In Situ Photodeposition of Cobalt Phosphate (CoHxPOy) on CdIn2S4 Photocatalyst for Accelerated Hole Extraction and Improved Hydrogen Evolution.

The ternary metal sulfide CdIn2S4 (CIS) has great application potential in solar-to-hydrogen conversion due to its suitable band gap, good stability and low cost. However, the photocatalytic hydrogen (H2) evolution performance of CIS is severely limited by the rapid electron-hole recombination originating from the slow photogenerated hole transfer kinetics. Herein, by simply depositing cobalt phosphate (CoHxPOy, noted as Co-Pi), a non-precious co-catalyst, an efficient pathway for accelerating the hole transfer process and subsequently promoting the H2 evolution reaction (HER) activity of CIS nanosheets is developed. X-ray photoelectron spectroscopy (XPS) reveals that the Co atoms of Co-Pi preferentially combine with the unsaturated S atoms of CIS to form Co-S bonds, which act as channels for fast hole extraction from CIS to Co-Pi. Electron paramagnetic resonance (EPR) and time-resolved photoluminescence (TRPL) showed that the introduction of Co-Pi on ultrathin CIS surface not only increases the probability of photogenerated holes arriving the catalyst surface, but also prolongs the charge carrier's lifetime by reducing the recombination of electrons and holes. Therefore, Co-Pi/CIS exhibits a satisfactory photocatalytic H2 evolution rate of 7.28 mmol g-1 h-1 under visible light, which is superior to the pristine CIS (2.62 mmol g-1 h-1) and Pt modified CIS (3.73 mmol g-1 h-1).

Improved Thermoelectric Performance of P-type SnTe through Synergistic Engineering of Electronic and Phonon Transports.

SnTe has been regarded as a potential alternative to PbTe in thermoelectrics because of its environmentally friendly features. However, it is a challenge to optimize its thermoelectric (TE) performance as it has an inherent high hole concentration (nH∼2 × 1020 cm-3) and low mobility (µH∼18 cm2 V-1 s-1) at room temperature (RT), arising from a high intrinsic Sn vacancy concentration and large energy separation between its light and heavy valence bands. Therefore, its TE figure of merit is only 0.38 at ∼900 K. Herein, both the electronic and phonon transports of SnTe were engineered by alloying species Ag0.5Bi0.5Se and ZnO in succession, thus increasing the Seebeck coefficient and, at the same time, reducing the thermal conductivity. As a result, the TE performance improves significantly with the peak ZT value of ∼1.2 at ∼870 K for the sample (SnGe0.03Te)0.9(Ag0.5Bi0.5Se)0.1 + 1.0 wt % ZnO. This result proves that synergistic engineering of the electronic and phonon transports in SnTe is a good approach to improve its TE performance.

Manipulating Localized Vibrations of Interstitial Te for Ultra-High Thermoelectric Efficiency in p-Type Cu-In-Te Systems.

Thermoelectric materials are of imperative need on account of the worldwide energy crisis. However, their efficiency is limited by the interplay of high electrical and lower thermal conductivities, that is, the figure of merit (ZT). Owing to their unique crystal structures, Cu-In-Te-based chalcogenides are suitable for both and thus have attracted much attention recently as potential thermoelectrics. Here we explore a newly developed Cu-In-Te derivative compound Cu3.52In4.16Te8. With a proper adjustment of Cu2Te doping, this material shows an ultralow lattice thermal conductivity (κL) (0.3 WK-1m-1) and, consequently, a figure of merit (ZT) as high as 1.65(±0.15) at 815 K: the highest value reported for p-type Cu-In-Te to date. The reduction in κL is directly related to the alteration of local symmetry around the interstitial Te, resulting in an effectively optimized phonon transport through localized "rattling" of the same. Although the Hall carrier concentration reduces upon Cu2Te addition due to the unpinning of the Fermi level (EFermi) toward the conduction band minimum, the power factor remains stable. The knowledge depicted here not only demonstrates the potential of Cu3.52In4.16Te8-based alloys as a promising TE, but also provides guidelines for developing further high-performance thermoelectric materials by enhancing the electronic conductivity.

