Tuning ORR electrocatalytic functionalities in CGFO-GDC composite cathode for low-temperature solid oxide fuel cells

Mixed ionic and electronic conduction (MIEC) in the composite cathode can alter oxygen stoichiometry and other physiochemical properties, eventually promoting the electrocatalytic functionalities for oxygen reduction reaction (ORR) at low operational temperatures (<650 °C). Here, we demonstrate a composite cathode of CoGd_0.8Fe_1.80O₄ /Gd_0.10Ce_0.9O_2?δ (CGFO-GDC), which delivers low electrode polarization resistance of 0.60 Ω cm² at 550 °C. The best-performing sample CGFO-GDC exhbits the peak power density (PPD) of 611-343 mW cm^?2 at 550-470 °C under a fuel cell conditions. Moreover, durability measurement verifies CGFO-GDC as a chemically stable cathode with improved ORR catalytic functionality. Additionally, first principle calculations using density function theory (DFT) were also conducted to analyze the ion diffusion mechanism of fabricated CGFO-GDC cathode. Our findings certify that introducing ionic conducting GDC into CGFO sample improves the catalytic functionalities. As a result, the composite CGFO-GDC based SOFC delivers minimum electrode polarization resistance with improved power output owing to its enhanced oxygen vacancies and fast catalytic reactions at 550 °C.     

Modeling of cooperative defect transport and thermal mismatch in a planar solid oxide fuel cell

Mixed ionic-electronic conducting (MIEC) membranes are widely applied as cathode material in solid oxide fuel cells (SOFCs). Nonetheless, the chemical expansion of an MIEC membrane caused by point defects (oxygen vacancies and small polarons) during oxygen transport induces cell failure. In this study, a multilayer thermo-chemical-mechanical model was proposed to consider defect diffusion under sudden changes in the cathode atmosphere, thermal expansion mismatch, and mechanical bending deformation. Under the set boundary conditions, the overall structural curvature of the multilayer system was relieved when the cathode was subjected to a high tensile stress. The influences of relevant parameters on the transient stress field were also investigated, and the overall stress of the multilayer structure decreased significantly when the oxygen partial pressure in the inlet channel was constrained. Reducing the sintering temperature and chemical expansion coefficient could improve the reliability of the planar SOFC. In addition, the effect of constraints in different directions on the multilayer system stresses is also investigated. This study provides theoretical support for use in designing the stabilities and gas supply strategies of planar solid fuel cells.     

Enhanced electrocatalytic activity and stability of Pd-based bimetallic icosahedral nanoparticles towards alcohol oxidation reactions

Modulating components and surface structure of Pd-based nanomaterials were efficient strategies to improve electro-catalytic activity. Bimetallic Pd-based nano-catalysts with core-shell or alloy structure are reported to be promising for fuel cell reactions. In this work, we have successfully constructed PdCu@Pd core-shell icosahedral nano-catalysts via the hydrothermal method. Based on this method, we have successfully synthesized alloyed PdPt icosahedrons, PdAg icosahedrons, and monometallic Pd icosahedrons. Among all nanoparticles as prepared, PdCu@Pd core-shell icosahedral nano-catalyst exhibits the highest mass activity to ethylene glycol oxidation reaction (EGOR) as 7.4 A mg⁻¹, which is 7.4 times higher than that of commercial Pd/C (1.0 A mg⁻¹). In addition, its mass activity for glycerol oxidation reaction (GOR) is 6.3 A mg⁻¹, which is 6.5 times higher than that of commercial Pd/C (0.96 A mg⁻¹). In the test of stability, PdCu@Pd core-shell icosahedral nano-catalyst keeps the highest current density throughout the time domain. The enhanced electro-catalytic performance can mainly attribute to the modification of electronic generated from strain between Pd shell and PdCu core as well as defect from twinned structure. This study can provide a reminder to researchers to further design novel Pd-based nano-catalysts by tuning surface structure and composition at the same time.