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Nanoionics and Nanocatalysts: Conformal Mesoporous Surface Scaffold for Cathode of Solid Oxide Fuel Cells

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ABSTRACT

Nanoionics has become increasingly important in devices and systems related to energy conversion and storage. Nevertheless, nanoionics and nanostructured electrodes development has been challenging for solid oxide fuel cells (SOFCs) owing to many reasons including poor stability of the nanocrystals during fabrication of SOFCs at elevated temperatures. In this study, a conformal mesoporous ZrO2 nanoionic network was formed on the surface of La1−xSrxMnO3/yttria-stabilized zirconia (LSM/YSZ) cathode backbone using Atomic Layer Deposition (ALD) and thermal treatment. The surface layer nanoionic network possesses open mesopores for gas penetration, and features a high density of grain boundaries for enhanced ion-transport. The mesoporous nanoionic network is remarkably stable and retains the same morphology after electrochemical operation at high temperatures of 650–800 °C for 400 hours. The stable mesoporous ZrO2 nanoionic network is further utilized to anchor catalytic Pt nanocrystals and create a nanocomposite that is stable at elevated temperatures. The power density of the ALD modified and inherently functional commercial cells exhibited enhancement by a factor of 1.5–1.7 operated at 0.8 V at 750 °C.

No MeSH data available.


A two-phase coating of superjacent ZrO2 layer subjacent Pt (cell #6).(a) As-deposited state of the ~3 nm Pt layer and the 40 nm amorphous ZrOx layer. (b) Conformal amorphous ZrOx layer turned into a continuous crystalline ZrO2 layer covering the entire backbone of the cathode.
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f3: A two-phase coating of superjacent ZrO2 layer subjacent Pt (cell #6).(a) As-deposited state of the ~3 nm Pt layer and the 40 nm amorphous ZrOx layer. (b) Conformal amorphous ZrOx layer turned into a continuous crystalline ZrO2 layer covering the entire backbone of the cathode.

Mentions: The unique architectural and crystalline character of each as-deposited ALD layer (amorphous ZrOx or crystalline Pt) offers an opportunity to engineer architecture by leveraging the thermodynamically controlled characteristics of the constituent phases. Specially, the strategy is to pin Pt particles to the cathode surface using stable ZrO2 nanoionic network, therefore to retain the highly active electrocatalytic structure even when the system is subjected to aggressive driving potentials at elevated temperatures. One approach successfully applied a two-phase coating of amorphous ZrOx on a backbone-deposited Pt layer composed of discrete ~3 nm Pt crystallites. As shown in Fig. 3a (from cell #6) the ZrOx coating layer is ~40 nm thick, and pins the Pt particles to the backbone surface. The as-deposited ZrOx is amorphous and homogeneous, therefore the nanovoids (~1–3 nm in dimension, as shown in Supplementary Figure 2a) between neighboring Pt crystals were filled with amorphous ZrOx. This layered structure, with superjacent amorphous ZrOx and subjacent crystalline Pt, was subjected to heat-treatment before cell operation. As shown in Fig. 3b (and enlarged view in Supplementary Figure 3), the amorphous ZrOx conformal layer transformed into a crystalline ZrO2 layer covering the entire backbone of the cathode. The layered ZrO2 architecture contains mesopores that preserve the gas pathway and disrupt agglomeration of the discrete Pt particles of ~10 nm that were fully pinned to the backbone surface. Remarkably, the engineered architecture depicted in Fig. 3b results in a performance enhancement of commercial button cells by a factor of 1.6 at 0.8 V (in Table 1).


Nanoionics and Nanocatalysts: Conformal Mesoporous Surface Scaffold for Cathode of Solid Oxide Fuel Cells
A two-phase coating of superjacent ZrO2 layer subjacent Pt (cell #6).(a) As-deposited state of the ~3 nm Pt layer and the 40 nm amorphous ZrOx layer. (b) Conformal amorphous ZrOx layer turned into a continuous crystalline ZrO2 layer covering the entire backbone of the cathode.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5015090&req=5

f3: A two-phase coating of superjacent ZrO2 layer subjacent Pt (cell #6).(a) As-deposited state of the ~3 nm Pt layer and the 40 nm amorphous ZrOx layer. (b) Conformal amorphous ZrOx layer turned into a continuous crystalline ZrO2 layer covering the entire backbone of the cathode.
Mentions: The unique architectural and crystalline character of each as-deposited ALD layer (amorphous ZrOx or crystalline Pt) offers an opportunity to engineer architecture by leveraging the thermodynamically controlled characteristics of the constituent phases. Specially, the strategy is to pin Pt particles to the cathode surface using stable ZrO2 nanoionic network, therefore to retain the highly active electrocatalytic structure even when the system is subjected to aggressive driving potentials at elevated temperatures. One approach successfully applied a two-phase coating of amorphous ZrOx on a backbone-deposited Pt layer composed of discrete ~3 nm Pt crystallites. As shown in Fig. 3a (from cell #6) the ZrOx coating layer is ~40 nm thick, and pins the Pt particles to the backbone surface. The as-deposited ZrOx is amorphous and homogeneous, therefore the nanovoids (~1–3 nm in dimension, as shown in Supplementary Figure 2a) between neighboring Pt crystals were filled with amorphous ZrOx. This layered structure, with superjacent amorphous ZrOx and subjacent crystalline Pt, was subjected to heat-treatment before cell operation. As shown in Fig. 3b (and enlarged view in Supplementary Figure 3), the amorphous ZrOx conformal layer transformed into a crystalline ZrO2 layer covering the entire backbone of the cathode. The layered ZrO2 architecture contains mesopores that preserve the gas pathway and disrupt agglomeration of the discrete Pt particles of ~10 nm that were fully pinned to the backbone surface. Remarkably, the engineered architecture depicted in Fig. 3b results in a performance enhancement of commercial button cells by a factor of 1.6 at 0.8 V (in Table 1).

View Article: PubMed Central - PubMed

ABSTRACT

Nanoionics has become increasingly important in devices and systems related to energy conversion and storage. Nevertheless, nanoionics and nanostructured electrodes development has been challenging for solid oxide fuel cells (SOFCs) owing to many reasons including poor stability of the nanocrystals during fabrication of SOFCs at elevated temperatures. In this study, a conformal mesoporous ZrO2 nanoionic network was formed on the surface of La1−xSrxMnO3/yttria-stabilized zirconia (LSM/YSZ) cathode backbone using Atomic Layer Deposition (ALD) and thermal treatment. The surface layer nanoionic network possesses open mesopores for gas penetration, and features a high density of grain boundaries for enhanced ion-transport. The mesoporous nanoionic network is remarkably stable and retains the same morphology after electrochemical operation at high temperatures of 650–800 °C for 400 hours. The stable mesoporous ZrO2 nanoionic network is further utilized to anchor catalytic Pt nanocrystals and create a nanocomposite that is stable at elevated temperatures. The power density of the ALD modified and inherently functional commercial cells exhibited enhancement by a factor of 1.5–1.7 operated at 0.8 V at 750 °C.

No MeSH data available.