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Using Hot Electrons and Hot Holes for Simultaneous Cocatalyst Deposition on Plasmonic Nanostructures
No full textHot electrons generated in metal nanoparticles can drive chemical reactions and selectively deposit cocatalyst materials on the plasmonic hotspots, the areas where the decay of plasmons takes place and the hot electrons are created. While hot electrons have been extensively used for nanomaterial formation, the utilization of hot holes for simultaneous cocatalyst deposition has not yet been explored. Herein, we demonstrate that hot holes can drive an oxidation reaction for the deposition of the manganese oxide (MnOx) cocatalyst on different plasmonic gold (Au) nanostructures on a thin titanium dioxide (TiO2) layer, excited at their surface plasmon resonance. An 80% correlation between the hot-hole deposition sites and the simulated plasmonic hotspot location is showed when considering the typical hot-hole diffusion length. Simultaneous deposition of more than one cocatalyst is also achieved on one of the investigated plasmonic systems (Au plasmonic nanoislands) through the hot-hole oxidation of a manganese salt and the hot-electron reduction of a platinum precursor in the same solution. These results add more flexibility to the use of hot carriers and open up the way for the design of complex photocatalytic nanostructures.</p
Insight into contraction dynamics of microwave plasmas for CO2 conversion from plasma chemistry modelling
Get PDFThis work addresses plasma chemistry in the core of a vortex-stabilized microwave discharge for CO2 conversion numerically, focusing on the pressure-dependent contraction dynamics of this plasma. A zero-dimensional model is presented for experimental conditions in a pressure range between 60 and 300 mbar and a temperature range between 3000 and 6500 K. Monte Carlo Flux simulations, which describe electron kinetics, are self-consistently coupled to the plasma chemistry model. The simulation results show that an increase in pressure is accompanied by a transition in neutral composition in the plasma core: from a significant amount of CO2 and O2 at low pressures to a O/CO/C mixture at high pressures, the composition being determined mostly by thermal equilibrium and by transport processes. The change of temperature and composition with pressure lead to higher ionisation coefficient and more atomic ion composition in the plasma core. These changes result in an increase in ionisation degree in the plasma core from 10-5 to 10-4. These factors are shown to be fundamental to drive contraction in the CO2 microwave discharge.</p
16.8% Monolithic All-Perovskite Triple-Junction Solar Cells via a Universal Two-Step Solution Process
No full textEffect of Main and Side Chain Chlorination on the Photovoltaic Properties of Benzodithiophene-Alt-Benzotriazole Polymers
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Validation of defect association energy on modulating oxygen ionic conductivity in low temperature solid oxide fuel cell
No full textThe defect association modifies the energy barrier for oxygen ion hopping between the vacancies, which is sensitive to the dopant ionic size in the CeO2-δ. Here, the work focuses on the co-dopant strategy of M0.1Sm0.1Ce0.8O2-δ (M = Yb, Gd, Sm, Nd, La) to study the defect association energy, and its subsequent effect on ionic conduction and power density. The electrolyte material with different co-dopants modifies the lattice parameter and bond length of cation–anion, which changes the defect–dopant interactions. Among the tested dopant, Nd0.1Sm0.1Ce0.8O2-δ exhibits the highest ionic conductivity of 34 mS cm−1 at 550 °C, which is nearly 2.3 times higher than the conventional Sm0.2Ce0.8O2-δ. This experimental observation validates the theoretically proposed concept of the balanced defect–dopant interactions at different sites leading to the reduction in defect association enthalpy. The experimental results were rationalized by calculating the defect association enthalpy for the co-doped system using density functional theory via one-cell method. The cell with Nd0.1Sm0.1Ce0.8O2-δ as an electrolyte shows a peak power density of 466 mW cm−2 at 550 °C, which is twice higher than the cell containing standard Sm0.2Ce0.8O2-δ electrolyte (212 mW cm−2). The results confirm that Nd0.1Sm0.1Ce0.8O2-δ is the potential electrolyte for low temperature SOFC operation. (Graphical abstract available) Erratum for Table1: The Publisher regrets that due to a production error Table 1 was incorrect in the above published article. Table 1. The ASR values obtained for button-type cells with various co-doped CeO2-δ electrolytes are also shown. The correct Table 1 is shown at DOI: https://dx.doi.org/10.1016/j.jpowsour.2020.229338</p
Incoherent and Collective Thomson Scattering for the Determination of Electron and Ion Properties in Low-Temperature Plasma
No full textIn this lecture an overview of applications of incoherent Thomson scattering (TS) as well as collective Thomson scattering (CTS) will be given. These are the most accurate methods for measuring the electron and ion properties, because the method is direct and non-intrusive. A CTS system based on the fundamental wavelength of a seeded Nd:YAG laser, being developed for the high density, low-temperature plasma of the linear plasma generator Magnum-PSI will be described also. The small Debye length of dense low temperature plasma enables application of CTS at relatively short laser wavelength. The combination of this CTS system and existing incoherent TS system enables determination of electron density and temperature as well as ion temperature and plasma velocity of the near surface plasma. In this lecture, the theoretical background and experimental challenges of the work will be given along with some examples that demonstrate the capabilities of such systems.</p
Emission spectroscopy of He lines in high-density plasmas in Magnum-PSI
No full textHelium (He) line emissions have been utilized to measure the electron density (n e) and temperature (T e), and validity checks have been conducted in various linear devices. In this study, we performed optical emission spectroscopy (OES) of He line emissions in the linear plasma device Magnum-PSI, where the used density range was 1–8 × 10 20 m −3, which was much higher than those used until now. We observed nine line emissions in the wavelength range of 388–728 nm and deduced n e and T e based on comparisons with a collisional radiative model. From the variation of the difference between the experiments and calculations, the joint probability distribution of n e and T e was deduced. We will discuss the effect of radiation trapping, in particular, based on comparisons between OES measurement results and Thomson scattering measurements
Fracture behavior of tungsten-based composites exposed to steady-state/transient hydrogen
Get PDFThe fracture behavior of plasma-facing components (PFCs) under extreme plasma-material interaction conditions is of great concern to ITER and future fusion reactors. This was explored in the current study by exposing pure tungsten (W), W-1%Ti C and W-2%Y2 O3 composites to a combined steady-state/transient hydrogen plasma up to a base surface temperature of ~2220 K, and up to 5000 transient pulses for 1000 s using the linear plasma generator Magnum-PSI. The applied heat loads were characterized by combining sheath physics, thermographic information and finite element analyses, with which the thermal stress was evaluated. Combining microstructural investigation and thermo-mechanical numerical analyses, a physical picture of fracture is developed. The transient heat loads drive surface crack initiation, whose depth can be estimated by a simple analytical model for pure tungsten, while the cooling period following the steady-state heat load induces tensile stresses, opening existing surface cracks deeper. The fracture process is mediated by the microstructure whereby the ceramic particles stabilize the microstructure but promote surface crack initiation due to suppressed plasticity at the grain boundaries and the particle-matrix interfaces. The surface cracks relieve the subsequent cycles of transient thermal stress but intensify the steady-state thermal stress, therefore, promoting deep crack propagation. These results help to understand failure mechanisms in PFCs under extreme operation conditions which are valuable for developing advanced PFCs.</p
