Carbon-supported PtM nanostructured materials (M = Cr, Co, Ni, Cu, Mo, Y, Sm, Gd) were investigated for the hydrogen evolution/oxidation reactions (HER/HOR) in alkaline medium. All catalysts were ...synthesized by the carbonyl complex chemical route. Among PtM, Cr, Co, Ni, and Cu formed nanoalloys. M
2
O
3
was generated with Y, Sm, and Gd, and Mo was found at a dopant concentration of Pt. The electrochemical results showed that the HER/HOR activities on PtNi/C and PtCo/C outperformed that of the Pt/C benchmark. The presence of OH
ads
species, acting as a bifunctional mechanism, favored the HER/HOR activity on PtNi/C and PtCo/C. This process is concomitant with early DFT studies that concluded that the presence of OH
ads
weakens the H
ads
and H
2
O
ads
energetics.
Graphical abstract
Many advances in artificial intelligence and machine learning are based on decision making, especially in uncertain settings. Due to its possible applications, decision making is currently a broad ...field of study in many areas like Computation, Economics and Business Management. The first techniques appeared in scenarios where information was modeled by real numbers. In all cases, one of the key steps in such processes was the summarization of the available information into a few values that helped the decision maker to complete this task. In this paper, we introduce a novel multi-criteria decision making methodology in the fuzzy context in which weights and experts’ opinions (may be translated by linguistic labels) are stated as triangular fuzzy numbers. To do that, we take advantage of a recently presented fuzzy binary relation whose properties are according to human intuition and we carry out a study of the main properties that an aggregation function (a mapping to sum up information) must satisfy in the fuzzy framework. The presented procedure makes a final decision based on parabolic fuzzy numbers (not triangular). And this will be shown in an illustrative example.
In this paper we propose a notion of coincidence point between mappings in any number of variables and we prove some existence and uniqueness fixed point theorems for nonlinear mappings verifying ...different kinds of contractive conditions and defined on partially ordered metric spaces. These theorems extend and clarify very recent results that can be found in T. Gnana-Bhaskar, V. Lakshmikantham, Fixed point theorems in partially ordered metric spaces and applications, Nonlinear Anal. 65 (7)(2006) 1379–1393, V. Berinde, M. Borcut, Tripled fixed point theorems for contractive type mappings in partially ordered metric spaces, Nonlinear Anal. 74 (2011) 4889–4897 and M. Berzig, B. Samet, An extension of coupled fixed point’s concept in higher dimension and applications, Comput. Math. Appl. 63 (8) (2012) 1319–1334.
Different sources of imprecision and uncertainty are encountered in practical problems and, thus, many elements may need to be imprecisely observed, defined or treated. In this setting, one of the ...most successfully applied techniques to describe possible relationships between fuzzy variables is the regression methodology. In this paper, we introduce a fuzzy regression procedure involving a class a fuzzy numbers defined by some level sets called finite fuzzy numbers. We give a characterization of the image of a finite fuzzy number in terms of the extremes of its level sets and we present a parametric family of fuzzy semidistances between them that let us to consider a total fuzzy error of estimation (described as a fuzzy sum of squares of residuals in particular cases). The estimation process consists in finding a regression model that minimizes, in a fuzzy sense, such fuzzy error. Although spreads of finite fuzzy numbers can take some values very close to zero, which complicate the task of finding nonnegative models, the presented algorithm is able to guarantee that the predicted response is a fuzzy variable. Finally a numerical example based on fuzzy economic data of China is given to illustrate the use of the proposed method.
We study the existence and uniqueness of coincidence point for nonlinear mappings of any number of arguments under a weak (ψ, φ)-contractivity condition in partial metric spaces. The results we ...obtain generalize, extend, and unify several classical and very recent related results in the literature in metric spaces (see Aydi et al. (2011), Berinde and Borcut (2011), Gnana Bhaskar and Lakshmikantham (2006), Berzig and Samet (2012), Borcut and Berinde (2012), Choudhury et al. (2011), Karapınar and Luong (2012), Lakshmikantham and Ćirić (2009), Luong and Thuan (2011), and Roldán et al. (2012)) and in partial metric spaces (see Shatanawi et al. (2012)).
