Effects of Reduction Methods on the Performance of Shewanella oneidensis MR-1 Palladium/Carbon Catalyst for Oxygen Reduction Reaction.

The influence of the reduction method on the morphology and performance of the catalyst still controversial. In this study, hydrogen, Shewanella oneidensis MR-1 (MR-1), MR-1 and hydrogen coreduction are used to reduce the palladium ions adsorbed by MR-1 to obtain Pd/CH2, Pd/CM, and Pd/CH2+M catalyst, respectively. It is found that the palladium nanoparticles (Pd NPs) in Pd/CH2+M are the largest, while the Pd NPs in Pd/CM are the smallest. This is due to the reduction of Pd NPs in Pd/CH2+M under anaerobic conditions to form smaller Pd NPs that will further aggregate and grow in H2. In addition, Pd/CM exhibited the best catalytic performance with a mass activity of 0.31 A mg-1, better than that of Pd/CH2 (0.06 A mg-1) and Pd/CH2+M (0.13 A mg-1). This study provides a meaningful reference for the selection of reduction methods in metal catalysts.

Preparation and Performance of a Cu@PtCu/CNF Oxygen Reduction Catalyst Membrane by Electrospinning.

A flexible carbon nanofiber film with high conductivity was prepared by electrospinning, and then Cu was uniformly deposited on the fiber film by pulse electrodeposition to prepare Cu nanocrystal/carbon nanofiber film. Cu@PtCu/carbon nanofiber (Cu@PtCu/CNF) catalytic films were synthesized by in-situ substitution reduction. The Cu@PtCu/CNF catalytic film solves the problem of uneven activity of the catalytic layer and can be directly used as the catalytic layer. The morphology and structure were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Electrochemical test results show that the Cu@PtCu/CNF catalytic films obtained at the chloroplatinic acid concentration of 0.5 mg·mL-1 (N2) exhibited 2.5 times specific activity when compared with commercial Pt/C catalysts. After 5000 cycles of stability test, the electrochemical surface areas (ECSAs) were still maintained at 80%, and the half-wave potential decreased by 11 mV, which was better than those of commercial Pt/C catalysts.

Preparation of Low Grain Boundary Perovskite Crystals with Excellent Performance: The Inhibition of Ammonium Iodide.

For the study, we prepared a low grain boundary three-dimensional CH3NH3PbI3 crystal (3D-MAPbI3) on TiO2 nanoarrays by inhibition of ammonium iodide and discussed the formation mechanism of the crystal. Based on the 3D-MAPbI3 crystal, solar cells showed modified performance with a power conversion efficiency (PCE) of up to 19.3%, which increases by 36.8% in contrast to the counterparts. We studied the internal photocurrent conversion process. The highest external quantum efficiency is up to 92%, and the electron injection efficiency is remarkably facilitated where the injection time decreases by 37.8% compared to the control group. In addition, based on 3D-MAPbI3, solar cells showed excellent air stability, which possesses 78.3% of the initial PCE, even though they were exposed to air for 30 days. Our results demonstrate a promising approach for the fabrication of perovskite solar cells with high efficiency and stability.

Evaporation-induced self-assembly of quantum dots-based concentric rings on polymer-based nanocomposite films.

The "ball-on-film" template is used to construct concentric rings on the surface of PMMA-QDs (polymethyl methacrylate - quantum dots) nanocomposite films via the evaporation of pure chloroform droplets, which are confined by a steel ball. The concentric rings consist of QDs, as revealed by the fluorescence images of the concentric rings. The photoluminescence intensity of the concentric rings increases with the increase of the distance to the ball center, suggesting that the amount of QDs accumulated around the contact line at individual stick state increases with the increase of the distance to the ball center. Both the wavelength and cross-sectional area (width) of the concentric rings increase approximately linearly with increasing distance to the ball center, independent of the ball size, the film thickness and the QDs concentration. For the PMMA-QDs nanocomposite films prepared from the same QDs concentration in chloroform, the thicker the PMMA-QDs nanocomposite film, the larger the wavelength for the same distance to the ball center. The effect of confinement of two steel balls on the surface patterns over the PMMA-QDs nanocomposite films is studied via a template of "two spheres on film". Symmetric surface patterns are formed. There exist two types of featureless zone between the two balls, depending on the distance between the two balls: one is the inner featureless zone and the other is the outer featureless zone. The size of both featureless zones increases with the increase of the ball distance.

Metal crack propagation monitoring by photoluminescence enhancement of quantum dots.

A visualization method for monitoring minor metal crack propagation is presented in this paper. Through CdS@ZnS core-shell quantum dots (QDs) enhanced emission of photoluminescence (PL), this crack detection method provides a visualization signal in real time and through a noncontact fashion. The crack of the CdS@ZnS core-shell QDs-epoxy resin kept a synchronous propagation with the metal crack. Detection of the tip growth in the film layers demonstrated that the actual crack propagation on the metal surface could be deduced from the tips in the film layers. The fluorescence peak tended to increase along the crack from the initial opening to the tip. Crack width as small as 10 µm can be detected with a precision of 0.1 µm and the minimum crack tip width of the QDs-epoxy resin was measured as 0.72 µm.