Person:
García Alvarado, Flaviano

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First Name
Flaviano
Last Name
García Alvarado
URI
https://hdl.handle.net/20.500.14352/83095
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Químicas
Department
Area
Química Inorgánica
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2017 - 20192
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Author: Amador, Ulises ×

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    Novel perovskite materials for thermal water splitting at moderate temperature
    (Chemsuschem, 2019) Azcondo, M. Teresa; Orfila, María; Marugán, Javier; Sanz Martín, Raúl; Muñoz Noval, Álvaro; Salas Colera, Eduardo; Ritter, Clemens; García Alvarado, Flaviano; Amador, Ulises
    Materials with the formula Sr_2CoNb_1-xTi_xO_(6-delta) (x=1.00, 0.70; delta=number of oxygen vacancies) present a cubic perovskite-like structure. They are easily and reversibly reduced in N_2 or Ar and re-oxidized in air upon heating. Oxidation by water (wet N_2), involving splitting of water at a temperature as low as 700 ºC, produces hydrogen. Both compounds displayed outstanding H_2 production in the first thermochemical cycle, the Sr_2CoNb_(0.30)Ti_(0.70)O_(6-delta) material retaining its outstanding performance upon cycling, whereas the hydrogen yield of the x=1 oxide showed a continuous decay. The retention of the materials' ability to promote water splitting correlated with their structural, chemical, and redox reversibility upon cycling. On reduction/oxidation, Co ions reversibly changed their oxidation state to compensate the release/recovery of oxygen in both compounds. However, in Sr_2CoTiO_(6-delta), two phases with different oxygen contents segregated, whereas in Sr_2CoNb_(0.30)Ti_(0.70)O_(6-delta) this effect was not evident. Therefore, this latter material displayed a hydrogen production as high as 410 mu molH_2/g_(perovskite) after eight thermochemical cycles at 700 ºC, which is among the highest ever reported, making this perovskite a promising candidate for thermosolar water splitting in real devices.
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    Defect chemistry, electrical properties and evaluation of new oxides Sr2CoNb1-xTixO6-δ (0≤x≤1) as cathode materials for Solid Oxide Fuel Cells
    (ChemSusChem, 2017) Azcondo, Teresa; Yuste, Mercedes; Pérez-Flores, Juan Carlos; Muñoz Gil, Daniel; García Martín, Susana; Muñoz Noval, Álvaro; Puente Orench, Inés; García Alvarado, Flaviano; Amador, Ulises
    The perovskite series Sr2CoNb1-xTixO6-δ (0≤x≤1) is investigated in the full compositional range to assess its potential as cathode material for solid state fuel cell (SOFC). The variation of transport properties and thus, the area specific resistances (ASR) are explained by a detailed investigation of the defect chemistry. Increasing titanium content from x=0 to x=1 produces both oxidation of Co3+ to Co4+ (from 0% up to 40%) and oxygen vacancies (from 6.0 to 5.7 oxygen atom/formula unit) though each charge compensation mechanism predominates in different compositional ranges. Neutron diffraction reveals that samples with high Ti-contents lose a significant amount of oxygen on heating above 600K. Oxygen is partially recovered on cooling since the oxygen release and uptake show noticeably different kinetics. The complex defect chemistry of these compounds, together with the compositional changes upon heating-cooling cycles and atmospheres produce, a complicated behaviour of electrical conductivity. Cathodes containing Sr2CoTiO6-δ display low ASR values, 0,13 Ωcm2 at 973 K, comparable to those of the best compounds reported so far, being a very promising cathode material for SOFC.