Display omitted
•Perovskites with Mn and Fe as B cation successfully prepared and tested in STS.•Mixed materials show structural features intermediate between pure Mn and Fe perovskites.•The presence ...of Fe improves self-reduction and, therefore, the producible H2.•The presence of Mn improves the oxidation kinetics, lowering typical splitting temperature.•Use of diverse B ions as an effective strategy to manage self-reducibility and splitting activity.
Mixed perovskites, described by the formula La0.6Sr0.4Mn1−xFexO3−δ with x ranging from 0 to 1, were prepared and tested as potential catalysts for the solar thermochemical water and carbon dioxide splitting. The increase of iron amount promotes the reduction step according to the trend of the starting reduction temperatures; on the other hand, the reactivity towards H2O and CO2 seems to be fostered by high Mn contents. The highest amounts of oxygen evolved during thermogravimetric analysis and hydrogen produced during splitting tests occur to the sample with x = 1 even if a non-monotonic trend with iron substitution is appreciated. Instead, CO amount progressively decreases by increasing iron content. The results reported in this work indicate that the formulation of bi-functional systems with two active sites, one showing good self-reduction the other good reactivity towards splitting reactions, is the best route to prepare materials with larger intrinsic H2 and CO productivity as well as lower reduction/oxidation temperature.
By making use of a recently proposed framework for the inference of thermodynamic irreversibility in bosonic quantum systems, we experimentally measure and characterize the entropy production rates ...in the nonequilibrium steady state of two different physical systems-a micromechanical resonator and a Bose-Einstein condensate-each coupled to a high finesse cavity and hence also subject to optical loss. Key features of our setups, such as the cooling of the mechanical resonator and signatures of a structural quantum phase transition in the condensate, are reflected in the entropy production rates. Our work demonstrates the possibility to explore irreversibility in driven mesoscopic quantum systems and paves the way to a systematic experimental assessment of entropy production beyond the microscopic limit.
The use of magnetic nanoparticles for magnetic hyperthermia cancer treatment is a rapidly developing field of multidisciplinary research. From the material's standpoint, the main challenge is to ...optimize the heating properties of the material while maintaining the frequency of the exciting field as low as possible to avoid biological side effects. The figure of merit in this context is the specific absorption rate (SAR), which is usually measured from calorimetric experiments. Such measurements, which we refer to as heating curves, contain a substantial amount of information regarding the energy barrier distribution of the sample. This follows because the SAR itself is a function of temperature, and reflect the underlying magneto-thermal properties of the system. Unfortunately, however, this aspect of the problem is seldom explored and, commonly, only the SAR at ambient temperature is extracted from the heating curve. In this paper we introduce a simple model capable of describing the entire heating curve via a single differential equation. The SAR enters as a forcing term, thus facilitating the use of different models for it. We discuss in detail the heating in the context of Néel relaxation and show that high anisotropy samples may present an inflection point related to the reduction of the energy barrier caused by the increase in temperature. Mono-disperse and poli-disperse systems are discussed in detail and a new alternative to compute the temperature dependence of the SAR from the heating curve is presented.
► A theoretical model for the heating curve in magnetic hyperthermia is developed. ► The specific absorption rate enters as a simple forcing term, facilitating the use of different models to describe it. ► We analyze in detail heating curves for particle with Néel relaxation. ► It is shown that the appearance of an inflection point in the heating curve is a direct consequence of high anisotropy samples. ► A new method to extract the temperature dependence of the SAR from the heating curve is proposed.
A CuO/CeO2 catalyst with 4 wt % CuO nominal content has been prepared by solution combustion synthesis (SCS) and characterized by ICP-MS, BET surface area analysis, XPS, HRTEM, and H2, and/or CO TPR. ...The catalyst, showing a rather homogeneous distribution of copper that strongly interacts with ceria, has been tested in CO-PROX reaction. The enhanced performance of the catalyst compared to that of an impregnated sample with the same copper loading has been explained by modeling the experimental CO2 temperature-programmed desorption (TPD) curve, which allowed the determination and quantification of different active sites. The temperature range of activity and the ratio of the amount of sites activating CO and H2 oxidation, respectively, estimated for the two catalysts through the model explain the superior performance of the sample prepared by SCS despite its lower surface area.