Despite the impressive photovoltaic performances with power conversion efficiency beyond 22%, perovskite solar cells are poorly stable under operation, failing by far the market requirements. Various ...technological approaches have been proposed to overcome the instability problem, which, while delivering appreciable incremental improvements, are still far from a market-proof solution. Here we show one-year stable perovskite devices by engineering an ultra-stable 2D/3D (HOOC(CH
)
NH
)
PbI
/CH
NH
PbI
perovskite junction. The 2D/3D forms an exceptional gradually-organized multi-dimensional interface that yields up to 12.9% efficiency in a carbon-based architecture, and 14.6% in standard mesoporous solar cells. To demonstrate the up-scale potential of our technology, we fabricate 10 × 10 cm
solar modules by a fully printable industrial-scale process, delivering 11.2% efficiency stable for >10,000 h with zero loss in performances measured under controlled standard conditions. This innovative stable and low-cost architecture will enable the timely commercialization of perovskite solar cells.
Characterization and electrochemical evaluation of novel metal-free electrocatalysts obtained by solar pyrolysis is reported. Carbon-based electrocatalysts were prepared from agave bagasse waste, ...using a sustainable process based on concentrated solar energy as heat source. Agave was processed in a spherical borosilicate glass solar reactor using a heating rate of 30 °C min−1 to a target of 500, 700, or 900 °C, and maintaining temperature for 1 h under inert atmosphere. The structure and composition of the prepared electrocatalysts were influenced by pyrolysis temperature. In addition, electrocatalytic activity towards the oxygen reduction reaction in 0.1 M KOH solution was explored. The electrocatalyst obtained at 500 °C showed the highest activity among all pyrolyzed samples due to its moderate surface area, but mostly due to its higher oxygen content. The metal-free electrocatalysts reported in this work are promising eco-friendly alternative as cathode materials for anion-exchange membrane fuel cells. This study provides a sustainable approach to use agricultural biomass waste to produce valuable materials for electrochemical energy devices.
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•Sustainable approach to produce alternative cathodic material for AEMFC.•Biomass-derived electrocatalysts were prepared by solar pyrolysis.•Agave bagasse is a good raw material for metal-free electrocatalysts synthesis.•Electrocatalyst synthesized at 500 °C showed the highest activity.
The activity/stability towards the ORR of Pt
x
Gd/C nanoalloys has been enhanced by controlling the atmosphere during the dealloying process. By minimising the formation of porous nanoarchitectures, ...the ORR activity is increased, and is accompanied by higher activity retention and attenuation of metal dissolution on cycling to high voltage.
The activity/stability towards the ORR of Pt
x
Gd/C nanoalloys has been enhanced by controlling the atmosphere during the dealloying process.
Advances in nanoscale magnetism increasingly require characterization tools providing detailed descriptions of magnetic configurations. Magnetic transmission X-ray microscopy produces element ...specific magnetic domain images with nanometric lateral resolution in films up to ∼100 nm thick. Here we present an imaging method using the angular dependence of magnetic contrast in a series of high resolution transmission X-ray microscopy images to obtain quantitative descriptions of the magnetization (canting angles relative to surface normal and sense). This method is applied to 55-120 nm thick ferromagnetic NdCo5 layers (canting angles between 65° and 22°), and to a NdCo5 film covered with permalloy. Interestingly, permalloy induces a 43° rotation of Co magnetization towards surface normal. Our method allows identifying complex topological defects (merons or ½ skyrmions) in a NdCo5 film that are only partially replicated by the permalloy overlayer. These results open possibilities for the characterization of deeply buried magnetic topological defects, nanostructures and devices.
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