72 research outputs found
Self-optimizing, highly surface-active layered metal dichalcogenide catalysts for hydrogen evolution
Low-cost, layered transition-metal dichalcogenides (MX_2) based on molybdenum and tungsten have attracted substantial interest as alternative catalysts for the hydrogen evolution reaction (HER). These materials have high intrinsic per-site HER activity; however, a significant challenge is the limited density of active sites, which are concentrated at the layer edges. Here we unravel electronic factors underlying catalytic activity on MX_2 surfaces, and leverage the understanding to report group-5 MX_2 (H-TaS_2 and H-NbS_2) electrocatalysts whose performance instead mainly derives from highly active basal-plane sites, as suggested by our first-principles calculations and performance comparisons with edge-active counterparts. Beyond high catalytic activity, they are found to exhibit an unusual ability to optimize their morphology for enhanced charge transfer and accessibility of active sites as the HER proceeds, offering a practical advantage for scalable processing. The catalysts reach 10 mA cm^(−2) current density at an overpotential of ∼50–60 mV with a loading of 10–55 μg cm^(−2), surpassing other reported MX2 candidates without any performance-enhancing additives
Electro-oxidation of cyanide on active and non-active anodes: Designing the electrocatalytic response of cobalt spinels
[EN] The feasibility of the electrochemical technologies for wastewater treatment greatly relies on the design of
efficient but inexpensive electrocatalysts. It is generally accepted that the so-called ¿non-active¿ anodes (like the
boron-doped diamond (BDD) or SnO2-based anodes), producing highly oxidizing hydroxyl radicals, are the most
promising candidates for pollutants abatement. In this work, the electrocatalytic performance of various cobalt
oxides, pure and doped with Cu or Au, for CN¿ oxidation has been studied and compared with that of conventional
graphite, BDD, SnO2-Sb and SnO2-Sb-Pt. The metal oxide electrodes were prepared by thermal decomposition
of the salt precursors onto Ti. For the M-doped Co3O4 electrodes, the nominal M/Co ratios were Cu/
Co=0.07¿1.00; and Au/Co=0.05¿0.20. The electrodes were characterized by different techniques (XRD, SEM,
EDX, XPS) and their electrocatalytic response was studied by cyclic voltammetry and galvanostatic electrolysis in
a H-type cell in aqueous 0.1M NaOH. The obtained results show that the nature of the dopant plays a key role on
the electrocatalytic behavior of cobalt spinels. Thus, while Cu catalyzes the CN¿ electro-oxidation, Au declines
it. This is explained by the fact that, unlike Au (which segregates as Au-rich particles), Cu is effectively incorporated
into the spinel structure by forming a solid solution (CuxCo3-xO4). In this solid solution, atomic scale
Cu(spinel)-CN¿ specific interactions occur to catalyze the reaction, whereas in segregated Au particles the oxidation
is hindered probably by a too-strong adsorption of cyanide and/or its inaccessibility to oxide active sites.
Electrolysis runs have revealed that ¿active¿ over-saturated Cu-doped spinels (Cu/Co=1.00) exhibit higher
current efficiencies than conventional graphite and ¿non-active¿ BDD and SnO2-based anodes. Hence, we hereby
demonstrate that an inexpensive ¿active¿ electrocatalyst can show even higher efficiency than the most powerful
BDD anode. These results highlight the significance of anode design in the application of the electrochemical
technique for wastewater treatment.Financial support from the Spanish Ministerio de Economia y Competitividad and FEDER funds (MAT2016-76595-R, IJCI-2014-20012) is gratefully acknowledgedBerenguer, R.; Quijada, C.; La Rosa-Toro, A.; Morallón, E. (2019). Electro-oxidation of cyanide on active and non-active anodes: Designing the electrocatalytic response of cobalt spinels. Separation and Purification Technology. 208:42-50. https://doi.org/10.1016/j.seppur.2018.05.024S425020
Juegos interactivos para el desarrollo de la autonomía en los niños de primer grado de preescolar
Licenciatura en Educació
Effect of topdressing on individual leaf photosynthesis at different position in direct-sown rice with non-woven fabric mulch system
Direct sowing with non-woven fabric mulch is the new organic rice cultivation system. We studied the effect of topdressing on individual leaf photosynthesis at different position and grain yield in rice plants cultivated by this system. Leaf photosynthetic rate at the different leaf position per plant (P N-LP) of the third and fourth to lower leaves was higher when the topdressing amount was increased. Without topdressing or in no-fertilizers plots, the P N-LP values of lower leaves were very low. The leaf photosynthetic rate per unit leaf area (P N-LA) decreased gradually as the leaf position became lower. Again, the P N-LA values of the top-dressed plots at the lower leaves were higher than that of plots without topdressing or without fertilizers. The lower leaves maintained a higher P N because of a higher rate of nitrogen accumulation due to topdressing. The higher rate of photosynthesis in these leaves resulted in better root activity, which contributed to a better ripening percentage and ultimately higher rice grain yield
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