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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.

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Cell performance upon operation at 750 °C and nanostructure.(a) Performance of the baseline cell (cell #1) and cell #3 with 40 nm ZrO2. (b) Nyquist plot of cell #1 (the baseline cell, in red squares), cell #2 (20 nm ZrO2, in green circles), cell #3 (40 nm ZrO2, in magenta diamonds) and cell #4 (60 nm ZrO2, in blue pentagons), showing the significant decrease of Rs and Rtotal of the coated cells except Rs of cell #2. (c) Bode plot of cell #1, cell #2, cell #3 and cell #4 showing the trend of the intermediate-frequency arc in the range of 1–100 Hz. (d) Cross section TEM image shows the ~40 nm porous nano ZrO2 layer on the LSM/YSZ backbone. The insert plan-view image shows that the ZrO2 surface layer is nano-grained and porous. The blue-arrowed areas are mesopores randomly distributed through the entire ZrO2 surface layer. (e), TEM image shows no significant change of ALD ZrO2 surface layer after 400 hours operation.
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f1: Cell performance upon operation at 750 °C and nanostructure.(a) Performance of the baseline cell (cell #1) and cell #3 with 40 nm ZrO2. (b) Nyquist plot of cell #1 (the baseline cell, in red squares), cell #2 (20 nm ZrO2, in green circles), cell #3 (40 nm ZrO2, in magenta diamonds) and cell #4 (60 nm ZrO2, in blue pentagons), showing the significant decrease of Rs and Rtotal of the coated cells except Rs of cell #2. (c) Bode plot of cell #1, cell #2, cell #3 and cell #4 showing the trend of the intermediate-frequency arc in the range of 1–100 Hz. (d) Cross section TEM image shows the ~40 nm porous nano ZrO2 layer on the LSM/YSZ backbone. The insert plan-view image shows that the ZrO2 surface layer is nano-grained and porous. The blue-arrowed areas are mesopores randomly distributed through the entire ZrO2 surface layer. (e), TEM image shows no significant change of ALD ZrO2 surface layer after 400 hours operation.

Mentions: In the present work, a total of seven cells with six of the cells having differently engineered surface architectures on the cathode were investigated. All the cells and their corresponding performances are listed in Table 1. For three cells (#2, #3 and #4), a pure ZrOx layer was deposited by ALD onto the LSM/YSZ cathode backbone of commercial anode-supported SOFCs. The as-deposited state of the ZrOx layer is amorphous and conformal on the cathode backbone. By controlling the ALD processing cycles, a uniform layer with thickness of 20, 40 and 60 nm was deposited on the cathode of three cells, respectively. All cells were subjected to heat treatment to crystallize the ZrO2 structure before cell operation. Subsequently, an electrochemical test was performed at 750 °C in H2 and air for anode and cathode, respectively. In comparison with the baseline cell (cell #1), power density increases were observed for all three cells (in Table 1). In particular, as shown in Fig. 1a–c, a large power density increase by a factor of 1.5, accompanied by the simultaneous large decrease of both series resistance Rs and polarization resistance Rp was observed for cell #3 with 40 nm ZrO2 coating layer.


Nanoionics and Nanocatalysts: Conformal Mesoporous Surface Scaffold for Cathode of Solid Oxide Fuel Cells
Cell performance upon operation at 750 °C and nanostructure.(a) Performance of the baseline cell (cell #1) and cell #3 with 40 nm ZrO2. (b) Nyquist plot of cell #1 (the baseline cell, in red squares), cell #2 (20 nm ZrO2, in green circles), cell #3 (40 nm ZrO2, in magenta diamonds) and cell #4 (60 nm ZrO2, in blue pentagons), showing the significant decrease of Rs and Rtotal of the coated cells except Rs of cell #2. (c) Bode plot of cell #1, cell #2, cell #3 and cell #4 showing the trend of the intermediate-frequency arc in the range of 1–100 Hz. (d) Cross section TEM image shows the ~40 nm porous nano ZrO2 layer on the LSM/YSZ backbone. The insert plan-view image shows that the ZrO2 surface layer is nano-grained and porous. The blue-arrowed areas are mesopores randomly distributed through the entire ZrO2 surface layer. (e), TEM image shows no significant change of ALD ZrO2 surface layer after 400 hours operation.
© Copyright Policy - open-access
Related In: Results  -  Collection

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f1: Cell performance upon operation at 750 °C and nanostructure.(a) Performance of the baseline cell (cell #1) and cell #3 with 40 nm ZrO2. (b) Nyquist plot of cell #1 (the baseline cell, in red squares), cell #2 (20 nm ZrO2, in green circles), cell #3 (40 nm ZrO2, in magenta diamonds) and cell #4 (60 nm ZrO2, in blue pentagons), showing the significant decrease of Rs and Rtotal of the coated cells except Rs of cell #2. (c) Bode plot of cell #1, cell #2, cell #3 and cell #4 showing the trend of the intermediate-frequency arc in the range of 1–100 Hz. (d) Cross section TEM image shows the ~40 nm porous nano ZrO2 layer on the LSM/YSZ backbone. The insert plan-view image shows that the ZrO2 surface layer is nano-grained and porous. The blue-arrowed areas are mesopores randomly distributed through the entire ZrO2 surface layer. (e), TEM image shows no significant change of ALD ZrO2 surface layer after 400 hours operation.
Mentions: In the present work, a total of seven cells with six of the cells having differently engineered surface architectures on the cathode were investigated. All the cells and their corresponding performances are listed in Table 1. For three cells (#2, #3 and #4), a pure ZrOx layer was deposited by ALD onto the LSM/YSZ cathode backbone of commercial anode-supported SOFCs. The as-deposited state of the ZrOx layer is amorphous and conformal on the cathode backbone. By controlling the ALD processing cycles, a uniform layer with thickness of 20, 40 and 60 nm was deposited on the cathode of three cells, respectively. All cells were subjected to heat treatment to crystallize the ZrO2 structure before cell operation. Subsequently, an electrochemical test was performed at 750 °C in H2 and air for anode and cathode, respectively. In comparison with the baseline cell (cell #1), power density increases were observed for all three cells (in Table 1). In particular, as shown in Fig. 1a–c, a large power density increase by a factor of 1.5, accompanied by the simultaneous large decrease of both series resistance Rs and polarization resistance Rp was observed for cell #3 with 40 nm ZrO2 coating layer.

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.


Related in: MedlinePlus