A robust and active hybrid catalyst for facile oxygen reduction in solid oxide fuel cells

The sluggish oxygen reduction reaction (ORR) greatly reduces the energy efficiency of solid oxide fuel cells (SOFCs). Here we report our findings in dramatically enhancing the ORR kinetics and durability of the state-of-the-art La[subscript 0.6]Sr[subscript 0.4]Co[subscript 0.2]Fe[subscript 0.8]O[subscript 3](LSCF) cathode using a hybrid catalyst coating composed of a conformal PrNi[subscript 0.5]Mn[subscript 0.5]O[subscript 3](PNM) thin film with exsoluted PrOxnanoparticles. At 750°C, the hybrid catalyst-coated LSCF cathode shows a polarization resistance of ∼0.022 Ω cm[superscript 2], about 1/6 of that for a bare LSCF cathode (∼0.134 Ω cm[superscript 2]). Further, anode-supported cells with the hybrid catalyst-coated LSCF cathode demonstrate remarkable peak power densities (∼1.21 W cm[superscript -2]) while maintaining excellent durability (0.7 V for ∼500 h). Near Ambient X-ray Photoelectron Spectroscopy (XPS) and Near Edge X-Ray Absorption Fine Structure (NEXAFS) analyses, together with density functional theory (DFT) calculations, indicate that the oxygen-vacancy-rich surfaces of the PrOxnanoparticles greatly accelerate the rate of electron transfer in the ORR whereas the thin PNM film facilitates rapid oxide-ion transport while drastically enhancing the surface stability of the LSCF electrode

Long-Run and Short-Run Dynamics among the Sectoral Stock Indices: Evidence from Turkey

Abstract This paper investigates the short-run and long-run dynamics among the major sectoral stock indices of the Istanbul Stock Exchange over the period 1997-2011. Long-run relationship among these indices is analyzed by using both conventional Engle and Granger (1987) an

The impact of interest rate and exchange rate volatility on banks' stock returns and volatility: Evidence from Turkey

This paper investigates the effects of interest rate and foreign exchange rate changes on Turkish banks' stock returns using the OLS and GARCH estimation models. The results suggest that interest rate and exchange rate changes have a negative and significant impact on the conditional bank stock return. Also, bank stock return sensitivities are found to be stronger for market return than interest rates and exchange rates, implying that market return plays an important role in determining the dynamics of conditional return of bank stocks. The results further indicate that interest rate and exchange rate volatility are the major determinants of the conditional bank stock return volatility. (C) 2011 Elsevier B.V. All rights reserved

Consolidation and commercial bank net interest margins: Evidence from the old and new European Union members and candidate countries

This paper examines the effects of financial reforms on the determinants of commercial bank net interest margin in the banking systems of the new EU member countries and candidate countries by dividing the sample period (1995-2006) into two sub-periods: consolidation period (1995-2000) and post-consolidation period (2001-2006). The paper also compares the new and old EU members to check whether differences with respect to the determinants of net interest margins between these two groups of countries exist within the same time period. The results indicate that size and managerial efficiency are negatively and significantly related to net interest margins in the two sub-periods. Regulators should promote merger and acquisition and market entry in order to increase the scale and efficiency of banks operating in the sector. Exploitation of the scale economies seems to be important in decreasing the interest rate spread in the sampled banking sectors. The results further indicate that all macroeconomic variables are statistically insignificant in the second sub-period, suggesting that differences in macroeconomic fundamentals have decreased among the sampled countries due to the increased convergence process in recent years. As for the comparison of the new and old EU members, the results suggest that the financial and economic convergence between the new and old members has not been completed. Macroeconomic differences within the group and between the groups still exist. (C) 2010 Elsevier B.V. All rights reserved

Threshold catalytic onset of carbon formation on CeO 2 during CO 2 electrolysis: mechanism and inhibition

Carbon deposition from CO and other carbon-containing fuels is a major cause of the performance degradation of catalysts and electrocatalysts in many energy conversion devices, including low-temperature solid oxide cells (LT-SOCs). In this work, we present direct observation of carbon deposition on thin-film CeO2 electrodes at LT-SOC operating temperatures (450 °C) in a CO/CO2 atmosphere by in operando X-ray photoelectron spectroscopy. In contrast to the general view that CeO2 is a carbon tolerant material, significant carbon formation was observed on CeO2 during CO2 electrolysis, with no other catalyst present. Moreover, carbon deposition on CeO2 demonstrated an intriguing threshold onset formation against surface Ce3+ concentration. With the aid of Monte Carlo simulations, we propose the neighboring Ce3+-Ce3+ pairs to be a critical catalytic structure that facilitates carbon deposition from CO. Finally, we propose mitigation of carbon deposition on CeO2 by doping CeO2 with non-redox-active cations, and proved this concept using 50% Gd- and 50% Zr-doped CeO2 as an example system. These findings provide an in-depth understanding of the mechanism of carbon deposition on CeO2 during electrochemical reactions and can guide the design of carbon-resistant CeO2-based electrocatalysts. ©201

