Although conventional cogeneration systems have been used successfully in the last two decades, most of them have been large units using mainly hydrocarbon fuels that are becoming increasingly ...expensive. New cogeneration systems based on fuel cells and sorption air conditioning systems promise to be an energy-saving alternative for situations when cooling, heating and power are needed at low and medium capacities. Cogeneration Fuel Cell-Sorption Air Conditioning Systems examines the thermodynamic principles of fuel cell performance and sorption air conditioning systems, and gives relevant information about the state of the art of these technologies. It also provides the reader with the theoretical bases and knowledge needed to understand the operation of these new cogeneration systems, as well as discussing the design basis and economical evaluation. Topics covered include: selected fuel cells for cogeneration CHP processes, state-of-the-art sorption refrigeration systems, potential applications in demonstration projects, and profitability assessment of the cogeneration system. Air conditioning and fuel cell engineers, postgraduates and researchers in energy fields, and designers of cooling, heating and power cogeneration systems will find Cogeneration Fuel Cell-Sorption Air Conditioning Systems a useful and informative reference.
The influence of predominant native defects in forming ZnO with p-type conductivity is discussed in this work when the semiconductor is synthesized only in water. The semiconductor was prepared by ...dissolving a Zn-salt in deionized water at 80 °C. The powders were thermally treated at 400 °C in an air atmosphere to obtain well-defined crystalline ZnO. XRD, SEM, EDS, Raman spectroscopy, diffuse reflectance, photoluminescence, and Seebeck effect techniques were used to characterize the synthesized material. The results showed a well-crystalline semiconductor in wurtzite phase. The crystal-oriented growth was the (002) plane. The sample morphology was formed by highly ordered sticks-like. The optoelectronic characterization showed that the synthesized ZnO had a lower band gap than that reported in the literature. It was related to deep energy levels corresponding to oxygen interstitials as the predominant native defects. Raman, EPR, and photoluminescence spectra analysis corroborated the existence of native defects in the crystalline structure. The p-type conductivity of the sample was determined by Seebeck coefficient analysis. A synthesis reaction mechanism involving the formation of oxygen interstitials was proposed in this work. Understanding the effects of native defects in wide band gap semiconductors is necessary to design new materials for sensors or energy conversion applications.
•Crystalline ZnO samples were prepared using three concentrations of parsley extract.•The conductivity type of ZnO depends on the concentration of parsley extract.•Mg traces were incorporated into ...the ZnO matrix during the synthesis.•ZnO with less than 2 at% of Mg showed p-type conductivity.•Oxygen interstitials and oxygen vacancies are affected by the synthesis and the annealing process.
ZnO samples were prepared by an easy process based on green synthesis using three different concentrations of the parsley extract as natural reducing agents. The semiconductors were characterized structural, morphological, and opto-electronically by XRD, SEM-EDS, diffuse reflectance, and photo-response, respectively. Hexagonal structure ZnO-based semiconductors were obtained after the annealing process at 400ºC. The morphology, bandgap, and photo-response of the synthesized samples were sensitive to the extract concentrations used in this work. The incorporation of Mg traces in the bulk of ZnO produced changes in the c-lattice parameter, consequently forming native defects such as Oi and Vo. The bandgap increased as the Mg content in the ZnO increased too. The photo-response analysis suggested that the samples with 0.44 and 1.33 at% of Mg were p-type ZnO, while the sample with 2.01 at% was n-type ZnO. It likely means that the conductivity type and other optoelectronic characteristics depend on the Mg content in the ZnO samples and the formation of predominant native defects due to the interaction of Mg with the crystalline structure.
Abordagem filosófica, histórica e política, dos conceitos de Liberalismo, de Neoliberalismo e de Pós-Modernidade. Analisa os contextos históricos e as premissas ontológicas e epistemológicas da ...Modernidade e das projeções mais comuns na abordagem Pós-Moderna. Estudo descritivo e aproximativo, sob o enfoque histórico-crítico, de concepções de mundo e de conhecimento. Debate as causalidades da eclosão do projeto Neoliberal e suas articulações políticas e sociais. Aponta as contradições do enfoque pós-moderno de abordagem teórico-metodológica e questiona sua possibilidade de superação das causalidades reais. Interpreta as repercussões do Neoliberalismo e da metodologia Pós-Moderna na Pesquisa em Educação.
ZnO was obtained by reducing Zn salt in parsley extract at 80 °C. Structural and morphological characteristics of ZnO obtained by green synthesis were compared with ZnO acquired commercially and ZnO ...synthesized by simple water reduction. XRD and EDS suggested the presence of Mg traces in the ZnO synthesized in parsley extract. In this case, the incorporation of Mg in the crystalline structure of Zn-O was investigated by analyzing the changes in the c-parameter of the wurtzite structure. The analysis by SEM showed a well-defined hexagonal morphology of particles. Raman Spectroscopy was used to measure the optical and longitudinal vibrations of ZnO:Mg. The calculated band gap for ZnO:Mg was lower than commercial ZnO. The decrease in the band gap energy was attributed to the presence of atomic Mg in the ZnO lattice. The photoluminescence activity of ZnO:Mg was mainly observed at the UV, blue and green regions.
