| 摘要: | 質子傳導型固態氧化物燃料電池(Proton-conducting solid oxide fuel cells, P-SOFCs)於500-800 ℃擁有優秀的質子傳導性。但隨著工作溫度降低，使得P-SOFC能夠在較低溫運行，然而工作溫度下降也導致陰極(Oxygen reduction reaction, ORR)反應速率降低，因此如何提高ORR的反應速率尤為重要。
在傳統P-SOFC中，反應位點僅在電解質與陰極的界面，因此需要增加更多的反應位點，將能夠傳遞質子的材料及電子與離子混合導體(Mixed Ionic Electronic Conductor, MIEC)一同製成陰極功能層，便能夠縮短離子需傳遞的距離，並增加三相界面(Triple Phase Boundaries, TPBs)，進而降低極化阻抗，提升性能。陰極功能層的加入亦能改善陰極和電解質材料因熱膨脹係數不匹配，在長時間的運行下界面分層的問題。
脈衝雷射沉積(Pulsed laser deposition, PLD)能夠製造出成分高度均勻且一致的薄膜，且成分與靶材的化學劑量比相同。本研究使用PLD技術製備LSCF-BCZYYb陰極功能層，並與旋轉塗佈樣品比較。
結果顯示LSCF與BCZYYb在PLD後會有二次相形成，因而影響性能。在800 °C時，PLD電池的開路電壓(Open circuit voltage, OCV)僅有0.73V，並且600 °C的RH卻小於700 °C的RH，因此認為PLD電池存在短路的問題。旋轉塗佈則無短路問題，隨著溫度降低，熱驅動力下降，RH也隨著增加；RL主要是由於水氣的累積，由於持續運作，造成氣體愈加不易擴散，使得RL上升。由於以PLD製備之電池存在短路問題，無法與旋轉塗佈製備之電池比較，然而從材料分析結果仍可得知，LSCF和BCZYYb在PLD後無法維持其結構，並形成二次相，因此不適用於PLD。
本研究亦統整先前研究之結果，並根據不同參數進行比較。
GCCCO-BCZY透過PLD可製造出均勻一致的薄膜，並形成相互連通的網狀結構，使有效面積顯著提升。旋轉塗佈法因GCCCO和BCZY的燒結溫度限制，顆粒間連結性較差，導致性能不如PLD製備的電池。此外，LSCF和BCZYYb由於在PLD後無法保持原有結構，並形成SrZrO3，因此不適合應用在PLD製程中。
GCCCO作為TCO材料因為可以同時傳輸三種離子，與LSCF相比，更適合作為陰極材料。因此將GCCCO-BCZYYb製備於商用半電池之電池取的優異的表現。然而當將兩者分別作為陰極功能層材料製備於自製半電池上時，LSCF電池性能較高，此結果差異尚待更多資訊來釐清。
自製半電池的電解質晶粒尺寸小，晶界多，並且陽極燒結程度也較高，減少電子傳輸通道及氫氧化反應(Hydrogen oxidation reaction, HOR)面積，導致阻抗值大於使用商用半電池製成之電池。當降低半電池燒結溫度並減少電解質厚度，Ro及Rp下降。因此降低半電池燒結溫度，以及減少晶界數量，並降低電解質厚度，有助於提升電池的性能。
由於乾壓製程中並未添加分散劑及黏結劑等聚合物，其造孔劑分散性較刮刀基板低，導致界面接觸較差，並提高氣體傳輸難度，使Ro及RL增加。採用乾壓法製備陽極基板需提高造孔劑的分散性，或是使用不易團聚的造孔劑。
與澱粉相比，紙纖維形成足夠大且互相連接的圓柱型孔洞，提供氣體傳輸，並增加HOR反應位點的氣體濃度，提高反應速率，進而提高陰極側ORR反應速率，使Rp降低。此結果證明紙纖維較澱粉適合作為陽極之造孔劑使用。
;Proton-conducting solid oxide fuel cells (P-SOFCs) exhibit excellent proton conductivity at 500-800 °C. However, as the operating temperature decreases, enabling P-SOFCs to operate at lower temperatures, the oxygen reduction reaction (ORR) rate at the cathode also decreases. Thus, improving the ORR reaction rate is particularly important.
