductivities as well as their electrocatalytic properties.1 Theses phases crystallize in the a Ruddlesden-Popper (RP) structure, with the intergrowth of n LnNiO3 perovskite layers for one NaCl-type LnO layer. Electronic conductivity is provided by the NiO6 octahedra in the perovskite layer, while anionic diffusion takes place mainly via interstitial oxygen sites in the NaCl layer.Neodymium nickelate (Nd2NiO4+ ⸹) exhibits excellent chemical stability and a moderately good electrochemical performance. In contrast, praseodymium nickelate Pr2NiO4+ ⸹ , presents a very low ASR (Area Specific Resistance) but shows a limited chemical stability especially during SOFC operation. Aiming to find a trade-off between the high electrochemical performance of Pr2NiO4+ ⸹ and the excellent chemical stability of Nd2NiO4+ ⸹, the solid solution with the general formula Nd2-xPrxNiO4+ ⸹ (x = 0.5, 1, and 1.5) has been studied. The different compositions were successfully synthesised via the citrate-nitrate route. The solid solution was characterised by XRD, and the lattice parameters exhibit intermediate values between those of Pr2NiO4+ ⸹ and Nd2NiO4+ ⸹. Their crystallographic structure was studied and the oxygen content of each material was measured. The electrochemical performances measured on symmetrical cells showed lower ASR values for the NdPrNiO4+ ⸹ compound.For further investigations, we aimed to introduce a limited cation vacancies amount into the lanthanide (Ln) sub-lattice, which could influence the oxygen non-stoichiometry, the electronic structure and conductivity as well as the electro-catalytic activity. Original compositions such as (NdPr)2-xNiO4+ ⸹ with x = 0, 0.05, 0.1 were successfully prepared. The electrochemical performance studies carried on the corresponding half symmetrical cells showed an ASR of 40 mΩ.cm2 at 700 °C, i.e; among the best ones reported in the literature. Ageing measurements are currently in progress. Morales-Zapata, M. A., Larrea, A. & Laguna-Bercero, M. A. Lanthanide nickelates for their application on Solid Oxide Cells. Electrochimica Acta 444, 141970 (2023).

A high performance air electrode was fabricated by infiltration of nano-catalysts into a porous backbone for high-temperature solid oxide regenerative fuel cells (SORFCs). The Sm0.5Sr0.5CoO3 (SSC) nano-catalysts were uniformly synthesized in a porous La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) – gadolinia-doped ceria (GDC) composite backbone by impregnation of nitrate precursor solution followed by homogeneous nucleation induced by urea decomposition. Significant improvement in the electrochemical performance was achieved in both solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes.

Solid oxide fuel cells and solid oxide electrolysis cells have emerged as promising technologies for efficient energy conversion and storage, offering clean electricity generation and valuable chemical production. Recent research has focused on developing electrode-supported cells with electrolyte thicknesses reduced to below 3μm. This approach is based on the theoretical expectation that reducing electrolyte thickness will decrease electrolyte resistance and enhance cell performance.However, since electrodes have a porous structure, their contact with the electrolyte is imperfect, leading to higher measured electrolyte resistance than theoretically predicted as electrolyte thickness decreases. Despite this phenomenon, systematic studies investigating its impact on electrolyte conductivity analysis remain limited. Furthermore, yttria-stabilized zirconia (YSZ), commonly used as an electrolyte, requires a buffer layer such as gadolinium-doped ceria (GDC) to prevent reactions with the LSCF air electrode. During sintering, reactions between YSZ and GDC increase electrolyte resistance. These combined factors inevitably result in higher electrolyte resistance than theoretical values. However, in this configuration, distinguishing between resistance increases due to the imperfect electrode contact and YSZ/GDC reactions remains challenging, and comprehensive studies considering both factors are scarce.In this study, we systematically analyzed the impact of imperfect contact from porous electrodes on electrolyte conductivity and the resistance caused by electrolyte-buffer layer reactions. We fabricated dense GDC/YSZ/GDC cells at different sintering temperatures to quantitatively evaluate and distinguish between interfacial effects of electrode-electrolyte contact and YSZ/GDC interfacial reactions. Results showed that electrode contact effects become significant as electrolyte thickness and sintering temperature decreases, indicating that electrode contact effects must be considered when improving performance through electrolyte thickness reduction. This study reveals the critical relationship between electrochemical performance and the combined effects of electrode contact and buffer layer-electrolyte reactions.

Solid oxide cells (SOCs) are highly efficient and environmentally benign devices that can be used to store renewable electrical energy in the form of fuels such as hydrogen in the solid oxide electrolysis cell mode and regenerate electrical power using stored fuels in the solid oxide fuel cell mode. Despite this, insufficient long-term durability over 5–10 years in terms of lifespan remains a critical issue in the development of reliable SOC technologies in which the surface segregation of cations, particularly strontium (Sr) on oxygen electrodes, plays a critical role in the surface chemistry of oxygen electrodes and is integral to the overall performance and durability of SOCs. Due to this, this review will provide a critical overview of the surface segregation phenomenon, including influential factors, driving forces, reactivity with volatile impurities such as chromium, boron, sulphur and carbon dioxide, interactions at electrode/electrolyte interfaces and influences on the electrochemical performance and stability of SOCs with an emphasis on Sr segregation in widely investigated (La,Sr)MnO3 and (La,Sr)(Co,Fe)O3−δ. In addition, this review will present strategies for the mitigation of Sr surface segregation.Graphic

The present study is focused on the development of alternative oxygen electrodes for Solid Oxide Fuel Cells (SOFCs) and Solid Oxide Electrolyzers Cells (SOECs). Rare earth nickelates with general formula Ln2NiO4+δ (Ln = La, Pr or Nd) have shown good performance as oxygen electrodes with various electrolytes. To further enhance the physico-chemical properties, electrochemical performance as oxygen electrode and durability of Solid Oxide Cells (SOCs), herein, we have performed the substitution of nickel with cobalt in these nickelates. Two compositions (x=0.1 and 0.2) were mainly considered and completely characterized using several techniques. The single cells were then prepared and electrochemically characterized using DC- and AC-techniques in the temperature range 700-900 °C. The durability test up to 250h were also investigated at 1 A.cm-2 current density at 800 °C under both SOFC (dry conditions) and SOEC conditions (with 50% H2 and 50% H2O feed gas mixture) indicating different degradation behavior.

Current status, research trends, and challenges in water electrolysis science and technology