RESUMEN
Chalcopyrite CuInSe2 (CISe)-based thin-film photovoltaic solar cells have been attracting attention since the 1970s. The technologies of CISe-based thin-film growth and device fabrication processes have already been put into practical applications and today commercial products are available. Nevertheless, there are numerous poorly understood areas in the physical and chemical aspects of the underlying materials science and interfacial and bulk defect physics in CISe-based thin-films and devices for further developments. In this paper, current issues in physical and chemical studies of CISe-based materials and devices are reviewed. Correlations between Cu-deficient phases and the effects of alkali-metals, applications to lightweight and flexible solar minimodules, single-crystalline epitaxial Cu(In,Ga)Se2 films and devices, differences between Cu(In,Ga)Se2 and Ag(In,Ga)Se2 materials, wide-gap CuGaSe2 films and devices, all-dry processed CISe-based solar cells with high photovoltaic efficiencies, and also fundamental studies on open circuit voltage loss analysis and the energy band structure at the interface are among the main areas of discussion in this review.
RESUMEN
This study proves that a small amount of Pd loading (1 wt%) on Sr3Fe2O7-δ can dramatically enhance the oxygen-storage properties of Sr3Fe2O7-δ. The topotactic oxygen intake and release between Sr3Fe2O6.75 and Sr3Fe2O6 takes place in response to gas switching between an O2 flow and H2 flow, regardless of the presence or absence of Pd loading. The effect of Pd loading is significant for the oxygen-release process under H2 atmosphere; that is, highly dispersed Pd metal nanoparticles sized less than 1 nm formed on Pd/Sr3Fe2O7-δ to promote H2 dissociation, resulting in the improvement of the oxygen-release temperature and rate. Pd/Sr3Fe2O7-δ with a layered perovskite structure has a higher oxygen-release property at lower temperature than Pd/SrFeO3-δ with a perovskite phase without the layered structure. These facts indicate that the surface reaction as well as the crystal structure are responsible for the oxide ion mobility in perovskite structure, and also provide guidelines for designing novel oxygen-storage materials.
RESUMEN
A Pd3Bi intermetallic compound (IMC) was photocatalytically deposited onto the gallium oxide (Ga2O3) surface at room temperature. Conventional impregnation and reduction methods were difficult for the formation of the Pd3Bi IMC on Ga2O3, highlighting the importance of the photodeposition approach. The Pd3Bi-loaded Ga2O3 photocatalyst exhibited 84% selectivity in methane-to-ethane conversion with hydrogen production in the presence of water vapour.
RESUMEN
Determination of a reaction pathway is an important issue for the optimization of reactions. However, reactions in solid-state compounds have remained poorly understood because of their complexity and technical limitations. Here, using state-of-the-art high-speed time-resolved synchrotron X-ray techniques, the topochemical solid-gas reduction mechanisms in layered perovskite Sr3 Fe2 O7- δ (from δ ⼠0.4 to δ = 1.0), which is promising for an environmental catalyst material is revealed. Pristine Sr3 Fe2 O7- δ shows a gradual single-phase structural evolution during reduction, indicating that the reaction continuously proceeds through thermodynamically stable phases. In contrast, a nonequilibrium dynamically-disordered phase emerges a few seconds before a first-order transition during the reduction of a Pd-loaded sample. This drastic change in the reaction pathway can be explained by a change in the rate-determining step. The synchrotron X-ray technique can be applied to various solid-gas reactions and provides an opportunity for gaining a better understanding and optimizing reactions in solid-state compounds.
RESUMEN
Environmental catalysts are required to operate highly efficiently under severe conditions in which they are exposed to reductive and oxidative atmospheres at high temperatures. This study demonstrates that SrFe1- xTi xO3-δ-supported Pd catalysts exhibit high catalytic activities for NO reduction with C3H6 and CO in the presence of O2, which is a model reaction for the purification of automotive exhaust gases. Catalytic activity is enhanced with increasing Ti content, and the highest activity is observed for Pd/SrFe0.2Ti0.8O3-δ among the examined catalysts. The state of the loaded Pd species can be controlled by the Fe/(Fe + Ti) ratio in SrFe1- xTi xO3-δ, and highly active PdO nanoparticles are properly anchored on SrFe0.2Ti0.8O3-δ. The Ti-rich Pd/SrFe0.2Ti0.8O3-δ shows significantly higher catalytic activity and is more thermally stable than the conventional Pd/Al2O3, which has a high surface area. Since Fe-rich SrFe1- xTi xO3-δ has the high oxygen storage capacity, its response capabilities to atmospheric fluctuations were evaluated by changing the oxygen concentration during NO reduction. As a result, Fe-rich Pd/SrFe0.8Ti0.2O3-δ retains its high NO-reduction activity for longer times even under oxidative conditions, when compared to SrFeO3-δ or Ti-rich Pd/SrFe1- xTi xO3-δ. The oxygen storage properties of Pd/SrFe0.8Ti0.2O3-δ allow it to effectively act as an oxygen buffer for NO reduction. These properties ensure that the SrFe1- xTi xO3-δ support, with both high thermal stability and oxygen storage capacity, is a very useful environmental-catalyst material.