2,006 research outputs found
Nitrogen loss and oxygen evolution reaction activity of perovskite oxynitrides
Perovskite oxynitride photocatalysts were reported by experiment to evolve
small amounts of N due to the self-oxidation of nitrogen ions by
photo-generated holes. The N evolution rate was observed to decrease with
increasing reaction time and was found to be correlated with a decrease in
O evolution (OER) activity, the origin of this latter effect however being
unknown. Here we investigate, by means of density functional theory
calculation, anion vacancies at the TaON-terminated (001) surface of the
perovskite oxynitride SrTaON. We find an energetic preference for oxygen
and nitrogen vacancies to reside at the surface, where they are spontaneously
healed by *O and *OH adsorbates under OER conditions. For nitrogen vacancies,
this self-healing leads to an altered stoichiometry TaON
that is accompanied by electron doping. Substitution of N by O at the surface
also leads to tensile strain, which confines the excess charge to the very
surface layer, affecting the binding energy of reaction intermediates and
significantly increasing the OER overpotential. This peculiar change in
electronic structure thus provides an atomic scale explanation for the
experimentally observed drop in OER activity of perovskite oxynitrides.Comment: 15 pages, 7 figure
"How Should the Surpluses Be Spent?"
What are the likely economic consequences, particularly on saving, investment, and long-term economic growth, of three alternative uses of budget surpluses: paying down the debt, increasing government spending, and cutting taxes?
Band-gap engineering in AB(OS) perovskite oxysulfides: A route to strongly polar materials for photocatalytic water splitting
Polar heterogeneous photocatalysts were shown to lead to enhanced
charge-carrier separation that results in superior activity for example for
photocatalytic water splitting. Promising photocatalyst materials such as
oxynitrides can be rendered polar by epitaxial strain, which however also
increases their band gap, making them unsuitable for visible light absorption.
This suggests a trade-off between small band gaps and polar distortions - both
being crucial for the catalyst's efficiency. In this paper we investigate,
using density functional theory calculations, the suitability of strained
AB(OS) perovskites for photocatalytic water splitting. These
materials normally have band gaps too small for water splitting but inducing
polar distortions via epitaxial strain can increase the band gap to the
suitable range. We find perovskite BaZrTiOS compounds to be
highly promising for photocatalytic water splitting due to large polar
distortions and suitable band gaps.Comment: 7 pages, 8 figure
"How Big Should the Public Capital Stock Be? The Relationship Between Public Capital and Economic Growth"
Investment in infrastructure is necessary for a strong, flexible, and growing economy. However, the relationship between public capital and economic growth is not linear. At a certain level, the tax burden associated with financing and maintaining public capital reduces the returns to private industry, which, in turn, reduces growth; also, different types of spending have different effects on growth. The short- and long-term growth-maximizing effects of public investment increase as the ratio of public to private capital stock rises to an optimal level (found to be about 61 percent); above that level the growth effects decrease. The public to private ratio is below the optimal level throughout much of the country and government spending is not always directed toward the types of investment that have the most positive effects on growth. Good economic policy requires both increasing the public capital stock and reorienting government spending from consumption to investment in physical capital stock.
The Role of Public Infrastructure Capital in Mexican Economic Growth
This paper develops and empirically implements a neoclassical growth model in which output depends on private capital and human capital as well as the quantity, means of financing, and efficiency of use of public capital. The empirical analysis is based on a cross section of 46 developing countries over the period from 1970 to 1990. In general, the paper finds empirical support for the importance of each of the three dimensions of public capital –quantity, financing, and efficiency– for long run standards of living and for transitional growth rates. The empirical results are applied to the recent performance of the Mexican economy.
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