In traditional P-SOFCs, the reaction sites are only at the interface between the electrolyte and the cathode. Therefore, by incorporating proton-conducting materials into the cathode functional layer together with mixed ionic-electronic conductors (MIECs) to add more reaction sites, the ion transmission distance can be shortened and the three-phase boundaries (TPBs) can be increased. Thereby reducing polarization resistance and improving performance. Adding a cathode functional layer can also improve the interfacial delamination problem due to the mismatch of thermal expansion coefficients between the cathode and electrolyte materials during long-term operation.
Pulsed laser deposition (PLD) can produce highly uniform and consistent thin films, maintaining the same chemical stoichiometry as the target material. This study uses PLD technology to fabricate LSCF-BCZYYb cathode functional layers and compares them with samples prepared by spin coating.
The results show that a secondary phase forms in LSCF and BCZYYb after PLD, which affects performance. At 800 °C, the open circuit voltage (OCV) of the PLD cell is only 0.73V, and the higher-frequency polarization resistance (RH) at 600 °C is less than that at 700 °C, indicating a short-circuit issue in the PLD cell. The spin-coated cell does not have short-circuit problems. As the temperature decreases, the thermal driving force decreases, and RH increases. The RL mainly results from water vapor accumulation; continuous operation makes gas diffusion increasingly difficult, leading to an increase in RL. Due to the short-circuit issue in the PLD-prepared cell, it cannot be compared with the spin-coated cell. However, material analysis still indicates that LSCF and BCZYYb cannot maintain their structure after PLD and form a secondary phase, making them unsuitable for PLD.
This study also compiles the results of previous research and compares them based on different parameters.
GCCCO-BCZY, fabricated through PLD, produces conformal and coherent films and forms an interconnected network structure, significantly increasing the effective area. In contrast, the spin coating method results in poorer particle connectivity due to the sintering temperature limitations of GCCCO and BCZY, leading to lower performance compared to PLD-fabricated cells. Additionally, LSCF and BCZYYb, unable to maintain their original structure after PLD and forming SrZrO3, are not suitable for application in the PLD process.
As a TCO material, GCCCO can transport three types of ions simultaneously, making it more suitable as a cathode material compared to LSCF. Therefore, GCCCO-BCZYYb, when fabricated into commercial half-cells, exhibits excellent performance. However, when these two materials were used separately as cathode functional layer materials in in-house half-cell, the LSCF battery showed higher performance. This discrepancy requires further information to be clarified.
The grain size of electrolyte in in-house half-cells is small with many grain boundaries, and the anode has a higher degree of sintering, reducing electron transport pathways and hydrogen oxidation reaction (HOR) areas, leading to higher impedance values compared to cells made from commercial half-cells. Reducing the sintering temperature of the half-cells and decreasing the electrolyte thickness lower Ro and Rp. Therefore, reducing the sintering temperature of the half-cells, decreasing the amount of grain boundaries, and reducing electrolyte thickness help improve cell performance.
Due to the absence of dispersants and binders in the dry pressing process, the pore former dispersion is lower than that of the tape casting substrates, resulting in poorer interfacial contact and increased gas transport difficulty, thus increasing Ro and RL. Enhancing the dispersion of the pore former or using a pore former that is less prone to agglomeration is necessary for preparing anode substrates using the dry pressing method.
Compared to starch, paper fibers form sufficiently large and interconnected cylindrical pores, providing gas transport and increasing gas concentration at HOR reaction sites, thereby improving reaction rates and ORR reaction rates at the cathode side, reducing Rp. This result demonstrates that paper fibers are more suitable as a pore former for the anode compared to starch. |
