Using the density-functional-theory-based atomic modeling, the stable interface structure and the resultant magnetocrystalline anisotropy (MCA) of the Fe/MgO(001) for magnetic random access memory have been studied. The most stable surface structure of Fe/MgO(001) thin-film system was found to be either defect free or possessing oxygen vacancies in a c(2 ×1) periodicity. The formation of the oxygen vacancies in c(2 ×1) periodicity on MgO(001) surface reduced the MCA of Fe layer from 1.38 to 0.31 meV/atom. The reduced MCA is originated from the filling of the minority states of the Fe orbital below Fermi level.
Clusters of nitrogen- and carbon-coordinated transition metals dispersed in a carbon matrix (e. g., Fe-N-C) have emerged as an inexpensive class of electrocatalysts for the oxygen reduction reaction (ORR). Here, it was shown that optimizing the interaction between the nitrogen-coordinated transition metal clusters embedded in a more stable and corrosion-resistant carbide matrix yielded an ORR electrocatalyst with enhanced activity and stability compared to Fe-N-C catalysts. Utilizing first-principles calculations, an electrostatics-based descriptor of catalytic activity was identified, and nitrogen-coordinated iron (FeN4 ) clusters embedded in a TiC matrix were predicted to be an efficient platinum-group metal (PGM)-free ORR electrocatalyst. Guided by theory, selected catalyst formulations were synthesized, and it was demonstrated that the experimentally observed trends in activity fell exactly in line with the descriptor-derived theoretical predictions. The Fe-N-TiC catalyst exhibited enhanced activity (20 %) and durability (3.5-fold improvement) compared to a traditional Fe-N-C catalyst. It was posited that the electrostatics-based descriptor provides a powerful platform for the design of active and stable PGM-free electrocatalysts and heterogenous single-atom catalysts for other electrochemical reactions.
Abstract High entropy alloys (HEAs) composed of multi‐metal elements in a single crystal structure are attractive for electrocatalysis. However, identifying the complementary functions of each element in HEAs is a prerequisite. Thus, V x CuCoNiFeMn ( x = 0, 0.5, and 1.0) HEAs are investigated to identify the active role of vanadium in improving the electrocatalytic activity for the hydrogen evolution reaction (HER). Structural studies show the successful incorporation of V in the HEA. V 1.0 CuCoNiFeMn (V 1.0 ‐HEA) shows an overpotential of 250 mV versus the reversible hydrogen electrode (at −50 mA cm −2 , 1 m KOH), which is ≈170 mV lower than that of control‐HEA (422 mV). Improves electrical conductivity and the electrochemical surface area of the V 1.0 ‐HEA accelerated HER activity. Furthermore, density functional theory calculations reveal reduced water dissociation and hydrogen adsorption energies of V 1.0 ‐HEA, resulting in the boosted HER kinetics. The effect of V incorporation on the barrier height and active sites at the surface of V 1.0 ‐HEA is schematically explained. This study can be facilitated for the development of highly active HEAs for large‐scale electrochemical water splitting.
The investigation of emerging non-toxic perovskite materials has been undertaken to advance the fabrication of environmentally sustainable lead-free perovskite solar cells. This study introduces a machine learning methodology aimed at predicting innovative halide perovskite materials that hold promise for use in photovoltaic applications. The seven newly predicted materials are as follows: CsMnCl$_4$, Rb$_3$Mn$_2$Cl$_9$, Rb$_4$MnCl$_6$, Rb$_3$MnCl$_5$, RbMn$_2$Cl$_7$, RbMn$_4$Cl$_9$, and CsIn$_2$Cl$_7$. The predicted compounds are first screened using a machine learning approach, and their validity is subsequently verified through density functional theory calculations. CsMnCl$_4$ is notable among them, displaying a bandgap of 1.37 eV, falling within the Shockley-Queisser limit, making it suitable for photovoltaic applications. Through the integration of machine learning and density functional theory, this study presents a methodology that is more effective and thorough for the discovery and design of materials.
The atomic behavior of epoxy groups on a graphene oxide sheet was observed during high thermal heat annealing using a reactive force-field based on molecular dynamics simulations. We found the oxygen-containing functional groups interplay with each other and desorbed from the graphene oxide sheet by a form of O 2 gas if they were initially in close distance. Through comparing reduction results of graphene oxide with different densities of the nearest neighboring epoxy pairs, we confirmed that the amount of released O 2 gas has a clear tendency to increase with a higher density of epoxy pairs in close distance on a graphene oxide sheet.
Solid‐state electrolytes (SSEs) are promising future power sources for electronic vehicles (EVs) and devices due to their enhanced safety features, high energy density, and nonflammability. The NASICON structure has emerged as a frontrunner in oxide‐based electrolytes, boasting high Li‐ion conductivity and air stability. Nevertheless, developing high‐performance oxide‐based electrolytes remains challenging due to their inherently hard and brittle nature, presenting obstacles to achieving an optimal interface between the cathode and anode. In this study, to overcome this issue and enhance electrochemical stability and Li‐ion conductivity, a new approach employing a hybrid solid electrolyte amalgamating polymer electrolytes with inorganic Li 1.3+ x Al 0.3− x Mg x Ti 1.7 (PO 4 ) 3 powder ( x = 0, 0.015, 0.030, 0.045, and 0.060) was investigated. Notably, employing nanosized Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP) synthesized via the sol–gel method led to a remarkable increase in ionic conductivity to 7.29 × 10 –4 S cm –1 , which was attributed to enhanced pellet density. Electrochemical analysis revealed that Li 1.345 Al 0.255 Mg 0.045 Ti 1.7 (PO 4 ) 3 exhibited superior specific capacity, stable high current density performance, and capacity recoverability compared to LATP. This pioneering study highlights the potential of hybrid solid electrolytes incorporating Mg‐doped LATP as a promising material for practical solid‐state lithium batteries.
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