•➢ZnO synthesized in parsley extract at 80 °C shows hexagonal morphology.•➢Parsley extract plays an important role during the synthesis of crystalline ZnO.•➢ZnO synthesized in parsley extract incorporates Mg in the ZnO matrix.•➢ZnO obtained by green synthesis shows a band gap lower than commercial ZnO.
In this study, the electro-oxidation reaction of ethanol over Pd–Cu supported on Cu porphyrin (TPPCu) was investigated. The catalyst was synthesized using the microwave-assisted polyol method and ...physicochemically characterized by XRD, XPS, SEM, EDS, TEM, EDAX, UV–Vis, FTIR, and RBS. A Cu-enriched catalyst with Cu
3
Pd, Pd,Cu, and TPPCu phases was identified using XRD and XPS. However, according to the RBS results, the catalytic surface was enriched with Pd, indicating that the interaction between TPPCu and Pd–Cu allowed the presence of Pd on the surface, thus enhancing the catalytic response of the material. This synthesis prevented the deprotonation of porphyrin on the electrocatalyst, as confirmed by XPS analysis. Electrochemical studies based on cyclic voltammetry and electrochemical impedance spectroscopy were used to investigate the response of the catalyst to variations in the scan rate and increasing ethanol concentration. The electrochemical response of PdCu/TPPCu improved with an increasing number of cycles, indicating improved mass transport, thus improving its electrochemical response and tolerance to CO contamination. This catalyst exhibited a high electroactive surface area of 49.4 m
2
/g, which could be related to the presence of TPPCu as a support. The behavior of the catalyst on the anode of a fuel cell fed with ethanol, bioethanol, and bioethanol residues was evaluated.
Graphical Abstract
The initial stage of the hydrogen absorption/desorption process in ceramic electrodes is discussed in this work. The experiments were carried out at 25 °C in a concentrated alkaline medium. The ...electrodes were prepared using LaB6 and LaBO3. Pd nanoparticles were incorporated into the electrodes to activate them electrochemically. The results showed that the electrodes could absorb hydrogen electrochemically at room temperature. The LaBO3 electrode showed better hydrogen absorption characteristics than LaB6. The morphological and volumetric properties were crucial in achieving the hydrogen storage in the electrode. The discharge capacity was similar in both electrodes. However, the LaBO3 electrode supplied more energy than the LaB6-based electrode. The charge absorption reaction prevailed in both electrodes instead of the hydrogen evolution reaction. The capability of the ceramic electrodes to absorb/desorb hydrogen electrochemically is controlled by the diffusion processes that occur at the electrode/electrolyte interface and the crystalline planes of the ceramic materials.
•LaBO3 powders were synthesized by combustion method.•Ceramic electrodes were fabricated using synthesized LaBO3 and commercial LaB6.•Pd/C activated the ceramic electrodes.•Electrochemical techniques evaluated the hydrogen absorption in ceramic electrodes.•Ceramic hydrides absorbed and desorbed energy electrochemically.
La cirugía, sin duda alguna, ha jugado un papel fundamental en la evolución de la medicina moderna: por medio de sus avances, la calidad de los tratamientos médicos ha mejorado de manera ...trascendental la expectativa de vida de muchas patologías. Algunos autores afirman que sus inicios se remontan a la época de la prehistoria, cuando tribus indígenas ya realizaban procedimientos quirúrgicos como amputaciones, litotomías, ablación de cataratas y trepanaciones de cráneos, entre otros. Sin embargo, su punto de inflexión se marco hace aproximadamente 150 años con el descubrimiento de la anestesia y la posterior aparición del uso de antibióticos.
Platinum colloidal nanoparticles were synthesized by chemical reduction of metallic salts in presence of poly (N-vinyl-2-pirrolidone) which served as a protecting agent. The preparation conditions ...for obtaining Pt nanoparticles were established by analyzing TEM and HRTEM images of the samples. Size of the synthesized Pt nanoparticles was in the range 2.5 to 8.5
nm depending on the molarity of PtCl
4 used to prepare the colloidal dispersion. The electrochemical characteristics of the Pt nanoparticles supported on carbon were investigated by analyzing their catalytic response to the oxygen reduction reaction (ORR). The reactivity of the prepared catalyst was comparable to that of the commercially available carbon supported Pt for the ORR. Catalytic parameters like charge transfer coefficient, Tafel constants and exchange current density were calculated for the prepared catalyst.
A photoelectrochemical study of Cu(In
,Ga)Se
2 (CIGS) thin films in 0.5
M H
2SO
4 is presented in this work. CIGS thin films were obtained by electrodeposition of CuInSe
2 (CIS) and the composition ...was adjusted by physical vapor deposition (PVD) to obtain CuIn
1−
x
Ga
x
Se
2. Photo-electrodes were prepared using CIGS thin films. These electrodes exhibited cathodic photoresponse associated with the hydrogen evolution occurring at 0.3
V more positive potential than the potential observed for the hydrogen evolution in the dark. The production of hydrogen by CIGS films at different potentials was estimated by coulometric measurements, showing that under illumination the quantity of hydrogen produced was two orders of magnitude higher than the hydrogen produced in the dark.
PDF
