| 摘要: | 質子傳輸型陶瓷燃料電池(Protonic ceramic fuel cells, PCFCs)材料在500-800 ℃之操作溫度範圍內具有優良傳導性以及提高材料的穩定性且密封性較佳，但降低操作溫度會影響空氣電極的氧還原反應(Oxygen reduction reaction, ORR)速率。當空氣電極端使用Nd-based材料比La-based材料具有更高的氧交換率。由於Nd-based材料優異的氧交換速率，在空氣電極側可產生更快速的氧離子傳輸和氧擴散速率，藉此有效降低電化學阻抗並提升電化學性能。
在本研究中，使用NdxLa0.6-xSr0.4Co0.2Fe0.8O3-δ (x=0, 0.1, 0.2, 0.3, 0.6)奈米纖維作為PCFC的空氣電極。結果顯示，Nd摻雜LSCF電池可以有效提升性能，因Nd3+的離子半徑小於La 3+的離子半徑，導致平均A-site離子半徑改變，降低了氧遷移至空位的阻礙，使氧跳躍到氧空位所受到晶格應力減弱。
Nd0.1-LSCF電池在800°C 時的最高功率密度約為579.16 mW/cm2，比LSCF電池高 43%。歐姆電阻和極化電阻分別降低了約29% 和32%。使用Nd0.1-LSCF電池進行電解模式，空氣電極側電解水氣並於氫氣電極側產生氫氣。其法拉第電流效率達87%，能量轉換效率達85%，而產氫速率可達10.17 ml/min。
本研究結果可知，Nd0.1-LSCF奈米纖維在PCFC可以有效提升氧擴散速率與氧離子傳輸，且在800 ℃操作溫度PCFC之電化學性能表現良好具有最高功率密度579.16 mW/cm2。Nd0.1-LSCF電池成功應用於PCEC電池模式。Nd0.1-LSCF奈米纖維空氣電極提供於質子傳導型陶瓷電化學電池裝置未來發展之潛力。;Operation of PCFCs in the range of 500-800 °C range would enhance the durability of materials but reduce the rate of oxygen reduction reaction (ORR) at air electrode. Nd-based cathode material has higher oxygen exchange rate than La-based ones. Due to the excellent oxygen exchange rate, rapid oxygen anion transport and oxygen surface exchange can decrease electrochemical impedance when the Nd-based cathode material is used as an air electrode.
In this research, the NdxLa0.6-xSr0.4Co0.2Fe0.8O3-δ (x=0, 0.1, 0.2, 0.3, 0.6) nanofiber is used as the air electrode for PCFCs. The cell with Nd doped LSCF can effectively promote the performance. The smaller cation radius of Nd3+ than that of La3+ causes a difference in the average A-site ion radii that has a relationship with lattice strain during oxygen hopping to oxygen vacancy.
The peak power density of Nd0.1-LSCF cell under PCFC mode at 800 °C is about 579.16 mW/cm2, 43% higher than that of LSCF cell. The ohmic resistance and polarization resistance are decreased by about 29% and 32%, respectively.
When PCFC is operated under protonic ceramic electrolysis cells (PCEC) mode, water vapor is supplied to the oxygen electrode side and thus pure H2 is generated at the hydrogen electrode side. The Faraday’s efficiency (FE) of Nd0.1-LSCF cell is 87% and the energy conversion efficiency (ECE) is 85%. The hydrogen evolution rate can achieve 10.17 ml/min.
From the results of this study, the Nd0.1-LSCF nanofiber m can enhance the transmission of oxygen ions and the diffusion of oxygen in air electrode, also keeping the outstanding performance of PCFC, with a peak power density of 579.16 mW/cm2 at 800 °C. Nd0.1-LSCF cell can be successfully operated under PCEC mode. The N0.1-LSCF nanofiber air electrode provided great potential for the future development of protonic ceramic electrochemical cell device. |
