The hetero-interfaces between the perovskite (La 1Àx Sr x )CoO 3 (LSC 113 ) and the Ruddlesden-Popper (La 1Àx Sr x ) 2 CoO 4 (LSC 214 ) phases have recently been reported to exhibit fast oxygen exchange kinetics.Vertically aligned nanocomposite (VAN) structures offer the potential for embedding a high density of such special interfaces in the cathode of a solid oxide fuel cell in a controllable and optimized manner.In this work, VAN thin films with hetero-epitaxial interfaces between LSC 113 and LSC 214 were prepared by pulsed laser deposition. In situ scanning tunneling spectroscopy established that the LSC 214 domains in the VAN structure became electronically activated, by charge transfer across interfaces with adjacent LSC 113 domains above 250 C in 10 À3 mbar of oxygen gas. Atomic force microscopy and X-ray photoelectron spectroscopy analysis revealed that interfacing LSC 214 with LSC 113 also provides for a more stable cation chemistry at the surface of LSC 214 within the VAN structure, as compared to single phase LSC 214 films. Oxygen reduction kinetics on the VAN cathode was found to exhibit approximately a 10-fold enhancement compared to either single phase LSC 113 and LSC 214 in the temperature range of 320-400 C. The higher reactivity of the VAN surface to the oxygen reduction reaction is attributed to enhanced electron availability for charge transfer and the suppression of detrimental cation segregation.The instability of the LSC 113/214 hetero-structure surface chemistry at temperatures above 400 C, however, was found to lead to degraded ORR kinetics. Thus, while VAN structures hold great promise for offering highly ORR reactive electrodes, efforts towards the identification of more stable heterostructure compositions for high temperature functionality are warranted.

To simulate realistic operating conditions in SOFC systems, we investigate the influence of thermal cycling on the performance of electrolyte-supported planar SOFCs. Thermal cycling is often associated with interruption of fuel supply, with three main modes; hot standby, cold standby, and shutdown. Cell performance degradation is most significant during shutdown cycles. Nickel oxidation and agglomeration are more pronounced when SOFCs are subjected to lower temperatures for longer periods of time, leading to significant performance degradation. Ostwald ripening at the anode leads to degradation as Ni grains increase in size with cycling. Ni particle precipitation on the anode zirconia grains and along electrolyte grain boundaries is found for the first time in shutdown cycling tests. When H 2 S is mixed with the fuel, the internal reforming reactions and electrode reactions are inhibited by sulfur poisoning of the Ni anodes, accelerating degradation. The SOFC cycling degradation mechanisms are discussed in detail. Solid oxide fuel cells (SOFCs) have several advantages including high efficiency, fuel flexibility, and utilization of non-noble metal, Pt-free catalysts, due to their relatively high operation temperature. Commercialization of SOFC systems for residential electric power applications began in Japan in 2011. Such systems are frequently stopped and restarted in normal operation, e.g. when power is not required, or in an emergency. Such start-stop operation results in thermal cycling, and is often associated with an interruption in fuel supply. Although it is well known that thermal and redox cycling under startstop operation deteriorates SOFC electrochemical performance, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] there are only a limited number of studies that systematically focus on this technologically relevant issue.Continuous SOFC stack operation with constant power output generally results in a gradual degradation in performance during long-term operation (SOFCs should run for up to a decade). However, SOFCs can suffer to a greater degree from changes in operation conditions. Due to thermal expansion mismatch between the different components, the cells can suffer from mechanical degradation mechanisms, such as delamination and crack formation with simple thermal cycling. Changes in atmosphere can result in more serious degradation. The influences of thermal cycling and current density cycling on cell degradation have been previously investigated.1-4 The change in volume causes Ni agglomeration. [5][6][7] Redox cycles are typically associated with oxidation of Ni particles at the anode. [8][9][10][11][12] Furthermore, redox cycling results in the formation of Ni hydroxides at a certain vapor pressure in oxidizing atmosphere, with a high water vapor concentration. 13,14 In real residential SOFC power units, cells and stacks are not subjected to these different conditions independently; the changes occur much more dynamically. Therefore, cycle durability studies should be performed using reali...

It is extremely important to understand the properties of supported metal nanoparticles at the atomic scale. In particular, visualizing the interaction between nanoparticle and support, as well as the strain distribution within the particle is highly desirable. Lattice strain can affect catalytic activity, and therefore strain engineering via e.g. synthesis of core-shell nanoparticles or compositional segregation has been intensively studied. However, substrate-induced lattice strain has yet to be visualized directly. In this study, platinum nanoparticles decorated on graphitized carbon or tin oxide supports are investigated using spherical aberration-corrected scanning transmission electron microscopy (Cs-corrected STEM) coupled with geometric phase analysis (GPA). Local changes in lattice parameter are observed within the Pt nanoparticles and the strain distribution is mapped. This reveals that Pt nanoparticles on SnO2 are more highly strained than on carbon, especially in the region of atomic steps in the SnO2 lattice. These substrate-induced strain effects are also reproduced in density functional theory simulations, and related to catalytic oxygen reduction reaction activity. This study suggests that tailoring the catalytic activity of electrocatalyst nanoparticles via the strong metal-support interaction (SMSI) is possible. This technique also provides an experimental platform for improving our understanding of nanoparticles at the atomic scale.

We report here the significant enhancement of catalytic activity of Ag-Pd bimetallic nanocatalysts with the formation of Ag-Pd catalysts having an average diameter of 4.2 AE 1.5 nm on TiO 2 nanoparticles using a two-step microwave (MW)-polyol method. Data obtained using XRD and STEM-EDS indicated that Ag-Pd bimetallic nanocatalysts consisted of Ag 82 Pd 18 alloy core and about 0.5 nm thick Pd shell, denoted as AgPd@Pd. The hydrogen production rate of AgPd@Pd/TiO 2 from formic acid, 16.00 AE 0.89 L g À1 h À1 , was 23 times higher than that of bare AgPd@Pd prepared under MW heating at 27 C. It was even higher by 2-4 times than the best Ag@Pd and CoAuPd catalysts at 20-35 C reported thus far. The apparent activation energy of the formic acid decomposition reaction using AgPd@Pd catalyst decreased from 22.8 to 7.2 kJ mol À1 in the presence of TiO 2 . Based on negative chemical shifts of the Pd peaks in the XPS data and the measured activation energies, the enhancement of catalytic activity in the presence of TiO 2 was explained by the lowered energy barrier in the reaction pathways because of the strong electron-donating effects of TiO 2 to Pd shells, which enhance the adsorption of formate to the catalyst and dehydrogenation from formate. † Electronic supplementary information (ESI) available: Temperature proles of reagent solutions in each experiment and STEM and STEM-EDS images of bare AgPd@Pd nanoparticles. See

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