Electrochemistry of Magnesium Electrolytes in Ionic Liquids for Secondary Batteries

The electrochemistry of Mg salts in room-temperature ionic liquids (ILs) was studied using plating/stripping voltammetry to assess the viability of IL solvents for applications in secondary Mg batteries. Borohydride (BH₄^–), trifluoromethanesulfonate (TfO^–), and bis­(trifluoromethanesulfonyl)­imide (Tf₂N^–) salts of Mg were investigated. Three ILs were considered: l-<i>n</i>-butyl-3-methylimidazolium (BMIM)-Tf₂N, <i>N</i>-methyl-<i>N</i>-propylpiperidinium (PP13)-Tf₂N, and <i>N</i>,<i>N</i>-diethyl-<i>N</i>-methyl­(2-methoxyethyl)­ammonium (DEME⁺) tetrafluoroborate (BF₄^–). Salts and ILs were combined to produce binary solutions in which the anions were structurally similar or identical, if possible. Contrary to some prior reports, no salt/IL combination appeared to facilitate reversible Mg plating. In solutions containing BMIM⁺, oxidative activity near 0.8 V vs Mg/Mg²⁺ is likely associated with the BMIM cation, rather than Mg stripping. The absence of voltammetric signatures of Mg plating from ILs with Tf₂N^– and BF₄^– suggests that strong Mg/anion Coulombic attraction inhibits electrodeposition. Cosolvent additions to Mg­(Tf₂N)₂/PP13-Tf₂N were explored but did not result in enhanced plating/stripping activity. The results highlight the need for IL solvents or cosolvent systems that promote Mg²⁺ dissociation

Threshold catalytic onset of carbon formation on CeO 2 during CO 2 electrolysis: mechanism and inhibition

International audienceCarbon deposition from CO and other carbon-containing fuels is a major cause of the performance degradation of catalysts and electrocatalysts in many energy conversion devices, including low-temperature solid oxide cells (LT-SOCs). In this work, we present direct observation of carbon deposition on thin-film CeO 2 electrodes at LT-SOC operating temperatures (450 C) in a CO/CO 2 atmosphere by in operando X-ray photoelectron spectroscopy. In contrast to the general view that CeO 2 is a carbon tolerant material, significant carbon formation was observed on CeO 2 during CO 2 electrolysis, with no other catalyst present. Moreover, carbon deposition on CeO 2 demonstrated an intriguing threshold onset formation against surface Ce 3+ concentration. With the aid of Monte Carlo simulations, we propose the neighboring Ce 3+-Ce 3+ pairs to be a critical catalytic structure that facilitates carbon deposition from CO. Finally, we propose mitigation of carbon deposition on CeO 2 by doping CeO 2 with non-redox-active cations, and proved this concept using 50% Gd-and 50% Zr-doped CeO 2 as an example system. These findings provide an in-depth understanding of the mechanism of carbon deposition on CeO 2 during electrochemical reactions and can guide the design of carbon-resistant CeO 2-based electrocatalysts

Surface Defect Chemistry and Electronic Structure of Pr_0.1Ce_0.9O_2−δ Revealed <i>in Operando</i>

Understanding the surface defect chemistry of oxides under functional operating conditions is important for providing guidelines for improving the kinetics of electrochemical reactions. Ceria-based oxides have applications in solid oxide fuel/electrolysis cells, thermo-chemical water splitting, catalytic convertors, and red-ox active memristive devices. The surface defect chemistry of doped ceria in the regime of high oxygen pressure, <i>p</i>O₂, approximating the operating conditions of fuel cell cathodes at elevated temperatures, has not yet been revealed. In this work, we investigated the Pr_0.1Ce_0.9O_2−δ (PCO) surface by <i>in operando</i> X-ray photoelectron and absorption spectroscopic methods. We quantified the concentration of reduced Pr³⁺, at the near-surface region of PCO as a function of electrochemical potential, corresponding to a wide range of effective <i>p</i>O₂. We found that the Pr³⁺ concentration at the surface was significantly higher than the values predicted from bulk defect chemistry. This finding indicates a lower effective defect formation energy at the surface region compared with that in the bulk. In addition, the Pr³⁺ concentration has a weaker dependence on <i>p</i>O₂ compared to that in the bulk