Visualization of facet-dependent pseudo-photocatalytic behavior of TiO2 nanorods for water splitting using In situ liquid cell TEM

We report an investigation of the pseudo-photocatalytic behavior of rutile TiO2 nanorods for water splitting observed with liquid cell transmission electron microscopy (TEM). The electron beam serves as a “light” source to initiate the catalytic reaction and a “water-in-salt” aqueous solution is employed as the electrolyte. The observation reveals that bubbles are generated preferentially residing near the {110} facet of a rutile TiO2 nanorod under a low electron dose rate (9.3–18.6 e-/Å2·s). These bubbles are ascribed to hydrogen gas generated from the pseudo-photocatalytic water splitting. As the electron beam current density increases to 93 e-/Å2 ·s, bubbles are also found at the {001} and {111} facets as well as in the bulk liquid solution, demonstrating the dominant effects of water electrolysis by electron beam under higher dose rates. The facet-dependent pseudo-photocatalytic behavior of rutile TiO2 nanorods is further validated using density functional theory (DFT)calculation. Our work establishes a facile liquid cell TEM setup for the study of pseudo-photocatalytic water splitting and it may also be applied to investigation of other photo-activated phenomena occurring at the solid-liquid interfaces

Spatio-temporal changes of snowmelt in Greenland ice sheet based on SSM/I (SSMIS) data (1988-2016)

359-365The snowmelt of the Greenland ice sheets is of great significance to the study of global climate change. This paper is based on the 19.35 GHz horizontal polarization data and 37.00 GHz vertical polarization data of the Special Sensor Microwave/ Imager Sounder (SSMIS) and Special Sensor Microwave/ Image (SSM/I) carried by National Defense Meteorological Satellite Program (DMSP) from 1988 to 2016, by cross-polarization ratio (XPGR) algorithm (threshold value is -0.0158). The inter-annual trends of snowmelt area, annual average snowmelt onset, end date and duration in Greenland were studied. The results showed that the maximum snowmelt area was 2,080,000 km2 in 2012, and the minimum was 1,115,000 km2 in 1992. From 1988 to 2016, the snowmelt area of the Greenland ice sheets was increased by 2.8×105 km2, with a growth rate of 9.66×103 km2/year. In the annual average change rate, there were earlier snowmelt onset date (0.16 days earlier each year), longer snowmelt duration (0.36 days longer each year) and later snowmelt end date (0.06 days later each year), and the snowmelt area was in the marginal region. The snowmelt area of the southern margin is the largest, and there are obvious regional differences. The snowmelt of Greenland ice sheets changes greatly and shows a periodic change rule in the annual mean snowmelt variation

Time-Dependent Partition-Free Approach in Resonant Tunneling Systems

An extended Keldysh formalism, well suited to properly take into account the initial correlations, is used in order to deal with the time-dependent current response of a resonant tunneling system. We use a \textit{partition-free} approach by Cini in which the whole system is in equilibrium before an external bias is switched on. No fictitious partitions are used. Besides the steady-state responses one can also calculate physical dynamical responses. In the noninteracting case we clarify under what circumstances a steady-state current develops and compare our result with the one obtained in the partitioned scheme. We prove a Theorem of asymptotic Equivalence between the two schemes for arbitrary time-dependent disturbances. We also show that the steady-state current is independent of the history of the external perturbation (Memory Loss Theorem). In the so called wide-band limit an analytic result for the time-dependent current is obtained. In the interacting case we propose an exact non-equilibrium Green function approach based on Time Dependent Density Functional Theory. The equations are no more difficult than an ordinary Mean Field treatment. We show how the scattering-state scheme by Lang follows from our formulation. An exact formula for the steady-state current of an arbitrary interacting resonant tunneling system is obtained. As an example the time-dependent current response is calculated in the Random Phase Approximation.Comment: final version, 18 pages, 9 figure