RESUMEN

In this paper, a novel, simple and mild soft template assisted strategy and further carbonization approach has been constructed to the size-tunable preparation of porous Cu-N-C/Surfactant catalysts successfully. Note that the pluronic F127 has a significant influence on the synthesis of porous Cu-N-C/F127 with the atomically dispersed Cu-N4 and adjacent Cu atomic clusters (ACs) than other surfactants owing to their particular non-ionic structure. By combining a series of experimental analysis and density functional theory (DFT) calculations, the synergistic effects between the adjacent Cu ACs and atomically dispersed Cu-N4 are favorable for manipulating the binding energy of O2 adsorption and intermediates desorption at the atomic interface of catalysts, resulting in an excellent electrocatalytic ORR performance with a faster kinetics for Cu-N-C/F127 than those of the Cu-N-C, Cu-N-C/CTAB, Cu-N-C/SDS, and comparable with the commercial Pt/C catalyst. This method not only provides a novel approach for synthesizing highly effective copper based single atom catalysts toward ORR, but also offers an in-depth understanding of the synergisms of adjacent ACs on the Cu single atoms (SAs) for highly effective electrocatalytic ORR and Zn-air Battery.

RESUMEN

Herein, a soft-template strategy involving the cationic surfactants has been successfully applied to size-controlled synthesis of hierarchical porous Fe-N/C for the first time. Specifically, a small amount of Fe and cationic surfactants can be uniformly doped into the zinc-based zeolite imidazole framework (ZIF-8) crystal particles and the cationic surfactants play a critical role in the formation of hierarchically porous Fe-ZIF-8@surfactant precursors. When the Fe-ZIF-8@surfactant is subsequently pyrolyzed, atomically dispersed Fe-Nx coordination structures can be in-situ converted to Fe-N/C, while the cationic surfactants decompose to form a carbon matrix to encapsulate the active sites, thereby preventing the aggregation of nanoparticles to a certain extent. As a result, the combined Fe nanocrystals and atomically dispersed Fe-Nx in the graphitic carbon matrix generate a synergistic effect to boost the electrocatalytic behaviors with a more positive half-wave potential (0.92 V) for oxygen reduction reaction (ORR) and a lower overpotential (420 mV at 10 mA cm-2) for oxygen evolution reaction (OER). As a proof of concept, the Fe-N/C@TTAB based zinc-air batteries (ZABs) present an outstanding peak power density (107.9 mW cm-2) and a superior specific capacity (706.3 mAh g-1) with robust cycling stability over 900 cycles for 150 h, which are better than the commercial Pt/C + IrO2 based ZABs.

RESUMEN

The microstructure and performance of magnesium potassium phosphate cement (MKPC), a kind of magnesium phosphate cement (MPC), are determined by the hydration products. In this paper, the hydration behavior of MKPC is investigated through various material characterization methods and thermodynamic modeling, including X-ray diffraction (XRD), thermogravimetric and differential scanning calorimeter (TG/DSC), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and GEMS software. The results of XRD, TG/DSC and SEM all indicate that K-struvite (MgKPO4·6H2O) is the main hydration product of MKPC. When the curing age is 1 day and 28 days, the TG data indicate that the mass loss of MKPC in the range of 60-200 °C is 17.76% and 17.82%, respectively. The MIP results show that the porosity of MKPC is 29.63% and 29.61% at the curing age of 1 day and 28 days, respectively, which indicates that the structure of MKPC becomes denser with the increase in curing age. In addition, the cumulative pore volume of MKPC at the curing age of 28 days is 2.8% lower than that at 1 day, and the pore diameters are shifted toward the small pores. Furthermore, the thermodynamic modeling is well suited to make an analysis of the hydration behavior of MKPC.

RESUMEN

Attention, referring to selective processing of task-related information, is central to cognition. It has been proposed that voluntary attention (driven by current goals or tasks and under top-down control) and reflexive attention (driven by stimulus salience and under bottom-up control) struggle to control the focus of attention with interaction in a push-pull fashion for everyday perception in higher vertebrates. However, how auditory attention engages in auditory perception in lower vertebrates remains unclear. In this study, each component of auditory event-related potentials (ERP) related to attention was measured for the telencephalon, diencephalon and mesencephalon in the Emei music frog (Nidirana daunchina), during the broadcasting of acoustic stimuli invoking voluntary attention (using binary playback paradigm with silence replacement) and reflexive attention (using equiprobably random playback paradigm), respectively. Results showed that (1) when the sequence of acoustic stimuli could be predicted, the amplitudes of stimulus preceding negativity (SPN) evoked by silence replacement in the forebrain were significantly greater than that in the mesencephalon, suggesting voluntary attention may engage in auditory perception in this species because of the correlation between the SPN component and top-down control such as expectation and/or prediction; (2) alternately, when the sequence of acoustic stimuli could not be predicted, the N1 amplitudes evoked in the mesencephalon were significantly greater than those in other brain areas, implying that reflexive attention may be involved in auditory signal processing because the N1 components relate to selective attention; and (3) both SPN and N1 components could be evoked by the predicted stimuli, suggesting auditory perception of the music frogs might invoke the two kind of attention resources simultaneously. The present results show that human-like ERP components related to voluntary attention and reflexive attention exist in the lower vertebrates also.

