Crystalline–amorphous phase boundary engineering can be an effective strategy to develop cost-effective and high-performance electrocatalysts for water splitting.

We demonstrate the improved efficiency of a Cu2Zn(Sn1− x Ge x )Se4 (CZTGSe) thin-film solar cell with a conversion efficiency of 12.3%; this cell exhibits a greatly improved open-circuit voltage (V OC) deficit of 0.583 V and a fill factor (FF) of 0.73 compared with previously reported CZTGSe cells. The V OC deficit was found to be improved through a reduced band tailing via the control of the Ge/(Sn + Se) ratio. In addition, the high FF was mainly induced by a reduced carrier recombination at the absorber/buffer interface and/or in the space charge region, whereas parasitic resistive effects on FF were very small.

Yarn-based supercapacitors having improved performance are needed for existing and emerging wearable applications. Here, we report weavable carbon nanotube yarn supercapacitors having high performance because of high loadings of rapidly accessible charge storage particles (above 90 wt% MnO2). The yarn electrodes are made by a biscrolling process that traps host MnO2 nanoparticles within the galleries of helically scrolled carbon nanotube sheets, which provide strength and electrical conductivity. Despite the high loading of brittle metal oxide particles, the biscrolled solid-state yarn supercapacitors are flexible and can be made elastically stretchable (up to 30% strain) by over-twisting to produce yarn coiling. The maximum areal capacitance of the yarn electrodes were up to 100 times higher than for previously reported fibres or yarn supercapacitors. Similarly, the energy density of complete, solid-state supercapacitors made from biscrolled yarn electrodes with gel electrolyte coating were significantly higher than for previously reported fibre or yarn supercapacitors.

To maximize the number of planet detections, current microlensing follow-up observations are focusing on high-magnification events which have a higher chance of being perturbed by central caustics. In this paper, we investigate the properties of central caustics and the perturbations induced by them. We derive analytic expressions of the location, size, and shape of the central caustic as a function of the star-planet separation, $s$, and the planet/star mass ratio, $q$, under the planetary perturbative approximation and compare the results with those based on numerical computations. While it has been known that the size of the planetary caustic is \propto \sqrt{q}, we find from this work that the dependence of the size of the central caustic on $q$ is linear, i.e., \propto q, implying that the central caustic shrinks much more rapidly with the decrease of $q$ compared to the planetary caustic. The central-caustic size depends also on the star-planet separation. If the size of the caustic is defined as the separation between the two cusps on the star-planet axis (horizontal width), we find that the dependence of the central-caustic size on the separation is \propto (s+1/s). While the size of the central caustic depends both on $s$ and q, its shape defined as the vertical/horizontal width ratio, R_c, is solely dependent on the planetary separation and we derive an analytic relation between R_c and s. Due to the smaller size of the central caustic combined with much more rapid decrease of its size with the decrease of q, the effect of finite source size on the perturbation induced by the central caustic is much more severe than the effect on the perturbation induced by the planetary caustic. Abridged.Comment: 5 pages, 4 figures, ApJ accepte

The electrocatalytic performance of transition metal sulfide (TMS)− graphene composites has been simply regarded as the results of high conductivity and the large surface/volume ratio. However, unavoidable factors such as degree of oxidation of TMSs have been hardly considered for the origin of this catalytic activity of TMS−graphene composites. To accomplish the reliable application of TMS-based electrocatalytic materials, a clear understanding of the thermodynamic stability of TMS and effects of oxidation on catalytic activity is necessary. In addition, the mechanism of charge transfer at the TMS−graphene interface must be studied in depth to properly design composite materials. Herein, we report a comprehensive study of the physical chemistry at the junction of a Co 1−x Ni x S 2 −graphene composite, which is a prototype designed to unravel the mechanisms of charge transfer between TMS and graphene. Specifically, the thermodynamic stability and the effects of oxidation of TMSs during the oxygen evolution reaction (OER) on the reaction mechanism are systematically investigated using density functional theory (DFT) calculations and experimental observations. Cobalt atoms anchored on pyridinic N sites in the graphene support form metal−semiconductor (SC) junctions, and the internal band bending at these junctions facilitates electron transfer from TMSs to graphene. The junction enables fast sinking of the excess electron from OH − adsorbate. Partially oxidized amorphous TMS layers formed during the OER can facilitate adsorption and desorption of OH and H atoms, boosting the OER performance of TMS−graphene nanocomposites. From the DFT calculations, the enhanced electrocatalytic activity of TMS−graphene nanocomposites originates from two important factors: (i) increased internal band bending and (ii) parallelized OER pathways at the interface of pristine and oxidized TMSs.