Concurrent Amorphization and Nanocatalyst Formation in Cu-Substituted Perovskite Oxide Surface: Effects on Oxygen Reduction Reaction at Elevated Temperatures.

The activity and durability of chemical/electrochemical catalysts are significantly influenced by their surface environments, highlighting the importance of thoroughly examining the catalyst surface. Here, Cu-substituted La0.6Sr0.4Co0.2Fe0.8O3-δ is selected, a state-of-the-art material for oxygen reduction reaction (ORR), to explore the real-time evolution of surface morphology and chemistry under a reducing atmosphere at elevated temperatures. Remarkably, in a pioneering observation, it is discovered that the perovskite surface starts to amorphize at an unusually low temperature of approximately 100 °C and multicomponent metal nanocatalysts additionally form on the amorphous surface as the temperature raises to 400 °C. Moreover, this investigation into the stability of the resulting amorphous layer under oxidizing conditions reveals that the amorphous structure can withstand a high-temperature oxidizing atmosphere (≥650 °C) only when it has undergone sufficient reduction for an extended period. Therefore, the coexistence of the active nanocatalysts and defective amorphous surface leads to a nearly 100% enhancement in the electrode resistance for the ORR over 200 h without significant degradation. These observations provide a new catalytic design strategy for using redox-dynamic perovskite oxide host materials.

Oxygen nonstoichiometry and thermodynamic quantities of Gd and Cu doped misfit-layered calcium cobaltites.

Hyperstoichiometric (p-type) misfit-layered calcium cobaltites have been studied as components in various high-temperature electrochemical devices. Multiple studies have reported their applications or physical properties, but systematic studies on their defect structures and thermodynamic quantities are still insufficient. In this study, the oxygen nonstoichiometry and the electrical conductivity of Gd-Cu co-doped misfit cobalt oxide were measured as functions of temperature and oxygen partial pressure, along with thermodynamic quantities. The behavior of oxygen nonstoichiometry could not be explained by a defect structure assuming the ideal solution, as it showed a positive deviation in Raoult's law. The redesigned nonideal proposed defect structure, considering that the deviation originated from the high concentration of degenerate holes, could describe the oxygen nonstoichiometry precisely; and in this process, the values of , , Nv, , γh, and were quantitatively extracted. These values were compared with those obtained for the undoped system. The total electrical conductivity was measured using a dense specimen obtained via spark plasma sintering, and the anisotropic nature of the material was confirmed.

Surface decorated spinel-oxide electrodes for mixed-potential ammonia sensor: Performance and DRT analysis.

The mixed-potential gas sensors appeared as the most promising sensing technology for the in-situ quantification of exhaust pollutants due to their simple configuration, low-cost, and thermochemical stability. Presently, high sensitivity and selectivity supplemented by long-term stability is the bottleneck challenge for these sensors to commercialize. Herein, highly sensitive and ammonia (NH3) selective mixed-potential gas sensors were developed using surface decorated CuFe2O4 (CFO)-MOX (M = Sn, Ni, Zn) composite sensing electrodes (SE). The CFO-NiO SE enriched of the surface oxygen vacancies produced a maximum response of -62 mV to 80 ppm NH3, supported by excellent sensitivity at 650 ℃. The comprehensive analysis of the response behavior and current-voltage (I-V) characteristics verified the sensing mechanism to be based upon the mixed-potential model conforming to the reaction-rate limited Butler-Volmer NH3 oxidation kinetics. Finally, the distribution of relaxation times (DRT) analysis of impedance spectra confirmed that the overall polarization resistance was invariable of the mass-transport processes and solely governed by the extent of interfacial redox reactions proceeding at the triple-phase boundaries (TPB). Moreover, the high sensitivity, selectivity, and exceptional stability over five months substantiate the suitability of the presented sensor as a potential candidate for in-situ ammonia quantifications in industrial and automotive applications.