(365g) Nanostructuring, Oxygen Anion Diffusion Study and Electrochemical Performance of Double Perovskite Electrode for SOFC

The state of the
art requires the synthesis of nanostructured materials to be used as
electrodes, which will show improved electro-catalytic activity and bulk
transport, thus in-turn providing better electrochemical performance. Chemical
synthesis methods show limitations in obtaining reduced particle sizes. For
example on adopting a chemical synthesis method an average particle size of 40
nm was obtained of GaBaCo₂O_5+d (GBCO). Herein an
attempt is made to reduce the particle size further by using a relatively green
and novel top-down bio-milling process. The GBCO powder was subjected to a
fungus, Sacchromyces cerevisiae, which was cultured in 250 mL YPD medium
for 96h at 301K. We report the reduction in particle size of phase pure (fig1a)
GBCO to a size lesser than 20 nm as observed using HR-TEM. Thin-film of La_0.6Sr_0.4Co_0.2Fe_0.8O_3-d
(LSCF) electrodes (thickness ~500 nm), were fabricated using a spray deposition
method. In order to test the electro-catalytic performance of the GBCO
nanoparticles, symmetric cells of GBCO on gadolin doped ceria (GDC) electrolyte
were fabricated and electrochemical performance measured in area specific
resistance was compared to the chemically synthesized GBCO (fig1b).Molecular
dynamics simulations were performed to study the transport of oxygen anion [1]
in anisotropic GBCO. The diffusivity of the GBCO was observed to be thermally
activated with an activation energy (E_a) of 50.8 kJ/mol (fig1d).The
diffusion coefficient was calculated to be of the value of 5 x 10^-8
at 873K in a-b plan which was observed to be higher by an order of
magnitude in comparison to the diffusion c axis (3.33 x 10^-9
cm² s^-1) (fig1c). Similarly, the effect of Fe dopant on
diffusivity at B site was measured in case of GdBa_0.5Sr_0.5Co_2-xFe_xO_5.5
structure for x = 0 to 1. Where, it was concluded that the oxygen anion
diffusion was maximum in case of 50% Fe substituted composition as shown in
Table1

Table 1: Oxygen anion diffusion coefficient of double
perovskite materials

Figure 1: a)XRD and HR-TEM image of biomilled
nanoparticle, b) Nyquist plot of GBCO

nanoparticle doped electrode, c) oxygen density profile
where, blue represent Ba and yellow

and green represent Co and Gd atoms respectively and d)
Arrhenius plot of oxygen diffusion

calculated from MD.