ABSTRACT
Transition metal dichalcogenides have been the most attractive two-dimensional layered materials for electrocatalytic hydrogen evolution due to their unique structure and multi-phase electronic states. However, the enhancement of the WSe2 electrocatalytic hydrogen evolution reaction (HER) performance by bimetal co-doping has been rarely reported. Herein, the NiMo-WSe2 catalyst has been synthesized by a one-step hydrothermal reaction, with lower overpotentials of 177 and 188 mV at a current density of 10 mA cm-2 in 0.5 M H2SO4 and 1 M KOH, respectively. The large specific surface area and thinner edge morphology provide more active sites for hydrogen production, thereby significantly improving the charge transfer kinetics. Density functional theory calculation results show that under acidic conditions the ΔGH* values of NiMo-WSe2 with different structures and hydrogen adsorption sites are also different, when the hydrogen adsorption site was located at the top of the Se-Ni bond, the meta NiMo-WSe2 has a ΔGH* value (-0.04 eV) that is closest to 0. Meanwhile, NiMo-WSe2 (meta) also has a minimum of ΔGH* under alkaline conditions. DOS confirmed that Ni doping has a large impact on the electronic states at the WSe2 Fermi level, while NiMo co-doping greatly reduces the potential energy barrier of the HER reaction, jointly increasing the current density, and thus improving the HER performance.
ABSTRACT
Optically transparent microwave absorbers have been widely reported for electromagnetic stealth applications over the past few years, but developing ultra-wideband absorbers with high angular stability remains challenging. In this work, an absorber comprising a double-layer polymethylpentene (TPX) block and indium tin oxide (ITO) films has been designed, fabricated, and measured, respectively. Firstly, an impedance layer with novel coupled hexagonal combined elements is exploited to achieve ultra-wideband absorption. Secondly, to provide the optimal reflection response for high angular incidences, the TPX block with the lower permittivity is initially employed in the compensation and substrate layers. Finally, the experimental results agreed with simulation ones illustrate the excellent performance is concurrently achieved, including a 90% absorption bandwidth within 2.53-8.94 (111.8%), high angular stability (60°), and the high light transmittance (70.7%).
ABSTRACT
We apply two sparse reconstruction techniques, the least absolute shrinkage and selection operator (LASSO) and the sparse exponential mode analysis (SEMA), to two-dimensional (2D) spectroscopy. The algorithms are first tested on model data, showing that both are able to reconstruct the spectra using only a fraction of the data required by the traditional Fourier-based estimator. Through the analysis of the sparsely sampled experimental fluorescence-detected 2D spectra of LH2 complexes, we conclude that both SEMA and LASSO can be used to significantly reduce the required data, still allowing one to reconstruct the multidimensional spectra. Of the two techniques, it is shown that SEMA offers preferable performance, providing more accurate estimation of the spectral line widths and their positions. Furthermore, SEMA allows for off-grid components, enabling the use of a much smaller dictionary than that of the LASSO, thereby improving both the performance and the lowering of the computational complexity for reconstructing coherent multidimensional spectra.
