No abstract

Single noble metal atoms and ultrafine metal clusters catalysts tend to sinter into aggregated particles at elevated temperatures, driven by the decrease of metal surface free energy. Herein, we report an unexpected phenomenon that noble metal nanoparticles (Pd, Pt, Au-NPs) can be transformed to thermally stable single atoms (Pd, Pt, Au-SAs) above 900 °C in an inert atmosphere. The atomic dispersion of metal single atoms was confirmed by aberration-corrected scanning transmission electron microscopy and X-ray absorption fine structures. The dynamic process was recorded by in situ environmental transmission electron microscopy, which showed competing sintering and atomization processes during NP-to-SA conversion. Further, density functional theory calculations revealed that high-temperature NP-to-SA conversion was driven by the formation of the more thermodynamically stable Pd-N structure when mobile Pd atoms were captured on the defects of nitrogen-doped carbon. The thermally stable single atoms (Pd-SAs) exhibited even better activity and selectivity than nanoparticles (Pd-NPs) for semi-hydrogenation of acetylene.

No abstract

Small molecules, namely, DCAO(3)TBDT and DR(3)TBDT, with 2-ethylhexoxy substituted BDT as the central building block and octyl cyanoacetate and 3-ethylrhodanine as different terminal units with the same linkage of dioctyltertthiophene, have been designed and synthesized. The photovoltaic properties of these two molecules as donors and fullerene derivatives as the acceptors in bulk heterojunction solar cells are studied. Among them, DR(3)TBDT shows excellent photovoltaic performance, and power conversion efficiency as high as 7.38% (certified 7.10%) under AM 1.5G irradiation (100 mW cm(-2)) has been achieved using the simple solution spin-coating fabrication process, which is the highest efficiency reported to date for any small-molecule-based solar cells. The results demonstrate that structure fine turning could cause significant performance difference and with that the performance of solution-processed small-molecule solar cells can indeed be comparable with or even surpass their polymer counterparts.

No abstract

Novartis Pharma AG.

In the past few years, great progress has been made in organic photovoltaic (OPV) cells for an alternate of silicon semiconductorbased solar cells. OPV has the advantages of clean, low-cost, flexibility, and the possibility of roll-to-roll production. [1][2][3][4] Currently, most of the works have been focused on polymer donor molecules using bulk heterojunction (BHJ) architecture and [6,6]-phenyl-C61-butyric acid methyl ester (PC 61 BM) as the acceptor. [5,6] Indeed, in addition to the currently better OPV performance than small molecules, polymers have the advantages for such as better film forming quality and so on. [7] However, it cannot be denied that there are disadvantages for polymer-based OPV, such as batch to batch reproducibility, difficulty of purification, and so on. In contrast, small molecules intrinsically do not have such flaws; [8] additionally, their band structures could be tuned easily with much more choices of chemical modification. Furthermore, small molecules generally have higher charge mobility and open voltages. [9,10] However, even with these advantages, small-molecule-based OPV cells have not been investigated as intensively as that of their polymer counterparts because one of the major problems for small molecules is their generally poor film quality when using the simple solution spinning process. [11] This has been hampering their performance, and indeed their power conversion efficiencies (PCEs) (4%-5%) [12][13][14][15][16][17][18] are still significantly lower compared with that (>7%) [19][20][21][22][23][24][25] from polymers. It is thus expected that better PCE could be achieved when their intrinsic bad film quality and morphology in BHJ architecture could be improved combining with their other advantages. But to achieve this, careful molecule design has to be carried out to address many factors collectively, including their molar absorption, morphology compatibility with the acceptors for a better film quality, and so on.Previously, we have reported a small molecule (DCAO7T, Scheme 1), which gives rather high quality of solution spincoated film and a high 5.08% PCE. [12] But this molecule comes with an end unit of cyanoacetate group, which could not contribute too much for the overall solar absorption. So, we thought that the current density J sc might be able to be enhanced if structures with stronger molar absorption is used to replace such an end unit, in the conditions that overall molecular backbone and morphology will not be affected too much. Considering the generally high absorption coefficients and good OPV performance of many dye molecules, such as triarylamines, [16,26] acenaphthoquinoxaline, [27] diketopyrrolopyrroles (DPP), [17] squaraines, [18,28,29] merocyanine, [30,31] isoindigo, [32] pthalocyanine, [33] and dipyrromethene boron difluoride (BODIPY), [34][35][36] we thus introduce a new dye unit, 3-ethylrhodanine, into the targeted OPV molecule named as DERHD7T (Scheme 1) with a conjugated thiophene backbone. With such a design, DERHD7T is expected to have a str...

The Tienshan Mountains, with its status as “water tower”, is the main water source and ecological barrier in Central Asia. The rapid warming affected precipitation amounts and fraction as well as the original glacier/snowmelt water processes, thereby affecting the runoff and water storage. The ratio of snowfall to precipitation (S/P) experienced a downward trend, along with a shift from snow to rain. Spatially, the snow cover area in Middle Tienshan Mountains decreased significantly, while that in West Tienshan Mountains increased slightly. Approximately 97.52% of glaciers in the Tienshan Mountains showed a retreating trend, which was especially obvious in the North and East Tienshan Mountains. River runoff responds in a complex way to changes in climate and cryosphere. It appears that catchments with a higher fraction of glacierized area showed mainly increasing runoff trends, while river basins with less or no glacierization exhibited large variations in the observed runoff changes. The total water storage in the Tienshan Mountains also experienced a significant decreasing trend in Middle and East Tienshan Mountains, but a slight decreasing trend in West Tienshan Mountains, totally at an average rate of −3.72 mm/a. In future, water storage levels are expected to show deficits for the next half-century.