Laura Navarrete

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

New composite cathodes for proton conducting solid oxide fuel cells (PC-SOFCs) based on the novel La5.5WO12−δ (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−δ (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 °C) have been studied. Electrochemical impedance spectroscopy (EIS) analysis has been carried out in the temperature range 700–900 °C under moist (2.5% H2O) atmospheres. Different oxygen partial pressures (pO2) 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.

Boosting the oxygen reduction reaction mechanisms in IT-SOFC cathodes by catalytic functionalization

A robust LSM-GDC composite was used as a backbone electrode for the infiltration of different catalysts, dispersed as oxide nanoparticles after firing. Catalyst candidates were screened using symmetric cells supported on the GDC electrolyte. Among the tested catalysts, praseodymium infiltration exhibited an outstanding and highly stable promotion effect of the oxygen reduction reaction. Impedance spectroscopy modelling provided insight into the nature of the distinct mechanisms limiting the cathode performance. The Pr-promotion in cathodes resulted in a fivefold rise in the power density peak when tested on a fully assembled anode-supported fuel cell.

Enhancing oxygen permeation through Fe2NiO4–Ce0.8Tb0.2O2−δ composite membranes using porous layers activated with Pr6O11 nanoparticles

Fe2NiO4–Ce0.8Tb0.2O2−δ (NFO–CTO) composite membranes are of interest to separate oxygen from air. In this study, we investigate the influence of the catalytic activation of NFO–CTO membranes on the oxygen permeation rate. Specifically, the effect of activating porous NFO–CTO layers –coated on both sides of the dense NFO–CTO membrane – with Pr6O11 nanoparticles is studied. Measurements in the temperature range 850–700 °C revealed a 2–4 fold increase in the oxygen flux after coating a 30 μm-thick porous NFO–CTO layer on both membrane sides, and a 6–12 fold increase relative to the bare membrane after activating the porous layers coated on both sides of the membrane with Pr6O11 nanoparticles. No degradation of the oxygen fluxes was found in CO2-containing atmospheres. Pulse isotopic exchange measurements confirmed an increase in the oxygen surface exchange rate of more than one order of magnitude after dispersion of Pr6O11 nanoparticles on the surface of NFO–CTO composite powders. Electrochemical impedance spectroscopy measurements on symmetrical cells, using Gd-doped ceria (CGO) as the electrolyte and Pr6O11-activated NFO–CTO electrodes, showed a 10-fold decrease in the polarization resistance compared to non-infiltrated electrodes in air. Modification of porous layers by activation with Pr6O11 nanoparticles is considered a viable route to enhance the oxygen fluxes across composite membranes.

SnO 2 and Ce modified SnO 2 mesostructured for selective ethanol detection

SnO2 and Ce modified SnO2 mesoarchitectured have been prepared using an ionic surfactant (CTAB) as template for sensing applications. The procedure involves a versatile route based on hydrothermal treatment under autogenous pressure for obtaining mesoarchitectures built from nanoparticles. The structural, textural and morphological features of the resultant powders were investigated by scanning electron microscopy (SEM), while the surface chemistry was closely monitored by X-ray photoelectron spectroscopy (XPS). H2, CO and C2H6O responses are studied.