Structure and Properties of High Stability Geminal Dicationic Ionic Liquids

Thirty-nine geminal dicationic ILs were synthesized and characterized in terms of their surface tensions, densities, melting points, refractive indices, viscosities, and miscibilities with a polar and nonpolar solvent. Two imidazolium or pyrrolidinium cations were joined via different length hydrocarbon linkage chains (from 3 to 12 carbons long). The various geminal dications were paired with up to four different anions. The effect of the dication type, linkage chain, alkyl substituents, and anion type on the physicochemical properties of these compounds was examined. Among the more interesting findings for this class of compounds was that their liquid and thermal stability ranges generally exceeded those of the more conventional, better known ILs. Indeed, this range was from −4 to \u3e400 °C for one of the pyrrolidinium-based geminal dicationic liquids. X-ray crystallography of the smaller solid ionic compounds indicated that there may be a correlation between the configurational degrees of freedom of the ILs and their melting points/glass transition temperatures. In one case, the crystal structure showed that a dicationic moiety had three distinct conformations in an asymmetric unit cell. The solvation properties of the geminal dicationic ILs tend to be similar to those of their monocationic analogues

A Convolutional Neural Network with Parallel Multi-Scale Spatial Pooling to Detect Temporal Changes in SAR Images

In synthetic aperture radar (SAR) image change detection, it is quite challenging to exploit the changing information from the noisy difference image subject to the speckle. In this paper, we propose a multi-scale spatial pooling (MSSP) network to exploit the changed information from the noisy difference image. Being different from the traditional convolutional network with only mono-scale pooling kernels, in the proposed method, multi-scale pooling kernels are equipped in a convolutional network to exploit the spatial context information on changed regions from the difference image. Furthermore, to verify the generalization of the proposed method, we apply our proposed method to the cross-dataset bitemporal SAR image change detection, where the MSSP network (MSSP-Net) is trained on a dataset and then applied to an unknown testing dataset. We compare the proposed method with other state-of-arts and the comparisons are performed on four challenging datasets of bitemporal SAR images. Experimental results demonstrate that our proposed method obtains comparable results with S-PCA-Net on YR-A and YR-B dataset and outperforms other state-of-art methods, especially on the Sendai-A and Sendai-B datasets with more complex scenes. More important, MSSP-Net is more efficient than S-PCA-Net and convolutional neural networks (CNN) with less executing time in both training and testing phases

Mesoporous CoS/ N‐doped Carbon as HER and ORR Bifunctional Electrocatalyst for Water Electrolysers and Zinc‐Air Batteries

Hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) are two critical electrocatalytic reactions, involved in many sustainable and green electrochemical energy conversion and storage technologies. Transition metal‐based compound combined with carbon materials have been found to be effective catalysts toward the HER and ORR with great potential to replace conventional precious metal‐based catalysts. Herein, a low‐cost method is described for the fabrication and testing of sulfide (CoS)/carbon compound with high specific surface area and mesoporous structure by using peptone as raw material and NaCl as template. The obtained materials showed open structures composed of interconnected thin carbon nanosheets with transition metal‐based nanoparticles wrapped inside the carbon matrix. These as‐prepared materials were used as HER and ORR bifunctional catalysts for water electrolysis and Zn‐air battery. In the alkaline media, the optimized catalysts exhibited highly efficient electrocatalysis toward the HER. They also showed an outstanding ORR activity and durability which was found to be superior to commercial Pt/C catalysts. In an assembled primary Zn‐air cell containing the optimized sample, the open circuit voltage (OCV) was 1.44 V, higher than the value for Zn‐air cell containing Pt/C. The assembled Zn‐air cell delivered a power density of 119 mW cm−2 at 150 mA cm−2, higher than the Pt/C cell (97 mW cm−2 at 150 mA cm−2)

Tailoring nanopores within nanoparticles of PtCo networks as catalysts for methanol oxidation reaction

It has been recently reported that engineering the pores within alloy nanoparticles leads to improvement in the electrochemical activity of nanoparticle catalysts due to the enhanced electrochemical active surface areas. However, to date, few works have reported the tailoring intraporosity within alloy nanoparticle networks. In this study, a different and innovative approach was adopted to yield a network-like PtCo catalyst composed of intraporous nanoparticles used a cotton-like PtCo precursor material. It was found that the network-like structure and intrapores within the nanoparticles could co-evolve after careful controlled electrochemical dealloying, whereby Pt-rich surface was formed during the leaching out of Co in the first 13th potentiostatic cyclic voltammetry cycles from +0.056 to +1.256 V vs. RHE. Electrochemical data also showed that the mass and area activity of the obtained PtCo networks toward methanol oxidation reaction (MOR) was nearly 3.9, 2.0 and 2.1 times higher than that of commercial Pt/C, PtRu/C catalyst respectively, and much higher than that of Pt3Co networks made of only solid nanoparticles. Moreover, it was observed that such networks exhibited high CO oxidation ability whilst maintaining high catalytic durability under an applied potential of +0.756 V vs. RHE. It was found that developing network-like catalysts composed of porous nanoparticles can be an efficient strategy to improve the catalytic activity and durability of fuel cell catalysts

Nano-engineering PdNi networks by voltammetric dealloying for ethanol oxidation

PdNi particle networks (PdNi NN) are prepared by voltammetric dealloying using catkin-like PdNi nanoparticles as precursor. It is found that voltammetric dealloying plays an important role for the formation of these networks. Electron microscopy and X-ray diffraction are employed to show the evolution of the morphology of the as-prepared catalysts. The results generated from the cyclic voltammetry experiments showed that the PdNi NN was electrocatalytically active toward the ethanol oxidation reaction (EOR). Compared with PdNi/C and commercial Pd/C, the oxidation peak potential of PdNi NN shifted positively by + 105 and + 168 mV, and the peak current density increased by 1.53 and 3.75 times. The high electrocatalytic activity of PdNi NN toward the EOR afforded the feasibility to exploit highly active electro catalysts for direct ethanol fuel cells

Structure and Properties of High Stability Geminal Dicationic Ionic Liquids

Thirty-nine geminal dicationic ILs were synthesized and characterized in terms of their surface tensions, densities, melting points, refractive indices, viscosities, and miscibilities with a polar and nonpolar solvent. Two imidazolium or pyrrolidinium cations were joined via different length hydrocarbon linkage chains (from 3 to 12 carbons long). The various geminal dications were paired with up to four different anions. The effect of the dication type, linkage chain, alkyl substituents, and anion type on the physicochemical properties of these compounds was examined. Among the more interesting findings for this class of compounds was that their liquid and thermal stability ranges generally exceeded those of the more conventional, better known ILs. Indeed, this range was from −4 to >400 °C for one of the pyrrolidinium-based geminal dicationic liquids. X-ray crystallography of the smaller solid ionic compounds indicated that there may be a correlation between the configurational degrees of freedom of the ILs and their melting points/glass transition temperatures. In one case, the crystal structure showed that a dicationic moiety had three distinct conformations in an asymmetric unit cell. The solvation properties of the geminal dicationic ILs tend to be similar to those of their monocationic analogues.Reprinted (adapted) with permission from Journal of the American Chemical Society 127 (2005): 593, doi: 10.1021/ja046521u. Copyright 2005 American Chemical Society.</p