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The correlation between the surface chemistry and electronic structure is studied for SrTi 1-x Fe x O 3 (STF), as a model perovskite system, to explain the impact of Sr segregation on the oxygen reduction activity of cathodes in solid oxide fuel cells. Dense thin films of SrTi 0.95 Fe 0.05 O 3 (STF5), SrTi 0.65 Fe 0.35 O 3 (STF35) and SrFeO 3 (STF100) were investigated using a coordinated combination of surface probes. Composition, chemical binding, and valence band structure analysis using angle-resolved x-ray photoelectron 10 spectroscopy showed that Sr enrichment increases on the STF film surfaces with increasing Fe content. In situ scanning tunnelling microscopy / spectroscopy results proved the important and detrimental impact of this cation segregation on the surface electronic structure at high temperature and in oxygen environment. While no apparent band gap was found on the STF5 surface due to defect states at 345 o C and 10 -3 mbar of oxygen, the surface band gap increased with Fe content, 2.5 ± 0.5 eV for STF35 and 3.6 ± 0.6 eV for 15 STF100, driven by a down-shift in energy of the valence band. This trend is opposite to the dependence of the bulk STF band gap on Fe fraction, and is attributed to the formation of a Sr-rich surface phase in the form of SrO x on the basis of the measured surface band structure. The results demonstrate that Sr segregation on STF can deteriorate oxygen reduction kinetics through two mechanisms -inhibition of electron transfer from bulk STF to oxygen species adsorbing onto the surface, and the smaller 20 concentration of oxygen vacancies available on the surface for incorporating oxygen into the lattice. IntroductionBecause of their high efficiency and fuel flexibility, solid oxide fuel cells (SOFCs) offer the potential to contribute significantly to a clean energy infrastructure 1, 2 . However, their high working 25 temperatures (>800 o C) impose challenges due to accelerated materials degradation and high cost. The lowering of the working temperature has, therefore, become a strong focus of research. 3 At reduced temperatures (<700 o C), slow Oxygen Reduction Reaction (ORR) kinetics at the cathode become a major barrier to 30 the implementation of high performance SOFCs. To rationally design new cathode materials with high ORR activity, it is necessary to understand the governing ORR mechanisms and identify key descriptors of the cathode materials that directly control ORR activity. The strength of oxygen adsorption and the 35 energy barriers to oxygen dissociation, reduction and incorporation are believed to be the processes that determine oxygen reduction activity on perovskite oxides. 4,5 The energetics of these processes depends, in part, on the cathode electronic structure. In transition metal catalysis, the d-40 band structure 6 is a well-established descriptor of ORR activity. However, the applicability of the d-band model to perovskite oxide SOFC cathodes is limited by their complex surface chemistry (an anion and two cation sublattices), the role of oxygen vacan...

Unlike the more established lithium-ion based energy storage chemistries, the complex intercalation chemistry of multivalent cations in a host lattice is not well understood, especially the relationship between the intercalating species solution chemistry and the prevalence and type of side reactions. Among multivalent metals, a promising model system can be based on nonaqueous Zn2+ ion chemistry. Several examples of these systems support the use of a Zn metal anode, and reversible intercalation cathodes have been reported. This study utilizes a combination of analytical tools to probe the chemistry of a nanostructured δ-MnO2 cathode in association with a nonaqueous acetonitrile–Zn­(TFSI)2 electrolyte and a Zn metal anode. As many of the issues related to understanding a multivalent battery relate to the electrolyte–electrode interface, the high surface area of a nanostructured cathode provides a significant interface between the electrolyte and cathode host that maximizes the spectroscopic signal of any side reactions or minor mechanistic pathways. Numerous factors affecting capacity fade and issues associated with the second phase formation including Mn dissolution in heavily cycled Zn/δ-MnO2 cells are presented including dramatic mechanistic differences in the storage mechanism of this couple when compared to similar aqueous electrolytes are noted.

Population maps of the corpus callosum (CC) and cortical lobe connections were generated by combining cortical gray matter parcellation with the diffusion tensor fiber tractography of individual subjects. This method is based on the fact that the cortical lobes of both hemispheres are interconnected by the corpus callosal fibers. T1-weighted structural MRIs and diffusion tensor MRIs (DT-MRI) of 22 right-handed, healthy subjects were used. Forty-seven cortical parcellations in the dorsal prefrontal cortex, ventral prefrontal cortex, sensory-motor cortex, parietal cortex, temporal cortex, and occipital cortex were semi-automatically derived from structural MRIs, registered to DT-MRI, and used to identify callosal fibers. The probabilistic connections to each cortex were mapped on entire mid-sagittal CC voxels that had anatomical homology between subjects as determined by spatial registration. According to the population maps of the callosal connections, the ventral prefrontal cortex and parts of the dorsal prefrontal cortex both project fibers through the genu and rostrum. The CC regions through which the superior frontal cortex passes extend into the posterior body. Fibers arising from the parietal lobe and occipital lobe run mainly through the splenium, while fibers arising from the sensory-motor cortex pass through the isthmus. In general, dorsal or medial cortical lobes project fibers through the dorsal region of the CC, while lateral cortical lobes project fibers through the ventral region of the CC. The probabilistic subdivision of the CC by connecting cortical gray matter provides a more precise understanding of the CC.