Study of Pr and Pr and Co doped La2NiO4+δ as cathodes for La5.5WO11.25-δ based protonic conducting fuel cells

[EN] The mixed ionic-electronic conductor La2NiO4+delta was investigated as potential cathode material for protonic conducting solid oxide fuel cells (PC-SOFCs) based on La5.5WO11.25-delta electrolyte. Firstly the chemical compatibility between cathode and electrolyte phases (La2NiO4+delta and La5.5WO11.25-delta respectively) was studied. Then, the electrochemical properties of this cathode were improved by partially substituting La and/or Ni, specifically La1.5Pr0.5NiO4+delta and La(1.5)Pro(0.5)Nio(0.8)Co(0.2)O(4+delta) were considered. These two doped materials showed improved electrical conductivity and reduced polarization resistance, when tested as cathode in symmetrical cells. In a second step, the microstructure of La(1.5)Pro(0.5)Nio(0.8)Co(0.2)O(4+delta) was optimized by varying the firing temperature of the cathode. The performance of these mixed conductors is limited by medium frequencies associated processes while they show lower polarization resistances (Rp) than conventional composites based on La5.5WO11.25-delta and pure electronic conductors. La(1.5)Pro(0.5)Nio(0.8)Co(0.2)O(4+delta) cathode sintered at 1050 degrees C exhibits the best electrochemical performance on a La5.5WO11.25-delta-based PC-SOFC, achieving Rp = 0.62 Omega cm(2) at 750 degrees C in wet air.Funding from European Union (FP7 Project EFFIPRO - Grant agreement 227560), the Spanish Government (ENE2011-24761, SEV-2012-0267, BES-2012-053180 and CSIC Intramural 200880I093 grants) is kindly acknowledged. The authors thank M. Fabuel for sample preparation.Solis Díaz, C.; Navarrete Algaba, L.; Serra Alfaro, JM. (2013). Study of Pr and Pr and Co doped La2NiO4+δ as cathodes for La5.5WO11.25-δ based protonic conducting fuel cells. Journal of Power Sources. 240:691-697. https://doi.org/10.1016/j.jpowsour.2013.05.055S69169724

Comparative Study of Epoxy-CsH2PO4 Composite Electrolytes and Porous Metal Based Electrocatalysts for Solid Acid Electrochemical Cells

[EN] Electrochemical cells based on acid salts (CsH2PO4) have attracted great interest for intermediate temperature, due to the outstanding proton conductivity of acid salts. In this work, electrodes and electrolyte were optimized following different strategies. An epoxy resin was added to the CsH2PO4 material to enhance the mechanical properties of the electrolyte, achieving good conductivity, enhanced stability, and cyclability. The electrodes configuration was modified, and Ni sponge was selected as active support. The infiltration of different oxide nanoparticles was carried out to tailor the electrodes resistance by promoting the electrocatalyst activity of electrodes. The selection of a cell supported on the electrode and the addition of an epoxy resin enables the reduction of the electrolyte thickness without damaging the mechanical stability of the thinner electrolyte.Funding from Spanish Government (MINECO ENE2014-57651 grant) is kindly acknowledged. We greatly appreciated using the Convergence Research Laboratory (established by the MNU Innovation Support Project in 2020) to conduct this research. This work was financially supported by the Spanish Government (Grants SEV-2016-0683 and RTI2018-102161) and the Generalitat Valenciana (PROMETEO/2018/006). The authors want also to acknowledge the Electron Microscopy Service from the Universitat Politècnica de València for their support in the SEM analysis performed in this work.Navarrete Algaba, L.; Yoo, C.; Serra Alfaro, JM. (2021). Comparative Study of Epoxy-CsH2PO4 Composite Electrolytes and Porous Metal Based Electrocatalysts for Solid Acid Electrochemical Cells. Membranes. 11(3):1-14. https://doi.org/10.3390/membranes11030196S11411

Electrochemical properties of composite fuel cell cathodes for La5.5WO12−δ proton conducting electrolytes

