The thermal-electric performance of Bi2O2Se can be significantly improved by application of tensile strain and the Bi2O2Se monolayer has great potential as thermoelectric (TE) material.

Band degeneracy is effective in optimizing the power factors of thermoelectric (TE) materials by enhancing the Seebeck coefficients. In this study, we demonstrate this effect in model systems of layered oxyselenide family by the density functional theory (DFT) combined with semi-classical Boltzmann transport theory. TE transport performance of layered LaCuOSe and BiCuOSe are fully compared. The results show that due to the larger electrical conductivities caused by longer electron relaxation times, the n-type systems show better TE performance than p-type systems for both LaCuOSe and BiCuOSe. Besides, the conduction band degeneracy of LaCuOSe leads to a larger Seebeck coefficient and a higher optimal carrier concentration than n-type BiCuOSe, and thus a higher power factor. The optimal figure of merit (ZT) value of 1.46 for n-type LaCuOSe is 22% larger than that of 1.2 for n-type BiCuOSe. This study highlights the potential of wide band gap material LaCuOSe for highly efficient TE applications, and demonstrates that inducing band degeneracy by cations substitution is an effective way to enhance the TE performance of layered oxyselenides.

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Because of the quantum confinement effect and the interface/surface effect, the band gap of 0.8−1.5 eV for two-dimensional (2D) bismuth-based material is significantly enlarged relative to that of bulk phase materials (∼0.2 eV), which removes the inhibition effect caused by bipolar transport for the Seebeck coefficients of bulk-phase bismuth-based materials at high temperature. Therefore, the 2D bismuth-based materials exhibit huge application prospects in hightemperature thermoelectric (TE) devices, whereas their figure of merits (ZT) need to be further improved. This work reports the thermal and electrical transport properties of 2D Bi 2 TeSe 2 , a new Janus Bi 2 Te 3 -based material, from the firstprinciples calculations. Compared with Bi 2 Se 3 /Bi 2 Te 3 monolayers and corresponding Janus materials, the Bi 2 TeSe 2 monolayer exhibits a much lower lattice thermal conductivity (κ) of 0.27 W/mK at 900 K because of stronger phonon anharmonicity and higher frequency phonon scattering. In addition, because the energy pockets around the valence band maximum show convergence character, the Seebeck coefficient (SC) of the p-type system is effectively enhanced. Combined with its intrinsic high electron transport properties, a high power factor of 3.48 mW/mK 2 at 900 K is obtained for the p-type Bi 2 TeSe 2 monolayer. The ultralow κ and enhanced SC of the Bi 2 TeSe 2 monolayer eventually result in a significant optimal ZT value of 3.45 at 900 K. Thus, our study provides insights into the thermoelectric properties of the Bi 2 TeSe 2 monolayer and may open up an effective avenue for applying bismuth-based materials to a high-temperature TE field.

The first-principles calculations show that band convergence can be achieved by decreasing the interlayer distance of bilayer Bi2O2Se, which is beneficial to improve its thermoelectric performance.

The concept of element substitution was introduced with the discovery of classic semiconductors in the early 1930s. While it has been demonstrated as an effective strategy to tune the physical properties of related materials over many decades, it is physically limited to the atomic size mismatch between the dopant and the host. From another perspective, if a complex cluster can be chemically introduced into a system with a similar structure, it can be regarded as the equivalent cluster version of substitution. Complex atomic configurations usually offer more tortuous phonon paths and stronger phonon anharmonicity; however, the phenomenon of complex cluster substitution is generally less studied compared with the traditional element substitution. In this work, we take the first step using density functional theory (DFT) calculations to learn the electrical and thermal transport properties of a 1T phase transition-metal dichalcogenide (TMD) monolayer incorporated with octahedral Au6 clusters, i.e., T-Au6S2. It is found that complex cluster substitution leads to a higher phonon scattering frequency and ultralow lattice thermal conductivity (0.167 and 0.171 W/mK at 700 K along the x axis and y axis). Besides, the introduction of Au6 clusters can effectively optimize the electronic structures, balance the relationship between the Seebeck coefficient and the electrical conductivity, and thus improve the power factor. Consequently, T-Au6S2 exhibits a high thermoelectric figure of merit ZT of 3.75 (3.79) at 700 K along the x axis (y axis). Our work demonstrates that complex cluster substitution is a promising route to improve the TE conversion efficiency for low-dimensional semiconductors.

The reaction efficiency of reactants near plasmonic nanostructures can be enhanced significantly because of plasmonic effects. Herein, we propose that the catalytic activity of molecular catalysts near plasmonic nanostructures may also be enhanced dramatically. Based on this proposal, we develop a highly efficient and stable photocatalytic system for the hydrogen evolution reaction (HER) by compositing a molecular catalyst of cobalt porphyrin together with plasmonic gold nanoparticles, around which plasmonic effects of localized electromagnetic field, local heating, and enhanced hot carrier excitation exist. After optimization, the HER rate and turn-over frequency (TOF) reach 3.21 mol g−1 h−1 and 4650 h−1, respectively. In addition, the catalytic system remains stable after 45-hour catalytic cycles, and the system is catalytically stable after being illuminated for two weeks. The enhanced reaction efficiency is attributed to the excitation of localized surface plasmon resonance, particularly plasmon-generated hot carriers. These findings may pave a new and convenient way for developing plasmon-based photocatalysts with high efficiency and stability.