SrFeO3−δ has
been earlier reported
to exhibit
a large area-specific resistance even though it possesses high mixed
ionic–electronic conductivity both in oxidizing and reducing
conditions. The present study clarifies this aspect and investigates
the defect chemistry and electrochemical performance correlations
in SrFeO3−δ
for the possible
use as a symmetric electrode in solid oxide fuel cells. A conventional
solid-state reaction method is adopted for powder synthesis. Structural
characterization indicates an orthorhombic perovskite phase formation
with a δ of 0.21. High dc electrical conductivities
of ∼114.9 and 0.26 S·cm–1 are observed
at 800 °C in air and reducing conditions, respectively. The area-specific
resistance (ASR) for the SrFeO3−δ
electrode is measured in a symmetrical half-cell configuration
under various gas environments. At 800 °C, SrFeO3−δ
offered low ASRs of 0.082, 0.055, and 0.122
Ω·cm2 in air, oxygen, and 3% H2O/H2, respectively. Although the ASR possesses excellent temporal
stability in an oxidizing atmosphere, it increases to 0.42 Ω·cm2 after 100 h in reducing conditions owing to the brownmillerite
phase formation. The redox cycling performance is also affected with
the ASR rising from 0.13 to 0.24 Ω·cm2 at 800
°C in 3% H2O/H2 after 20 cycles. A maximum
power density of 202 mW·cm−2 is achieved from
the electrolyte-supported symmetric single cell based on the SrFeO3−δ
electrodes at 800 °C.
The results demonstrate the viability of using a SrFeO3−δ
-based electrode for symmetrical solid oxide
fuel cells.
The electrochemical performance of porous composites of Gd 0.1 Ce 0.9 O 2−δ /SrMg 0.1 Mo 0.9 O 3−δ is investigated for the anode application under a typical fuel environment of solid oxide fuel cells (SOFCs). Nanosized powder of SrMg 0.1 Mo 0.9 O 3−δ possessing a cubic perovskite phase is synthesized using the solution-combustion method. Composites having the composition of xGd 0.1 Ce 0.9 O 2−δ /SrMg 0.1 Mo 0.9 O 3−δ (where x is a weight fraction of Gd 0.1 Ce 0.9 O 2− δ ranging from 0.5 to 0.8) are prepared using a traditional mixing method. At 850 °C, the DC electrical conductivity of SrMg 0.1 Mo 0.9 O 3−δ under moist 20% H 2 /N 2 is 617 S•cm −1 which declines to ∼105 S•cm −1 for 0.6Gd 0.1 Ce 0.9 O 2−δ /SrMg 0.1 Mo 0.9 O 3−δ . Symmetric cells are fabricated using dense disks of yttriastabilized zirconia as an electrolyte with a thin Gd 0.1 Ce 0.9 O 2−δ buffer layer coated on both faces. An optimized slurry of the composite electrode is blade-coated on the dense buffer layer and subsequently sintered at 950 °C in air. Scanning electron microscopy reveals a porous microstructure with an electrode layer thickness of ∼14 μm. A single-phase SrMg 0.1 Mo 0.9 O 3−δ electrode exhibits an area-specific resistance of 0.28 Ω•cm 2 , which is less than 6 times the value offered by undoped SrMoO 3 at 800 °C in 3% H 2 O/H 2 . The optimum Gd 0.1 Ce 0.9 O 2−δ addition (x = 0.7) to SrMg 0.1 Mo 0.9 O 3−δ resulted in a significantly low area-specific resistance of 0.09 Ω•cm 2 at 800 °C. The performance of the optimized electrode composite is also evaluated by modifying the microstructure of the Gd 0.1 Ce 0.9 O 2−δ buffer layer. Interestingly, the symmetrical cell with a porous buffer layer further reduces the electrode areaspecific resistance to 0.065 Ω•cm 2 . The observed results are ascribed to the penetration of electrocatalyst SrMg 0.1 Mo 0.9 O 3−δ particles inside the porous buffer layer during the blade-coating. This possibly extends the triple-phase boundary length and facilitates the charge-transfer reaction. The electrochemical performance attained in the present study is far superior to the other Ni-free ceramic anodes reported earlier, which highlights the promise of 0.7Gd 0.1 Ce 0.9 O 2−δ /SrMg 0.1 Mo 0.9 O 3−δ for the SOFC anode.
In this paper, we propose analytical modeling of double gate (DG) tunnel field effect transistor (TFET) which is derived by using Evanescent-mode analysis approach. This approach considers the channel potential as the sum of a long channel potential and a short channel perturbation along with the whole structure rather than just the Si/SiO 2 interface or the channel centre. Due to this, the characteristic length lambda (λ) does not depend on the transverse position within the channel. Analytical potential modeling of DG-TFET along with evaluation of electric field and drain current has been carried out. It has also been shown in the results that the proposed model has better channel potential and tunnel current than single-gate SOI TFET.
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