[EN] New composite cathodes for proton conducting solid oxide fuel cells (PC-SOFCs) based on the novel La5.5WO12-delta (LWO) electrolyte have been developed. First the applicability of LWO as a protonic electrolyte has been proved by recording the OCV in a Pt/LWO/Pt cell as a function of the temperature, matching the expected Nernst voltage. In order to improve the electrode performance on LWO PC-SOFCs, composite cathodes have been prepared by mixing the La0.8Sr0.2MnO3-delta (LSM) electronic phase with the LWO protonic phase. The ceramic-ceramic (cer-cer) composites have been electrochemically studied as cathodes on LWO dense electrolytes in symmetrical cells. Different ratios of both phases and two different electrode sintering temperatures (1050 and 1150 degrees C) have been studied. Electrochemical impedance spectroscopy (EIS) analysis has been carried out in the temperature range 700-900 degrees C under moist (2.5% H2O) atmospheres. Different oxygen partial pressures (pO(2)) have been employed in order to characterize the processes (surface reaction and charge transport) taking place at the composite cathode. A substantial improvement in the cathode performance has been attained by the addition of the LWO protonic phase into the LSM electronic material. From the electrochemical analysis it can be inferred that electrode enhancement is principally ascribed to the increase in the three-phase-boundary length, which enables electrochemical reactions to occur along the thickness of the electrode.Funding from European Union (FP7 Project EFFIPRO - Grant Agreement 227560), the Spanish Government (ENE2011-24761 and CSIC Intramural 200880I093 grants) is kindly acknowledged. The authors thank Dr M. Ivanova and Dr D. Sebold (Forschungszentrum Julich, IEK-1) for sample preparation for microscopy analysis, and Mrs M. Fabuel and Dr V. B. Vert for assistance in electrochemical tests.Solis Díaz, C.; Navarrete Algaba, L.; Roitsch, S.; Serra Alfaro, JM. (2012). Electrochemical properties of composite fuel cell cathodes for La5.5WO12−δ proton conducting electrolytes. Journal of Materials Chemistry. 22(31):16051-16059. https://doi.org/10.1039/c2jm32061d1605116059223

Optimization of SOFC Composite Cathodes Based on LSM and Doped Cerias Ce0.8Ln0.2O2 (Ln = Gd, Er, Tb and Pr)

[EN] Composites made of La0.8Sr0.2MnO3-delta (LSM) and lanthanide doped ceria (Ce(0.8)Ln(0.2)O(2-delta), Ln = Gd, Er, Tb and Pr) have been proposed as robust and high-performing solid oxide fuel cell cathodes. The addition of small amounts of highly-dispersed CoOx into the electrode promoted the formation of bridges among LSM-ceria particles. These resulted in the reduction of the required sintering temperature due to the enhancement of the sintering and proper ionic and electronic percolation pathways. In addition, Pr as a multivalent cation dopant in ceria showed the best electrochemical results toward oxygen reduction when the electrode sintering temperature is kept at 1000 degrees C. (C) 2016 The Electrochemical Society. All rights reserved.This work was supported by funding from Spanish Government (MINECO) (SEV-2012-0267 and ENE2014-57651 grants).Navarrete Algaba, L.; Balaguer Ramírez, M.; Vert Belenguer, VB.; Serra Alfaro, JM. (2016). Optimization of SOFC Composite Cathodes Based on LSM and Doped Cerias Ce0.8Ln0.2O2 (Ln = Gd, Er, Tb and Pr). Journal of The Electrochemical Society. 163(13):1440-1443. https://doi.org/10.1149/2.1081613jesS144014431631

Redox stability and electrochemical study of nickel doped chromites as anodes for H-2/CH4-fueled solid oxide fuel cells

[EN] The influence of nickel and strontium incorporation in LaCrO3 on the crystalline structure, redox behavior and electrochemical performance by impedance spectroscopy using symmetrical cells has been studied. Namely, the La1-xSrxCr1-yNiyO3-delta (x = 0, 0.15: y = 0.05, 0.1, 0.2) system was investigated. Structural and redox evolution has been monitored by X-ray diffraction in oxidized and reduced samples. Reduced samples kept the initial perovskite structure although metallic nickel nanoparticles were detected on the perovskite grain surface by TEM analysis. The re-oxidized surface did not present nickel particles, suggesting the nickel re-incorporation into perovskite lattice coupled with cation diffusion. The perovskites were tested as SOFC anodes and the polarization resistance depended on the nickel stoichiometry and the reduction temperature. La0.85Sr0.15Cr0.9Ni0.1O3-delta reduced at 800 degrees C showed the lowest polarization resistance, both in hydrogen and methane. In fact this composition showed a 20% methane conversion at 900 degrees C for the methane steam reforming in a fixed bed reactor. Tolerance to redox cycling was proved electrochemically by in situ treatments of La0.85Sr0.15Cr0.9Ni0.1O3-delta electrode. Materials were further analyzed by TPR and XPS (in oxidized and reduced state) in order to identify the possible species involved in the electrocatalytic processes. (C) 2011 Elsevier B.V. All rights reserved.Authors thank funding by the Universidad Politecnica de Valencia (Grant FPI-UPV-2007-06), the Spanish Ministry for Science and Innovation (Project ENE2008-06302) and Generalitat Valenciana (Grant ACOMP2010/223). P. Concepcion has contributed to this work with the XPS measurements. N. Morlanes, S. Climent and M. Algarra are kindly acknowledged for the catalytic experiments.Vert Belenguer, VB.; Melo Faus, FV.; Navarrete Algaba, L.; Serra Alfaro, JM. (2012). Redox stability and electrochemical study of nickel doped chromites as anodes for H-2/CH4-fueled solid oxide fuel cells. Applied Catalysis B Environmental. 115:346-356. https://doi.org/10.1016/j.apcatb.2011.12.03334635611

