Along the way to designing of new cathode materials for solid oxide fuel cells (SOFCs), an understanding of the mechanism of oxygen reduction reaction (ORR) plays a key role, especially the interaction between O 2 molecule and surface of cathode. Recently, La 2 NiO 4 with K 2 NiF 4 -type structure has been developed, and it has received great attention as an oxygen sensor and a potential cathode for SOFCs. However, the chemical activity of La 2 NiO 4 , in particular, the ORR on the surface, has not been studied so thoroughly. In this report, we present the structural and energetic results of O 2 adsorbed onto the perfect and defective La 2 NiO 4 (100) surface to elucidate the interaction mechanism between O 2 molecule and cathode using atomistic computer simulation based on density functional theory. The results show that the surface structure and the adsorbed configurations are vital for O 2 adsorption. and activation. The adsorbed species on the perfect surface are energetically less favorable than defective surface. The Ni site is preferred with adsorption energy of −1.25 (Ni-super) and −1.80 eV (Ni-per), much higher than these of La site, supporting the fact that transition-metal cations are more active than lanthanon metals in K 2 NiF 4 -type compounds. Surface oxygen vacancy is found to enhance the adsorption energy of O 2 molecule on the La 2 NiO 4 (100) surface; in addition, oxygen vacancy can be an active site in O 2 adsorption. The most stable configuration is Ni−O−Ni mode, with the highest adsorption energy being −2.61 eV. This can be confirmed by the analysis of the local density of states (LDOS) and the difference electron density. These results have an important implication for understanding the ORR on La 2 NiO 4 (100) surface.
the SCAN-rVV10 density functional, the electrochemical properties
of bare Mo-based ordered double-transition metal MXenes (Mo2MC2, M = Sc, Ti, V, Zr, Nb, Hf, Ta) as aluminum-ion battery
anode materials are studied. By calculating the average adsorption
energy for each layer in a symmetric multilayer adsorption configuration,
we find that all investigated MXene structures could adsorb three
layers of Al atoms on both upper and lower surfaces, leading to the
high theoretical capacities ranging from 888.98 mAh g–1 (Mo2TaC2) to 1170.33 mAh g–1 (Mo2ScC2). The formation of a multilayer adsorption
configuration for Al atoms on Mo-based MXenes is mainly attributed
to the gradual decreasing of the valence charge transfer from the
adsorption layer to the substrate. Then, the CI-NEB method is used
to assess the diffusion performance of Al atoms adsorbed on MXenes
for energy favorable zig-zag like migration pathways. It is revealed
that the migration energy barrier is no larger than 0.20 eV for all
seven Mo-based MXenes. Therefore, the intrinsic Mo-based double-transition
metal MXenes are promising anode materials possessing both high energy
storage density and fast ion diffusion dynamics for Al-ion batteries.
Two mechanisms have been proposed to explain the suppression of space charge in polyethylene by the addition of nano-fillers, i.e. an interface change that reduces charge injection and a bulk modification that affects charge migration and recombination. The relative importance of each mechanism in Low Density Polyethylene (LDPE) nanocomposites is investigated by the measurement of space charge in samples of doublelayer and triple-layer structures. The experimental results show that the nano-fillers reduce charge injection, but do not entirely eliminate the space charge. Bulk changes also play an important role in space charge suppression. The space charge near the interface between the unfilled LDPE and nanocomposites shows a surface charge at 20 C, but at 60 C a bipolar blocking phenomenon is observed in some circumstances. It is shown that these space charge distributions can be reproduced using a band theory approach with the assumption that the introduction of deep traps by nano-fillers raises the Fermi level of the nanocomposite towards the conduction level.
The vacuum surface flashover characteristic of solid material under steep pulse severely restricts the structure and performance of pulsed-power devices; and with excellent performance in insulation and mechanical strength, epoxy resin has been widely employed in pulse equipment; moreover, the accumulation of surface charge not only enhances the electric field but also affects the movement of the charge produced during flashover as to influence the flashover voltage, so the study of vacuum surface flashover characteristic and surface charge property of epoxy resin under steep pulse is of great significance. Using the 15ns/1070ns (referring to the rise time and the half-height width time of the pulse) single-pulse generator, remaining the vacuum on the level of 5E-3Pa, the surface flashover voltage of epoxy resin at different flashover times are tested in this article, and applying a tridimensional regulating mechanism and a surface potentiometer, the surface charge distribution after certain flashover times is measured at the meantime under the same vacuum degree. Via injecting surface charges in different polarize and magnitude to epoxy resin sample, the article studies the function mechanism of surface charge accumulation on the vacuum flashover voltage of epoxy resin under steep pulse.
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