Nickel diselenide (NiSe(2)) has been synthesized and applied as a counter electrode (CE) of dye-sensitized solar cells (DSSCs) for the first time, which displays remarkable catalytic activity in the reduction of I(3)(-). The DSSC with a NiSe(2) CE produces a higher power conversion efficiency (8.69%) than that (8.04%) of the cell with a Pt CE under the same conditions. A new method for comparing the catalytic activity has also been proposed.

NiS2 nanoparticles and nanocomposites of NiS2 with reduced graphene oxide (NiS2@RGO) have been successfully prepared via a facile hydrothermal reaction of nickel ions and sulfur source in the absence or presence of graphene oxide. NiS2@RGO nanocomposites exhibit excellent electrocatalytic performance for reduction of triiodide, owing to the improved conductivity and positive synergetic effect between NiS2 and RGO. As a consequence, the dye-sensitized solar cell with the NiS2@RGO counter electrode (CE) produces a power conversion efficiency of 8.55%, which is higher than that (7.02%) for the DSSC with the NiS2 CE, higher than that (3.14%) for the DSSC with the RGO CE, and also higher than that (8.15%) for the DSSC with the reference Pt CE under the same conditions.

In December 2019, the novel coronavirus pneumonia (COVID-19) occurred in Wuhan, Hubei Province, China. The epidemic quickly broke out and spread throughout the country. Now it becomes a pandemic that affects the whole world. In this study, three models were used to fit and predict the epidemic situation in China: a modified SEIRD (Susceptible-Exposed-Infected-Recovered-Dead) dynamic model, a neural network method LSTM (Long Short-Term Memory), and a GWR (Geographically Weighted Regression) model reflecting spatial heterogeneity. Overall, all the three models performed well with great accuracy. The dynamic SEIRD prediction APE (absolute percent error) of China had been � 1.0% since Mid-February. The LSTM model showed comparable accuracy. The GWR model took into account the influence of geographical differences, with R 2 = 99.98% in fitting and 97.95% in prediction. Wilcoxon test showed that none of the three models outperformed the other two at the significance level of 0.05. The parametric analysis of the infectious rate and recovery rate demonstrated that China's national policies had effectively slowed down the spread of the epidemic. Furthermore, the models in this study provided a wide range of implications for other countries to predict the short-term and long-term trend of COVID-19, and to evaluate the intensity and effect of their interventions.

As a model system for understanding charge transfer in novel architectural designs for solar cells, double-walled carbon nanotube (DWNT)–CdSe quantum dot (QD) (QDs with average diameters of 2.3, 3.0, and 4.1 nm) heterostructures have been fabricated. The individual nanoscale building blocks were successfully attached and combined using a hole-trapping thiol linker molecule, i.e., 4-mercaptophenol (MTH), through a facile, noncovalent π–π stacking attachment strategy. Transmission electron microscopy confirmed the attachment of QDs onto the external surfaces of the DWNTs. We herein demonstrate a meaningful and unique combination of near-edge X-ray absorption fine structure (NEXAFS) and Raman spectroscopies bolstered by complementary electrical transport measurements in order to elucidate the synergistic interactions between CdSe QDs and DWNTs, which are facilitated by the bridging MTH molecules that can scavenge photoinduced holes and potentially mediate electron redistribution between the conduction bands in CdSe QDs and the C 2p-derived states of the DWNTs. Specifically, we correlated evidence of charge transfer as manifested by (i) changes in the NEXAFS intensities of π* resonance in the C K-edge and Cd M 3-edge spectra, (ii) a perceptible outer tube G-band downshift in frequency in Raman spectra, as well as (iii) alterations in the threshold characteristics present in transport data as a function of CdSe QD deposition onto the DWNT surface. In particular, the separate effects of (i) varying QD sizes and (ii) QD coverage densities on the electron transfer were independently studied.