Growth of finely dispersed nanocatalysts by exsolution of metal nanoparticles from perovskite oxides under reducing conditions at elevated temperature is a promising approach of producing highly active catalytic materials. An alternative method of exsolution using an applied potential has been recently shown to potentially accelerate the exsolution process of nanoparticles that can be achieved in minutes rather than the hours required in chemical reduction. In the present study, we investigate exsolution of nanoparticles from perovskite oxides of La 0.43 Ca 0.37 Ni 0.06 Ti 0.94 O 3-γ (LCTNi) and La 0.43 Ca 0.37 Ni 0.03 Fe 0.03 Ti 0.94 O 3-γ (LCTNi-Fe) under applied potentials in carbon dioxide atmosphere. The impedance spectra of single cells measured before and after electrochemical poling at varying voltages showed that the onset of exsolution process occurred at 2 V of potential reduction. An average particle size of the exsolved nanoparticles observed after testing using a scanning electron microscopy was about 30-100 nm. The cells with the reduced electrodes exhibited desirable electrochemical performances not only in pure carbon dioxide (current density of 0.37 A cm −2 for LCTNi and 0.48 A cm −2 for LCTNi-Fe at 1.5 V) but also in dry hydrogen (0.36 W cm −2 for LCTNi and 0.43 W cm −2 for LCTNi-Fe).
Oxygen incorporation for the oxygen reduction reaction at a porous mixed-conducting LaSrCoO3 (LSC) electrode was experimentally investigated using technique of oxygen isotope (18O) labelling coupled with subsequent quenching and secondary ion mass spectrometer (SIMS) imaging. The isotopic oxygen exchange experiments of porous LSC cathode were conducted under current density conditions of 0 (OCV), 0.05 and 0.24 A cm−2. Distribution images of incorporated 18O inside solid oxide microstructures and analyzed concentration profiles along the LSC cathode thickness are presented. The 18O distribution image and concentration profile under an applied current density clearly reflect extension of active reaction zone over surface area of LSC, as well as distribution of oxygen chemical potential in the porous LSC cathode. The non-uniform profiles under influence of applied currents revealed that oxygen chemical potential distribution in porous mixed-conducting LSC cathode strongly depends on an applied current density. The analyzed profiles also showed a significant interfacial barrier to the oxygen diffusion across the interface between the GDC interlayer and the YSZ electrolyte due to the unfavorable diffusion of Sr from the LSC to the GDC/YSZ interface. The present results provide the first experimental evidence of oxygen chemical potential distribution in the porous mixed-conducting LSC cathode.
This study aims to investigate reaction pathways of carbon deposition on the Ni/YSZ anode of SOFC. Experimental study showed that the carbon was deposited through CH 4 decomposition on Ni particles. It was also implied that the deposited carbon itself catalyzed CH 4 decomposition. The carbon deposition steadily progressed after Ni particles were covered by the carbon. The carbon deposition led to destructing the microstructure of Ni/YSZ anode to the extent that the recovery was difficult. The detailed chemical kinetics analysis was also performed to investigate the carbon deposition on the Ni surface. The surface coverage of carbon significantly decreased by adding steam. From the sensitivity analysis, it was shown that the enhancement of the carbon oxidation and H 2 O adsorption on the Ni surface were effective to inhibit carbon deposition on the anode of the SOFC.
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