•Influence of a degraded triple junction solar cell on a CPV system.•Experimental characterization of the triple junction cell after the aging process.•Comparison of the CPV energy performances ...between the pristine and aged states.
A concentrating photovoltaic (CPV) plant is a complex system that integrates different technologies as single or multi-junction photovoltaic cells and optical devices. The CPV system performance analysis should take into account the malfunctions that can occur during the working, especially when the system operates with high values of sunlight concentration. A critical analysis of the solar cells is necessary to define the CPV system potential. In this paper a specific configuration of a CPV system is considered, and the experimental analysis of a system with a degraded triple-junction InGaP/GaAs/Ge solar cell is investigated. In particular, the triple-junction solar cell is stressed in an accelerated aging process of about 500 operating hours with a concentration of 310 suns without using a cooling system. After this process, for another 100 working hours the system has been monitored in order to compare, corresponding to different light concentration factors, the solar cell electric characteristics, the energy production and the power conversion efficiency in the pristine and degraded states. The results show the effect of the overheating of the triple-junction solar cell caused by the excessive increase of the light intensity. Under the same irradiance of 930 W/m2 the short circuit current, open circuit voltage and fill factor values of the aged solar cell, compared to the pristine device, result to be strongly reduced, while the extracted value of the series resistance increases and the values of the shunt resistances decrease. The increased value of the diode ideality factor m after the thermal stress indicates a non-negligible contribution of non-radiative recombination within the solar cell. Similar findings are deduced comparing the electroluminescence spectra of the pristine and degraded solar cell. The thermal stress induces a marked drop of electroluminescence signal intensity in the whole investigated wavelength range. It should be note that high electroluminescence efficiency is a good indicator in solar cells for high power conversion efficiencies. In particular, the power conversion efficiency is reduced by 50% referring to a CPV system with a degraded cell, while the electric output power is decreased by 30%. Hence, it is clear that the triple-junction cell inefficiencies, principally caused by a strong thermal stress, lead to a drastic drop of the CPV system performances. Finally, an active cooling system is absolutely necessary when high values of light concentration are reached.
A theoretical model, combining trapping/detrapping and recombination mechanisms, is formulated to explain the origin of random current fluctuations in silicon-based solar cells. In this framework, ...the comparison between dark and photo-induced noise allows the determination of important electronic parameters of the defect states. A detailed analysis of the electric noise, at different temperatures and for different illumination levels, is reported for crystalline silicon-based solar cells, in the pristine form and after artificial degradation with high energy protons. The evolution of the dominating defect properties is studied through noise spectroscopy.
•Experimental characterization of a concentrating photovoltaic system.•Analysis of the point-focus concentrating system performances.•Photovoltaic system parameters as function of the concentration ...factor.
The concentrating photovoltaic system represents one of the most promising solar technologies because it allows a more efficient energy conversion. When a CPV system is designed, the main parameter which has to be considered is the concentration factor that affects both the system energy performances and its configuration. An experimental characterization of a CPV system previously realized at the University of Salerno, is presented in this paper considering several aspects related to the optical configuration, the concentration factor and the solar cell used. In particular, the parameters of an Indium Gallium Phosphide/Gallium Arsenide/Germanium triple-junction solar cell are investigated as function of the concentration factor determined by means of an experimental procedure that uses different optical configurations. The maximum concentration factor reached by the CPV system is 310 suns. The cell parameters dependence on the concentration is reported together with an electroluminescence analysis of the Indium Gallium Phosphide/Gallium Arsenide/Germanium cell. A monitoring of the electrical power provided by the system during its working is also presented corresponding to different direct irradiance values. A mean power of 2.95W with an average efficiency of 32.8% is obtained referring to a mean irradiance of 930W/m2; lower values are obtained when the irradiance is highly fluctuating. The concentrating photovoltaic system electric energy output is estimated considering different concentration levels; the maximal obtained value is 23.5Wh on a sunny day at 310×. Finally, the temperature of the triple-junction solar cell is evaluated for different months in order to evaluate the potential annual thermal energy production of the concentrating photovoltaic system.
PDF
