INVESTIGADORES
SOLDATI Analia Leticia
capítulos de libros
Título:
Electrode/electrolyte Interface Characterization in Solid Oxide Fuel Cells
Autor/es:
SOLDATI, ANALIA L.; BAQUÉ, LAURA; TROIANI, HORACIO; SERQUIS, ADRIANA C.
Libro:
Hydrogen Energy
Editorial:
Intech Open Minds
Referencias:
Lugar: Rijeka; Año: 2012; p. 280 - 304
Resumen:
Fuel cells (FC)
have reached a recognized place within the potencially efficient devices to
convert chemical energy into electricity. First developed by William Grove in
1835, FC had a profound impact in the aerospatial industry and more
rencently gained special attention for wider applications, because they are
considered as environmental friendly devices. Indeed, when Hydrogen is used as
fuel, the device produces only water as residue, with no impact on the
undesidered CO2 emissions.
Between the
different FC types, those based of solid oxides (SOFC) found a place in mobile
and stationary applications. These cells are operated between high (1000ºC) and intermediate (700ºC) temperature ranges and
the principal characteristic is that their fundamental parts consist on ceramic
materials. The reduction of the oxygen molecule takes place in the cathode,
liberating two electrons; afterwards the O2- ion travels through the
electrolyte to the anode material, where it oxidizes the hydrogen molecule,
releasing a water molecule and closing the circuit.
Good gas
permeability, high electron (and oxygen ion) conductivities and low
inter-material reactivities are a material requirement for a sucessfull operation,
independent of the electrode/electrolyte nature. On one hand, the combination
of mixed conductors such as rare earth doped perovskites with Ceria or Ytria
are considered good electrode/electrolyte choices . On the other hand, reducing
cathode particle size has shown to be a good alternative to decrease the
cathode area specific resistance (ASR) and improve the general efficiency of
the device.
Other important point to optimize is
the assembly electrode/electrolyte interface., In situ
observations of microstructure, morphology and composition at the atomic scale
at the interfacial area are needed in order to understand the phenomena that
occur in this region. In this chapter we present a review of current techniques
that can be used to select and study this challenging region, based on
literature data and our own research in that field.
One of the
most versatile tools to prepare samples of selected areas for in situ
microscopy and spectroscopy analyses is the Focused Ion Beam (FIB). With help
of an electron microscope a desired area can be selected with micrometric
precision and a Ga-ion beam is used to extract a thin sample of the bulk. This
foil, with only some nm thickness, can be after analyzed with scanning (SEM) or
transmission (TEM) microscopes and related techniques. Z-contrast, Energy
dispersive spectroscopy (EDS) and Energy Loss Spectroscopy (EELS) are commonly
choices for composition analyses. Electron Backscatter Diffraction (EBSD) is
used for texture analysis. FIB-SEM micro-tomography allows finding structure
related parameters as pore concentration, tortuosity or contact area. We will
present results of these kinds of analyses in two cathode/electrolyte
interfaces of intermediate temperature (IT-) cells. The two assemblies studied
comprise a nanostructured cathode of La0.4Sr0.6Co0.8Fe0.2O3-d (LSCF) in the first case and La2NiO4+d (LNO) in the second case, deposited over Ce0.9Gd0.1O2-d (CGO) electrolytes by spin coating. The
LSCF/CGO half cell presents a semi-coherent interface at the atomic level, with
very high percentage of contact area. These structural properties contribute to
the good conductivity and lower ASR values measured in this assembly. Besides,
the LNO/CGO interface shows high interfacial reactivity, with zones of change
of composition, formation of other phases and interfacial porosity. In this
latter assembly, structural, composition and morphological observations could
be related to the low general efficiency and high degradation rates under
operation conditions.