Yi-Lin Huang

Chromium Poisoning Effects on Surface Exchange Kinetics of La0.6Sr0.4Co0.2Fe0.8O3−δ

The presence of Cr has already been reported in literature to cause severe degradation to La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF). However, fundamental understanding of Cr effects on the surface exchange kinetics is still lacking. For the first time, in situ gas phase isotopic oxygen exchange was utilized to quantitatively determine Cr effect on oxygen exchange kinetics of LSCF powder as a function of temperature and water vapor. Our investigations revealed that the formation of secondary phases such as SrCrO4, Cr2O3, Cr-Co-Fe-O, and La-Co-Fe-O can affect both the oxygen dissociation step and overall surface exchange. Specifically, Cr-containing secondary phases on the surface not only decrease the active sites for surface reactions but also alter the nearby stoichiometry of the LSCF matrix, thereby limiting surface oxygen transport. In addition, water molecules actively participate in the surface reactions and can further block the active sites.

Direct observation of enhanced water and carbon dioxide reactivity on multivalent metal oxides and their composites

Electrochemical gas–solid reactions are important for many energy technologies, involving partial pressure dependent surface catalysis and bulk conduction phenomenon unresolvable using conventional techniques. We report for the first time water and CO2 reactivity on perovskites, fluorites, and their composites across a wide temperature- oxygen partial pressure (pO2) range by in situ gas phase isotopic oxygen exchange, demonstrating that multivalent metal oxides actively “breathe” oxygen from these gasses. We reveal the importance of cation oxidation state and the roles of electronic, ionic, and mixed conductor phases, as well as their composites. Moreover, we show that an ionic and electronic conducting oxide composite dramatically modifies the kinetics of oxygen exchange as compared to these materials individually or as compared to the effect of creating a composite from two mixed conducting oxides.

Three Dimensional Microstructural Characterization of Cathode Degradation in SOFCs Using FIB/SEM and TEM

Solid oxide fuel cells (SOFC) present an efficient, clean, and flexible means of energy conversion, but the limited durability of the cells in practical applications has impeded their commercial adoption. Degradation occurs within the cathode upon long-term operation and exposure to various environmental contaminants, including H2O. The contaminants cause significant microstructural and compositional changes within the cathode that adversely affect activation, polarization mechanisms, and ionic and electronic conductivities. Previous works have demonstrated that a number of quantifiable microstructural characteristics can be directly related to SOFC performance, the most important of these being triple phase boundary length (LTPB) and pore surface area [1-2]. These parameters have not been examined during cell degradation, and further analysis under these conditions provides insight into specific cell degradation mechanisms, informing future fabrication and operation criteria.

Highly Performing Chromate-Based Ceramic Anodes (Y0.7Ca0.3Cr1–xCuxO3−δ) for Low-Temperature Solid Oxide Fuel Cells

Exploitation of alternative anode materials for low-temperature solid oxide fuel cells (LT-SOFCs, 350-650 °C) is technologically important but remains a major challenge. Here we report a potential ceramic anode Y0.7Ca0.3Cr1- xCu xO3-δ ( x = 0, 0.05, 0.12, and 0.20) (YCC) exhibiting relatively high conductivity at low temperatures (≤650 °C) in both fuel and oxidant gas conditions. Additionally, the newly developed composition (YCC12) is structurally stable in reducing and oxidizing gas conditions, indicating its suitability for SOFC anodes. The I- V characteristics and performance of the ceramic anode infiltrated with Ni-(Ce0.9Gd0.1O2-δ)(GDC) were determined using GDC/(La0.6Sr0.4CoO3-δ)(LSC)-based cathode supported SOFCs. High peak power densities of ∼1.2 W/cm2 (2.2A/cm2), 1 W/cm2 (2.0A/cm2), and 0.6 W/cm2 (1.3 A/cm2) were obtained at 600, 550, and 500 °C, respectively, in H2/3% H2O as fuel and air as oxidant. SOFCs showed excellent stability with a low degradation rate of 0.015 V kh-1 under 0.2 A/cm2. YCC-based ceramic anodes are therefore critical for the advancement of LT-SOFC technology.

Nanointegrated, High-Performing Cobalt-Free Bismuth-Based Composite Cathode for Low-Temperature Solid Oxide Fuel Cells

Cost-effective cathodes that actively catalyze the oxygen reduction reaction (ORR) are one of the major challenges for the technological advancement of low-temperature solid oxide fuel cells (LT-SOFCs). In particular, cobalt has been an essential element in electrocatalysts for efficiently catalyzing the ORR; nevertheless, the cost, safety, and stability issues of cobalt in cathode materials remain a severe drawback for SOFC development. Here, we demonstrated that by appropriate nanoengineering, we can overcome the inherent electrocatalytic advantages of cobalt-based cathodes to achieve comparable performance with a cobalt-free electrocatalyst on a bismuth-based fast oxygen ion-conducting scaffold that simultaneously enhances the performance and stability of LT-SOFCs. Consequently, the peak power density of the SOFCs reaches 1.2 W/cm2 at 600 °C, highest performance of a cobalt-free-based cathode that has been ever reported. In addition, by the surface-protecting effect of covered nanoelectrocatalysts, the evaporation of highly volatile bismuth is greatly suppressed, resulting in an 80% improvement in performance durability, the best among all reported bismuth-based fuel cells.