Publication: Enhancement of perovskite type cathode material via composite cathode modification at intermediate temperature solid oxide fuel cells
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Date
2023-05-01
Authors
Ahmad Fuzamy Bin Mohd Abd Fatah
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Abstract
In the past decade, researchers have strengthened Solid Oxide Fuel Cells (SOFCs) durability and stability at high temperatures to make them economically viable. However, the application of SOFCs at high temperatures leads to rapid cathode degradation. As a result, cathode adjustment is required to ensure that the cathode can operate at temperatures below 1000 ºC to avoid degradation. In this study, Lanthanum Strontium Cobalt Ferrite (LSCF) cathode was composited with nickel oxide, copper oxide, and zinc oxide with an aim to enhance the catalytic activity of a cell operating at a moderate temperature (600-800 ºC) (Intermediate Temperature Solid Oxide Fuel Cell – IT-SOFC). This study has been divided into three parts namely initial evaluation and optimization, morphology on the cathode surface and performance evaluation of the single cell at intermediate temperature. Preliminary evaluation (thermal, bonding and phase analysis) shows that LSCF-NiO, LSCF-CuO and LSCF-ZnO achieve complete perovskite formation after calcined at temperature of 800 ºC. Thermal analysis showed that LSCF powder started to form at a temperature of 570 ºC followed by bond analysis that showed minimal carbonate bond formation at a temperature of 800 ºC. Furthermore, the phase analysis showed that the formation of LSCF reached 99% and above after the LSCF powder was calcined at a temperature of 800 ºC. The optimization process shows that the best ratio content of LSCF and metal oxide (NiO, CuO, ZnO) is 95 wt.% of LSCF and 5 wt.% of metal oxide. A deeper analysis also found that LSCF-CuO gave the lowest area specific resistance (ASR) and the highest active surface area compared to LSCF-NiO and LSCF-ZnO. Surface morphology was also carried out on LSCF-NiO, LSCF-CuO and LSCF-ZnO cathode surfaces. Surface morphology revealed strong adhesion between the cathode/electrolyte/anode layer and uniform nanosized particles indicating that each region was sintered at an appropriate temperature (sintering temperature cathode: 1100 ºC, sintering temperature anode: 1200 ºC). EDX and key mapping also reveal a cathode of exceptional purity with a uniform distribution of element on its surface. Analysis from the Bode plot also shows that LSCF-NiO, LSCF-CuO and LSCF-ZnO cathode composites have successfully increased the oxygen reduction reaction (ORR) capability when the cathode composite shows a significant reduction in the low-frequency impedance arc (P1). The results of the study also found that LSCF-CuO gave the lowest low-frequency impedance curve value (P1) overall compared to LSCF-NiO and LSCF-ZnO when the analysis was carried out at a temperature of 800 ºC. Electrochemical analysis showed that LSCF-NiO, LSCF-CuO and LSCF-ZnO single cell can operate at temperatures as low as 650 ºC and are able to exhibit an increase in power density as high as 26.27% after 5 wt.% copper oxide is added to LSCF cathode. Overall, the addition of transition class metal oxides (NiO, CuO, ZnO) has successfully increased the ORR reaction on LSCF cathodes. Studies from electrochemical analysis, active surface area and single cells show that the addition of 5 wt.% copper oxide to LSCF provide the best results in term of lowest ASR value, highest specific surface area and highest power density compared to nickel oxide and zinc oxide.