1,720,972 research outputs found
Highly efficient and stable spray assisted nanostructured Cu2S/Carbon paper counter electrode for quantum dots sensitized solar cells
Get PDFThe counter electrode (CE) plays a significant role in determining the overall performance and long-term stability of quantum dots (QDs) sensitized solar cells (QDSCs) by collecting the electrons from the external circuit and catalyzing the regeneration of the oxidized electrolyte. In this work, we report a simple, low cost and large area scalable spray deposition approach to fabricate nanostructured Cu2S CE on a carbon fiber paper (CP). The QDSCs were assembled with optimized spray assisted nanostructured Cu2S/CP CEs, and yield a photoconversion efficiency (PCE) of 5.06%, which is 28% higher than QDSCs based on Cu2S/Brass CEs. The PCE can be further boosted to 5.89% upon optimization of the photoanode structure. In addition, QDSCs with Cu2S/CP CEs exhibit better long-term stability than QDSCs with Cu2S/Brass CE. This excellent performance and satisfactory long-term stability of QDSCs with Cu2S/CP CEs is mainly attributed to the synergistic effect of excellent conductivity of CP and high and stable catalytic activity of nanostructured Cu2S, which is confirmed by cyclic voltammetry and electrochemical impedance spectroscopy. Thus, our results define a cost-effective and large area scalable approach to fabricate highly efficient and stable CEs, which is an important step toward the fabrication of solar driven optoelectronic devices
A colloidal heterostructured quantum dot sensitized carbon nanotube-TiO 2 hybrid photoanode for high efficiency hydrogen generation
Get PDFSolar-driven photoelectrochemical (PEC) hydrogen (H 2 ) generation is a promising approach to harvest solar energy for the production of a clean chemical fuel. However, the low photon-to-fuel conversion efficiency and long-term stability of PEC devices are major challenges to be addressed to enable large-scale commercialization. Here we report a simple, fast and cost-effective approach to fabricate high efficiency and stable PEC devices for H 2 generation, by fabricating a hybrid photoanode obtained by incorporating small amounts of multiwall carbon nanotubes (MWCNTs) into a TiO 2 mesoporous film and sensitizing with colloidal heterostructured CdSe/(CdSe x S 1-x ) 5 /(CdS) 2 quantum dots (QDs). The latter were specially designed to accelerate the exciton separation through a band engineering approach. The PEC devices based on the TiO 2 /QD-MWCNT (T/Q-M) hybrid photoanode with an optimized amount of MWCNTs (0.015 wt%) yield a saturated photocurrent density of 15.90 mA cm -2 (at 1.0 V RHE ) under one sun illumination (AM 1.5G, 100 mW cm -2 ), which is 40% higher than that of the reference device based on TiO 2 /QD (T/Q) photoanodes. This is attributed to a synergistic effect of the promising optoelectronic properties of the colloidal heterostructured QDs and improved electron transport (reduced charge transfer resistance) within the TiO 2 -MWCNT hybrid anodes enabled by the directional path of MWCNTs for the photo-injected electrons towards FTO. Furthermore, the PEC device based on the T/Q-M hybrid photoanode is more stable (∼19% loss of its initial photocurrent density) when compared with the T/Q photoanode (∼35% loss) after two hours of continuous one sun illumination. Our results provide fundamental insights and a different approach to improve the efficiency and long-term stability of PEC devices and represent an essential step towards the commercialization of this emerging solar-to-fuel conversion technology
Enhanced Photocurrent Generation in Proton-Irradiated “Giant” CdSe/CdS Core/Shell Quantum Dots
Get PDFGroup II–VI quantum dots (QDs) possess tunable electrical and optical properties that make them very attractive for high-tech applications and power generation. The effects of proton irradiation on both the structural and physical properties of “giant” CdSe/CdS core–shell QDs (g-CS QDs) are investigated. These experiments shed light on photoelectron delocalization in g-CS QDs, where current linkages and strong variations in optical emission result from the spatial extension of the photoelectron wavefunctions over the conduction bands of CdSe and CdS. Monte Carlo simulations of ion–matter interactions show that the damaging rates can be set from the energy of impinging protons to promote the formation of structural defects in the core or shell. The formation of nanocavities is demonstrated after irradiation doses higher than ≈1017 H+ cm−2, while a continuous decrease in luminescence intensity is observed for increasing proton fluencies. This feature is accompanied by a concomitant lifetime decrease marking the rise of nonradiative phenomena and the occurrence of greater photocarrier transfers between CdS and CdSe. Current-to-voltage characterizations evidence that proton implantation can be implemented to enhance the photocurrent generation in g-CS QDs. This increase is attributed to the delocalization of photoelectrons in the CdS shell, whose improvement is found to promote electron–hole pair separation
Graphene nanoribbon-TiO2-quantum dots hybrid photoanode to boost the performance of photoelectrochemical for hydrogen generation
Get PDFWe report the effect of incorporation of graphene nanoribbons (GNR) into a TiO2 mesoporous film sensitized with colloidal CdSe/CdS core/shell quantum dots (QDs) on the efficiency and long-term stability of a photoelectrochemical (PEC) cell for hydrogen (H2) generation. The GNR-TiO2 hybrid photoanodes were prepared by using simple, low-cost and large-area scalable doctor-blade method. The presence of GNR in the hybrid photoanode was confirmed by ultraviolet-visible absorption measurements, scanning electron microscopy and Raman spectroscopy. Our results demonstrate that an optimum loading of 0.02 wt% GNR increases the photocurrent density (at 0.8 V vs RHE) of the PEC device up to 5.51 mA/cm2, which is 30% higher than that of the control device. This improvement in photocurrent density can be attributed to enhanced electron transport (reduced charge transport resistance) in GNR-TiO2 hybrid anodes as confirmed by electrochemical impedance spectroscopy. In addition, PEC cells based on GNRs-TiO2/QDs hybrid photoanode maintain ∼65% of the initial photocurrent density after 7200 s of continuous one sun illumination, which is 15% higher than PEC cell based on a standard TiO2/QDs photoanode. Our findings offer a simple, large area scalable and low-cost approach to fabricate photoanode for high-performance optoelectronic devices, such as improving the performance of PEC cells for hydrogen generation
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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