KINETICS AND PERFORMANCE OF PEROVSKITE ANODES FOR METHANE ELECTRO-OXIDATION IN SOLID OXIDE FUEL CELLS
Venue: 16 May 2020, Saturday at 11:00AM
Through: MS-Teams web link
ABSTRACT
Perovskite anode materials with impregnated and doped electrocatalytic elements have been synthesized and tested in solid oxide fuel cells (SOFCs) to study their kinetics and performance for methane electrooxidation. In the initial stages, the efficient electrocatalyst combinations for methane electro-oxidation is studied. Various oxides like cerium oxide (CeO2), cobalt oxide (Co3O4), iron oxide (Fe3O4) and copper oxide (CuO) were impregnated over the nickel cermet (N-Y) to yeild Ce-N-Y, Co-N-Y, Fe-N-Y and Cu-N-Y anodes. The kinetics of impregnated cermet anodes were studied using a three-electrode set up with an asymmetric reference electrode and the electrochemical rate constant, exchange current density (i0) is estimated. The CeO2-Ni and Co3O4-Ni combinations in Ce-N-Y and Co-N-Y anodes perform better compared to all other combinations with maximum power density of 436 mW cm-2 in CH4. In the later stages of the study, uni-doped (La0.3Sr0.5TiO3-δ, LSTA-) and bi-doped (La0.3Y0.1Sr0.4TiO3-δ, LYSTA-) perovskites anodes are synthesized using solid state route and the oxide of nickel (Ni) is impregnated into the porous structure of full cells containing LSTA- and LYSTA- anode using infiltration technique to yield (04)LSTA- and (04)LYSTA- anodes. The kinetics of impregnated perovskite anodes, (04)LSTA- and (04)LYSTA-, were studied similar to impregnated cermet anodes and i0 values are estimated. The i0 values of (04)LSTA- and (04)LYSTA- anodes were 25.3 mA cm-2 (8.9 mA cm-2 ) and 20 mA cm-2 (7.5 mA cm-2 ) in H2 (CH4). The obtained i0 values were higher compared to traditional nickel cermet anodes of 3.1 mA cm-2 (1.8 mA cm-2 ) in H2 (CH4). But, still the performance of (04)LSTA- and (04)LYSTA- anodes were annihilated in CH4 environment. To improve the performance in CH4 environment, cerium oxide (CeO2) is impregnated along with NiO to yield (84)LSTA- and (84)LYSTA-anodes. The i0 values of (84)LSTA- and (84)LYSTA- anodes were 154.6 mA cm-2 (123.5 mA cm-2) and 161.6 mA cm-2 (133.2 mA cm-2 ) in H2 (CH4) which were higher compared to Ce-N-Y in H2 (121.8 mA cm-2 ) and CH4 (83.3 mA cm-2 ). The (84)LSTA- and (84)LYSTA- anodes yielded a maximum power density of 490 mW cm-2 and 430 mW cm-2 which was higher compared to Ce-N-Y anode in CH4. The impregnated perovskite anodes were also compared with doped perovskite anodes, La0.3Sr0.5Ni0.04Ti0.96O3-δ(LSN0.04TA-), La0.3Sr0.5Ni0.16Ti0.84O3-δ (LSN0.16TA-) and La0.3Y0.1Sr0.4Ni0.04Ti0.96O3-δ (LYSN0.04TA-) where the former outperformed the later in terms of performance. The reasons for annihilated performance of doped perovskites were correlated to the structure-property relationship of the tailored perovskites. Finally, the improved performance of (84)LSTA- and (84)LYSTA- anodes is attributed to the combination of mixed ionic and electronic conduction, oxygen vacancies in perovskite and induced metal support interactions between Ni-CeO2 as observed using x-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR) and chemisorption studies. In addition, other physical characterization techniques such as X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), energy-dispersive analysis of X-ray spectroscopy (EDAX), high resolution transmission electron microscope (HRTEM), Raman spectroscopy and photoluminescence spectroscopy were carried out to assess the phase purity, microstructure, presence of constituent elements, carbon deposits and oxygen vacancies in tailored anodes, respectively.