Boosting methane partial oxidation on ceria through exsolution of robust Ru nanoparticles

[EN] Finding sustainable routes for the transformation of CO2 into fuels and added-value chemicals is key for mitigating greenhouse gas emission. In this respect, chemical-looping reforming coupled with CO2 splitting emerges as a promising technology to produce syngas, using waste or solar heat as an energy source. It relies on metal oxides that act as redox intermediates and, thus, the stability and catalytic activity of the oxides are crucial. For that purpose, ceria has been widely used due to its superior multicyclic stability and fast CO2 splitting kinetics. However, it also presents low capacity for oxygen exchange or supply compared with other oxides and slow methane partial oxidation kinetics, which is normally improved by cationic doping or catalytic surface activation via metal impregnation. The high temperatures (900 degrees C) required for these reactions lead to catalyst deactivation over time due to sintering of metallic clusters. In order to circumvent this issue, in this work we have utilized the exsolution method to create uniformly dispersed Ru nanoparticles (ca. 5 nm) that remain anchored to the cerium oxide backbone, guaranteeing its microstructural stability and catalytic activity over prolonged cycling. We provide evidence for metallic Ru exsolution and further demonstrate the outstanding benefits of exsolved nanoparticles in the partial oxidation of methane following a chemical-loop reforming scheme, especially in the temperature range in which industrial waste heat could be used as an energy source to drive the reaction. Remarkably, at 700 degrees C surface functionalization with exsolved Ru nanoparticles enables high CO selectivity (99% versus 62% for CeO2) and about 2 orders of magnitude faster H-2 production rates. The dispersion and size of the exsolved Ru nanoparticles were maintained after a durability test of 20 chemical loops at 900 degrees C, indicating their robustness. Overall, the results presented here point towards the unique characteristics of nanoparticle exsolution for preventing agglomeration, which could find application in other catalytic or electrochemical processes for target hydrocarbon production.AJC and MB would like to acknowledge the support of Juan de la Cierva fellowships by the Spanish Ministry of Science (grant numbers FJCI-2017-33967 and IJCI-2017-34110). We acknowledge the support of the Electronic Microscopy Service of the Universitat Politecnica de Valencia.Carrillo-Del Teso, AJ.; Navarrete Algaba, L.; Laqdiem-Marin, M.; Balaguer Ramirez, M.; Serra Alfaro, JM. (2021). Boosting methane partial oxidation on ceria through exsolution of robust Ru nanoparticles. Materials Advances. 2(9):2924-2934. https://doi.org/10.1039/d1ma00044f292429342

Hydrogen production via microwave-induced water splitting at low temperature

[EN] Hydrogen is a promising vector in the decarbonization of energy systems, but more efficient and scalable synthesis is required to enable its widespread deployment. Towards that aim, Serra et al. present a microwave-based approach that allows contactless water electrolysis that can be integrated with hydrocarbon production. Supplying global energy demand with CO2-free technologies is becoming feasible thanks to the rising affordability of renewable resources. Hydrogen is a promising vector in the decarbonization of energy systems, but more efficient and scalable synthesis is required to enable its widespread deployment. Here we report contactless H-2 production via water electrolysis mediated by the microwave-triggered redox activation of solid-state ionic materials at low temperatures (<250 degrees C). Water was reduced via reaction with non-equilibrium gadolinium-doped CeO2 that was previously in situ electrochemically deoxygenated by the sole application of microwaves. The microwave-driven reduction was identified by an instantaneous electrical conductivity rise and O-2 release. This process was cyclable, whereas H-2 yield and energy efficiency were material- and power-dependent. Deoxygenation of low-energy molecules (H2O or CO2) led to the formation of energy carriers and enabled CH4 production when integrated with a Sabatier reactor. This method could be extended to other reactions such as intensified hydrocarbons synthesis or oxidation.This work was supported by the Spanish Government (RTI2018-102161, SEV-2016-0683 and Juan de la Cierva grant IJCI-2017-34110). We thank the support of the Electronic Microscopy Service of the Universitat Politecnica de Valencia.Serra Alfaro, JM.; Borras-Morell, JF.; García-Baños, B.; Balaguer Ramirez, M.; Plaza González, PJ.; Santos-Blasco, J.; Catalán-Martínez, D.... (2020). Hydrogen production via microwave-induced water splitting at low temperature. 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Spontaneous Breathing in Early Acute Respiratory Distress Syndrome: Insights From the Large Observational Study to UNderstand the Global Impact of Severe Acute Respiratory FailurE Study