Improvement of thermoelectric performance of copper-deficient compounds Cu2.5+δ In4.5Te8 (δ = 0-0.15) due to a degenerate impurity band and ultralow lattice thermal conductivity.

Cu-In-Te ternary chalcogenides have unique crystal and band structures; hence they have received much attention in thermoelectrics. In this work we have observed an enhancement in Hall carrier concentration (n H) and ultralow lattice thermal conductivity (κ L) when Cu was added to ternary Cu2.5+δ In4.5Te8 (δ = 0-0.15) compounds. The enhancement in n H is attributed to a degenerate impurity band at the G point in the valence band maximum (VBM), while the extremely low κ L results from the increased lattice disorder. We thus obtained the minimum κ L value of only 0.23 W K-1 m-1 in the sample at δ = 0.1 and 820 K, which is in good agreement with the calculation using the Callaway model. The highest thermoelectric figure of merit ZT is 0.84 for the material at δ = 0.1, which is about 0.38 higher than that of the pristine Cu2.5In4.5Te8.

Extremely Stable Current Emission of P-Doped SiC Flexible Field Emitters.

Novel P-doped SiC flexible field emitters are developed on carbon fabric substrates, having both low Eto of 1.03-0.73 Vµm-1 up to high temperatures of 673 K, and extremely high current emission stability when subjected to different bending states, bending circle times as well as high temperatures (current emission fluctuations are typically in the range ±2.1%-3.4%).

Shape-Enhanced Photocatalytic Activities of Thoroughly Mesoporous ZnO Nanofibers.

1D mesoporous materials have attracted extensive interest recently, owning to their fascinating properties and versatile applications. However, it remains as a grand challenge to develop a simple and efficient technique to produce oxide nanofibers with mesoporous architectures, controlled morphologies, large surface areas, and optimal performances. In this work, a facile foaming-assisted electrospinning strategy with foaming agent of tea saponin is used to produce thoroughly mesoporous ZnO nanofibers with high purity and controlled morphology. Interestingly, mesoporous fibers with elliptical cross-section exhibit the significantly enhanced photocatalytic activity for hydrogen production, as compared to the counterparts with circular and rectangular cross-sections, and they also perform better than the commercial ZnO nanopowders. The unexpected shape dependence of photocatalytic activities is attributed to the different stacking modes of the mesoporous fibers, and a geometrical model is developed to account for the shape dependence. This work represents an important step toward producing thoroughly mesoporous ZnO nanofibers with tailored morphologies, and the discovery that fibers with elliptical cross-section render the best performance provides a valuable guideline for improving the photocatalytic performance of such mesoporous nanomaterials.

Electrochemical and electronic properties of LiCoO2 cathode investigated by galvanostatic cycling and EIS.

The processes of extraction and insertion of lithium ions in LiCoO(2) cathode are investigated by galvanostatic cycling and electrochemical impedance spectroscopy (EIS) at different potentials during the first charge/discharge cycle and at different temperatures after 10 charge/discharge cycles. The spectra exhibit three semicircles and a slightly inclined line that appear successively as the frequency decreases. An appropriate equivalent circuit is proposed to fit the experimental EIS data. Based on detailed analysis of the change in kinetic parameters obtained from simulating the experimental EIS data as functions of potential and temperature, the high-frequency, the middle-frequency, and the low-frequency semicircles can be attributed to the migration of the lithium ions through the SEI film, the electronic properties of the material and the charge transfer step, respectively. The slightly inclined line arises from the solid state diffusion process. The electrical conductivity of the layered LiCoO(2) changes dramatically at early delithiation as a result of a polaron-to-metal transition. In an electrolyte solution of 1 mol L(-1) LiPF(6)-EC (ethylene carbonate) :DMC (dimethyl carbonate), the activation energy of the ion jump (which is related to the migration of the lithium ions through the SEI film), the thermal activation energy of the electrical conductivity and the activation energy of the intercalation/deintercalation reaction are 37.7, 39.1 and 69.0 kJ mol(-1), respectively.