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Thermal phonon localization, rooted in phonon wave nature, is widely observed in disordered atomic systems. Binary superlattices, with structural diversity from abundant interfaces, allow for disorder introduction by engineering interfacial structures. In this study, two different disorder entities, namely, aperiodicity (randomized layer thicknesses) and interfacial mixing, were introduced to graphene/h-BN superlattices. Molecular dynamics simulations revealed that both disordered structures can significantly reduce the thermal conductivity, with interfacial mixing more effectively impeding thermal transport. The combined effect of these disorders further decreased thermal conductivity. The underlying mechanism involves Anderson localization of phonons, demonstrated by the exponential decay of phonon transmission and suppressed phonon participation ratio. Phase-breaking interactions at higher temperatures delocalize localized modes. This study offers valuable guidance for structurally designing materials targeting low thermal conductivity through the manipulation of phonon localization. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) Janus structures, as a newly derived form of 2D materials, have recently attracted great attention due to their structural symmetry breaking along with a piezoelectric effect and potential applications in nanoscale sensors, surface acoustic waves, and energy harvesters. To date, 2D Janus materials mainly appear in the IV–VI and III–V systems but are scarce involving the IV–V elements. Hereby, utilizing first-principles structure prediction, a stable IV–V–V family of 2D Janus structure 1T-M2AB (M = Si, Ge, Sn, A/B = N, P, As) was proposed. Their electronic, elastic, and piezoelectric properties are systematically investigated and compared. The calculated piezoelectric coefficient results reveal that the 1T-Sn2NP exhibits superior piezoelectric performance with a high in-plane piezoelectric constant (−8.07 pm/V), beyond many known 2D piezoelectric materials. Three independent factors of charge density distribution, vertical mirror asymmetry, and electrostatic potential gradients were assessed, which can well account for the piezoelectric characteristics of 1T-M2AB. This work not only demonstrates the potential applications of 2D Janus 1T-M2AB monolayer in piezoelectric devices but also enriches the family of 2D Janus structures. [ABSTRACT FROM AUTHOR]

Cu-anchored N-doped carbon (C-N-Cu) catalysts have been experimentally shown to exhibit high activity for the conversion of CO2 to ethanol. It is believed that reversible Cu agglomeration on C-N-Cu catalysts under operating conditions is responsible for the high activity, but exploring their intrinsically catalytically active sites faces great challenges since the transient Cu cluster structure can't be effectively detected using in situ techniques. Here, adopting a developed constant potential method and considering the electrode potential and solvation effect, we theoretically unveil the active sites of C-N-Cu catalysts under working conditions. As a negative potential is applied on the C-N-Cu catalyst, electrons tend to occupy the anti-bonding states of Cu–N bonds, driving the leaching of Cu atoms for Cu cluster formation. An aggregated C-N-Cu5 cluster configuration is identified as natural active sites, exhibiting a well-aligned catalytical performance with experimental reports. The d-band center, charge distribution, and multiple active sites of C-N-Cu5 guarantee its configuration as a promising platform for CO2 reduction. Based on this active site, we further elucidated the reaction mechanism and key intermediates of ethanol formation on the C-N-Cu5 catalysts, revealing that the adsorbed CHO species act as the reactants for C–C coupling. [ABSTRACT FROM AUTHOR]

In this paper, we designed novel low-symmetry two-dimensional (2D) structures based on conventional XTe (X = Ge, Sn, Pb) thermoelectrics with large average atomic mass. The first-principles calculations combined with Boltzmann transport theory show that the beta-XTe exhibit good stability, high electron carrier mobility, and ultralow ΚL. The subsequent analyses show that the ultralow ΚL stems from the coexistence of resonant bonding, weak bonding, and lone-pair electrons in beta-XTe, which leads to large anharmonicities. On the other hand, the lowest energy conduction band of beta-GeTe and beta-SnTe show the convergence of the low-lying Ʃ band, which is the source of the high-power factor in the two systems. The calculated maximum ZT of beta-XTe (X = Ge, Sn, Pb) are 3.08, 1.60, and 0.57 at 300 K, respectively, which is significantly greater than that of the previously reported high-symmetry 2D alpha-XTe and the commercial thermoelectrics. We hope that this work can provide important guidance for the development of thermoelectric materials. [ABSTRACT FROM AUTHOR]

In this study, by utilizing the first-principles calculation coupled with the Boltzmann transport theory, we comprehensively study the thermoelectric (TE) properties of the Sb2C monolayer. The calculated results show that the Sb2C monolayer owns an inherent ultra-low lattice thermal conductivity of 0.88 W m−1 K−1 at 300 K, which originates from small phonon group velocities, large Grüneisen parameters, and short phonon lifetimes. The Sb2C monolayer also exhibits excellent electrical transport properties mainly due to the degeneration of the bottom conduction bands, which increases the Seebeck coefficient of the n-type doped samples and thus yields a larger power factor. Based on the extremely low lattice thermal conductivity and superior electrical transport performance, a large ZT value of 2.71 for the n-type doped Sb2C monolayer at 700 K is obtained. Our results quantify Sb2C monolayers as promising candidates for building outstanding thermoelectric devices. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) phosphorus-rich phosphides generally preserve the excellent electronic properties of phosphorene, making them promising photocatalysts for water splitting. Despite tremendous efforts in the search for potential photocatalysts in 2D phosphides, few known 2D phosphides fully meet the requirements for photocatalytic water splitting. Herein, we systemically investigate a set of penta-MP5 (M = B, Al, Ga, and In) monolayers by first-principles calculations and identify them as potential photocatalysts for water splitting. These penta-MP5 monolayers are found to feature favorable bandgaps of about 2.70 eV with appropriate band edge positions, a high carrier mobility of 1 × 104 cm−2 V−1 s−1, an excellent optical absorption coefficient (OAC) of 1 × 105 cm−1, and a good solar-to-hydrogen (STH) efficiency of 8%. Meanwhile, free energy calculations indicate that these penta-MP5 monolayers present both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) photocatalytic activities under light conditions. All these excellent properties demonstrate that penta-MP5 monolayers are suitable candidates as photocatalysts for promising applications in overall water splitting. [ABSTRACT FROM AUTHOR]