RESUMEN

Thermodynamically induced tensile stress in the perovskite film will lead to the formation of atomic vacancies, seriously destroying the photovoltaic efficiency stability of the perovskite solar cells (PSCs). Among them, cations and halide anions vacancies are unavoidable; these point vacancies are considered to be a major source of the ionic migration and perovskite degradation at the crystal boundary and surface of the perovskite films. Here, we use choline bromide to modify the perovskite film by occupying the atomic defects in the CsPbBr3 perovskite film. The results show that the zwitterion quaternary ammonium ions and bromide ions in choline bromide can simultaneously occupy the Cs+ cation and Br- anions vacancies in the perovskite film by the ionic bonding effect, for which the defect-state density on the surface of the perovskite film can be significantly reduced, leading to the effective enhancement of carrier lifetime. In addition, the residual stress at the crystal boundary can be effectively reduced by lowering the Young's modulus in the CsPbBr3 perovskite film. As a result, the optimized device achieves a photoelectric conversion efficiency (PCE) of 9.06% with an increase of 41.1% compared to the control device with a PCE of 6.42%. Most importantly, the newborn thermal stress due to thermal expansion during heat working conditions can be transferred from the polycrystalline perovskite to the carbon layer by the matched Young's modulus, thus resulting in improved stability perovskite film under environmental conditions. The work provides new insights for preparing high-quality perovskite films with low defect-state density and residual stress.

RESUMEN

In this study, we, for the first time, demonstrate a general solid-phase pyrolysis method to synthesize hybrid transition metal nanocrystal-embedded graphitic carbon nitride nanosheets, namely M-CNNs, as a highly efficient oxygen electrocatalyst for rechargeable Zn-air batteries (ZABs). The ratios between metallic acetylacetonates and the g-C3N4 precursor can be controlled where Fe-CNNs-0.7, Ni-CNNs-0.7 and Co-NNs-0.7 composites have been optimized to exhibit superior ORR/OER bifunctional electrocatalytic activities. Specifically, Co-CNNs-0.7 exhibited not only a comparable half-wave potential (0.803 V vs. RHE) to that of the commercial Pt/C catalyst (0.832 V) with a larger current density for the ORR but also a lower overpotential (440 mV) toward the OER compared with the commercial IrO2 catalyst (460 mV), revealing impressive application in rechargeable ZABs. As a result, ZABs using Co-CNNs-0.7 as the cathode exhibited an excellent peak power density of 85.3 mW cm-2 with a specific capacity of 675.7 mA h g-1 and remarkable cycling stability of 1000 cycles, outperforming the commercially available Pt/C + IrO2 catalysts. This study highlights the synergy from heterointerfaces in oxygen electrocatalysis, thus providing a promising approach for advanced metal-air cathode materials.

RESUMEN

The high cost and platinum dissolution issues of counter electrodes (CEs) are two core problems for the development of dye-sensitized solar cells (DSSCs). In this work, different CEs based on binary alloy Ru81.09Co18.91, Ru80.55Se19.45 and Co20.85Se79.15 nanostructures for DSSCs were successfully synthesized and investigated by a facile and environmentally friendly approach. Here, we found that the Co20.85Se79.15 alloy CE-based device yields the higher photoelectric conversion efficiency of 7.08% compared with that (5.80%) of the DSSC using a pure Pt CE because of the larger number of active sites with improved charge transferability and reduced interface resistance by matching work function with the I3‒/I‒ redox electrolyte. The inexpensive synthesis method, cost-effectiveness and superior catalytic activity of the Co20.85Se79.15 alloy may open up a new avenue for the development of CEs for DSSCs in the near future.

RESUMEN

We demonstrate, for the first time, a new method of fabricating hybrid MoS2/poly(ethyleneimine)-modified graphene oxide (PEI-GO) composites assembled through electrostatically charged interaction between the negatively charged MoS2 nanosheets and positively charged PEI-GO in an aqueous solution. The GO can not only improve the electronic conductivity of the MoS2/PEI-GO composites, leading to an excellent charge-transfer network, but also hamper the restacking of MoS2 nanosheets. The composition ratios between MoS2 and PEI-GO were also optimized with the highest specific capacitance of 153.9 F g-1 where 96.0% of the initial specific capacitance remains after 6800 cycles. The specific capacitance of only 117.5 F g-1 was observed for the pure MoS2 nanosheets, and 68.2% of the initial specific capacitance was achieved after 5000 cycles. The excellent electrochemical performance of the hybrid MoS2/PEI-GO composites was demonstrated by establishing an asymmetric supercapacitor with a MoS2/PEI-GO-based negative electrode and an activated-carbon positive electrode. The asymmetric supercapacitor provided a maximum capacitance of 42.9 F g-1, and 93.1% of the initial capacitance was maintained after 8000 cycles. Furthermore, a MoS2/PEI-GO//activated-carbon asymmetric supercapacitor delivered an energy density of 19.3 W h kg-1 and a power density of 4500 W kg-1, indicating the potential of the hybrid MoS2/PEI-GO composites in electrochemical energy storage applications.

RESUMEN

Here we report a novel solid-state ECL sensor for ultrasensitive sensing of glutathione (GSH) based on ferrocyanide-ferricyanide redox couple (Fe(CN)6(3-/4-)) induced electrochemiluminescence (ECL) amplification of carbon dots (C-dots). The electropolymerization of C-dots and (11-pyrrolyl-1-yl-undecyl) triethylammonium tetrafluoroborate (A2) enabled immobilization of the hydrophilic C-dots on the surface of glassy carbon electrode (GCE) perfectly, while the excellent conductivity of polypyrrole was exploited to accelerate electron transfer between them. The Fe(CN)6(3-/4-) can expeditiously convert the C-dots and S2O8(2-) to C-dot(•-) and SO4(•-), respectively. High yields of the excited state C-dots (C-dots*) were obtained, and a ∼10-fold ECL amplification was realized. The C-dots* obtained through the recombination of electron-injected and hole-injected processes may be impeded due to the interference of GSH to K2S2O8. Therefore, the constructed sensor for GSH showed a detection limit down to 54.3 nM (S/N = 3) and a wide linear range from 0.1-1.0 µM with a correlation coefficient of 0.997.

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