135 research outputs found
Dopants and defects in proton-conducting perovskites
Many doped perovskites show high proton conductivity at intermediate to high temperatures (500-
900 °C), which has opened possibilities for many prospected applications in energy conversion (fuel
cells), and electrochemical devices. In a doped perovskite, e.g. BaCe1-xYxO3-y, oxygen vacancies
are created by charge compensation, and can eventually react with air moisture to form structural
protonic defects. The sluggish nature of the proton, which is practically invisible to most structural
analyses, and poses enormous problems to quantum chemistry, has surely contributed to slow down
the progress in the understanding of these materials: in fact, the conduction dynamics and its
interplay with structure are still matter of debate. The kind of trivalent dopant and its size, and the
doping level, have all been found to critically influence the conductivity: to date, however, no
comprehensive model was developed, and no clear explanations exist between the chemical and
dynamical properties.
Here we present results collected in several EXAFS experiments on doped BaCeO3 and
BaZrO3 spanning three years, on the Ba site, Ce site, and the dopant (yttrium, gadolinium,
indium: the ionic sizes of these are respectively equal, larger and smaller than Ce4+) site. The
local structures up to about 6 AĚ around each site are solved with state-of-the-art techniques
employing both the GNXAS and FEFF approaches, revealing unique features and
demonstrating that in this case the conventional diffraction techniques are not suited to
unravel the complexity of doped crystals. In particular, the attention will be drawn on the
local deviations from Vegardâs law, the local expansion/contraction as a function of hydration
degree, the interplay between dopant and defects, and the chemical compatibility (Pearson
absolute hardness) instead of ionic size matching. The EXAFS results are correlated with
complementary information about the dynamics of protons and other defects (IR and neutron
vibrational spectroscopy, QENS, ionic and electronic conductivity measurements)
Thermo-electrochemical production of compressed hydrogen from methane with near-zero energy loss
[EN] Conventional production of hydrogen requires large industrial plants to minimize energy losses and capital costs associated with steam reforming, water-gas shift, product separation and compression. Here we present a protonic membrane reformer (PMR) that produces high-purity hydrogen from steam methane reforming in a single-stage process with near-zero energy loss. We use a BaZrO3-based proton-conducting electrolyte deposited as a dense film on a porous Ni composite electrode with dual function as a reforming catalyst. At 800 degrees C, we achieve full methane conversion by removing 99% of the formed hydrogen, which is simultaneously compressed electrochemically up to 50 bar. A thermally balanced operation regime is achieved by coupling several thermo-chemical processes. Modelling of a small-scale (10 kg H-2 day-1) hydrogen plant reveals an overall energy efficiency of >87%. The results suggest that future declining electricity prices could make PMRs a competitive alternative for industrial-scale hydrogen plants integrating CO2 capture.This work was supported by the Research Council of Norway (grant 256264) and the Spanish Government (SEV-2016-0683 grant).Malerød-Fjeld, H.; Clark, D.; Yuste Tirados, I.; ZanĂłn GonzĂĄlez, R.; CatalĂĄn-MartĂnez, D.; Beeaff, D.; HernĂĄndez Morejudo, S.... (2017). Thermo-electrochemical production of compressed hydrogen from methane with near-zero energy loss. Nature Energy. 2(12):923-931. https://doi.org/10.1038/s41560-017-0029-4S923931212Morejudo, S. H. et al. Direct conversion of methane to aromatics in a catalytic co-ionic membrane reactor. Science 353, 563â566 (2016).Chu, S. & Majumdar, A. Opportunities and challenges for a sustainable energy future. Nature 488, 294â303 (2012).Logan, B. E. & Elimelech, M. Membrane-based processes for sustainable power generation using water. Nature 488, 313â319 (2012).Rostrup-Nielsen, J. 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Irreversibility of proton conductivity of Nafion and NafionâTitania composites at high relative humidity
First-principles molecular dynamics simulations of proton diffusion in cubic BaZrO 3 perovskite under strain conditions
The effects of water on the morphology and the swelling behavior of sulfonated poly(ether ether ketone) films
Electrophysical properties of nanoporous cerium dioxideâwater system
The impedance of nanoporous cerium dioxide with adsorbed water is investigated in the frequency range 103â104 Hz at temperatures near the waterâice phase transition. Here we show that the manifestation of impedance peculiarities at phase transition is caused by the dielectric constant of the matrix
Preparation and Characterization of an Eco-Friendly Polymer Electrolyte Membrane (PEM) Based in a Blend of Sulphonated Poly(Vinyl Alcohol)/ Chitosan Mechanically Stabilised by Nylon 6,6
Optical anisotropy, molecular orientations, and internal stresses in thin sulfonated poly(ether ether ketone) films
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