OBJECTIVES: To describe the characteristics and outcomes of patients with acute respiratory distress syndrome with or without spontaneous breathing and to investigate whether the effects of spontaneous breathing on outcome depend on acute respiratory distress syndrome severity. DESIGN: Planned secondary analysis of a prospective, observational, multicentre cohort study. SETTING: International sample of 459 ICUs from 50 countries. PATIENTS: Patients with acute respiratory distress syndrome and at least 2 days of invasive mechanical ventilation and available data for the mode of mechanical ventilation and respiratory rate for the 2 first days. INTERVENTIONS: Analysis of patients with and without spontaneous breathing, defined by the mode of mechanical ventilation and by actual respiratory rate compared with set respiratory rate during the first 48 hours of mechanical ventilation. MEASUREMENTS AND MAIN RESULTS: Spontaneous breathing was present in 67% of patients with mild acute respiratory distress syndrome, 58% of patients with moderate acute respiratory distress syndrome, and 46% of patients with severe acute respiratory distress syndrome. Patients with spontaneous breathing were older and had lower acute respiratory distress syndrome severity, Sequential Organ Failure Assessment scores, ICU and hospital mortality, and were less likely to be diagnosed with acute respiratory distress syndrome by clinicians. In adjusted analysis, spontaneous breathing during the first 2 days was not associated with an effect on ICU or hospital mortality (33% vs 37%; odds ratio, 1.18 [0.92-1.51]; p = 0.19 and 37% vs 41%; odds ratio, 1.18 [0.93-1.50]; p = 0.196, respectively ). Spontaneous breathing was associated with increased ventilator-free days (13 [0-22] vs 8 [0-20]; p = 0.014) and shorter duration of ICU stay (11 [6-20] vs 12 [7-22]; p = 0.04). CONCLUSIONS: Spontaneous breathing is common in patients with acute respiratory distress syndrome during the first 48 hours of mechanical ventilation. Spontaneous breathing is not associated with worse outcomes and may hasten liberation from the ventilator and from ICU. Although these results support the use of spontaneous breathing in patients with acute respiratory distress syndrome independent of acute respiratory distress syndrome severity, the use of controlled ventilation indicates a bias toward use in patients with higher disease severity. In addition, because the lack of reliable data on inspiratory effort in our study, prospective studies incorporating the magnitude of inspiratory effort and adjusting for all potential severity confounders are required

Identifying associations between diabetes and acute respiratory distress syndrome in patients with acute hypoxemic respiratory failure: an analysis of the LUNG SAFE database

Background: Diabetes mellitus is a common co-existing disease in the critically ill. Diabetes mellitus may reduce the risk of acute respiratory distress syndrome (ARDS), but data from previous studies are conflicting. The objective of this study was to evaluate associations between pre-existing diabetes mellitus and ARDS in critically ill patients with acute hypoxemic respiratory failure (AHRF). Methods: An ancillary analysis of a global, multi-centre prospective observational study (LUNG SAFE) was undertaken. LUNG SAFE evaluated all patients admitted to an intensive care unit (ICU) over a 4-week period, that required mechanical ventilation and met AHRF criteria. Patients who had their AHRF fully explained by cardiac failure were excluded. Important clinical characteristics were included in a stepwise selection approach (forward and backward selection combined with a significance level of 0.05) to identify a set of independent variables associated with having ARDS at any time, developing ARDS (defined as ARDS occurring after day 2 from meeting AHRF criteria) and with hospital mortality. Furthermore, propensity score analysis was undertaken to account for the differences in baseline characteristics between patients with and without diabetes mellitus, and the association between diabetes mellitus and outcomes of interest was assessed on matched samples. Results: Of the 4107 patients with AHRF included in this study, 3022 (73.6%) patients fulfilled ARDS criteria at admission or developed ARDS during their ICU stay. Diabetes mellitus was a pre-existing co-morbidity in 913 patients (22.2% of patients with AHRF). In multivariable analysis, there was no association between diabetes mellitus and having ARDS (OR 0.93 (0.78-1.11); p = 0.39), developing ARDS late (OR 0.79 (0.54-1.15); p = 0.22), or hospital mortality in patients with ARDS (1.15 (0.93-1.42); p = 0.19). In a matched sample of patients, there was no association between diabetes mellitus and outcomes of interest. Conclusions: In a large, global observational study of patients with AHRF, no association was found between diabetes mellitus and having ARDS, developing ARDS, or outcomes from ARDS. Trial registration: NCT02010073. Registered on 12 December 2013