The Z-scheme heterostructure photocatalysts have irreplaceable advantages over other heterostructures due to their ability to separate the spatial carriers and retain strong redox ability. In this study, we explored the SnS2/β-As (β-arsenene) van der Waals heterostructure with Z-scheme properties and suitable band edge positions as a potential photocatalyst for overall water splitting. Under appropriate conditions, the hydrogen evolution reaction (HER) barrier is much closer to 0. Based on the oxidation product criteria, the SnS2/β-As heterostructure photocatalyst may generate multiple end products, including •OH, H2O2, and O2. Moreover, we screen the optimal and most possible reaction pathway OER-III under irradiation among three underlying oxygen evolution reaction (OER) mechanisms, in which the intermediate species HOOH* acts as a bridge for subsequent reactions. The solar-to-hydrogen conversion efficiency of the heterostructure can reach 17.18%. This work provides new insights into designing superior photocatalysts for overall water splitting and recognizing the OER mechanism.

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The existence of Ag2Te has always been an obstacle for p-type thermoelectric material AgSbTe2 to improve its thermoelectric performance. In this work, AgSb1–x Mg x Te2 samples are synthesized by melting-slow-cooling and then spark plasma sintering (SPS). Through increasing the solubility of Ag2Te in the AgSbTe2 matrix by Mg doping, the formation of Ag2Te is inhibited. Density functional theory calculations confirm more valence bands are involved in electrical transport due to Mg doping. Therefore, the electrical conductivity of AgSb1–x Mg x Te2 samples has been greatly improved due to the reduction of Ag2Te with n-type electrical conductivity. Moreover, the downward trend of ZT, which is caused by the structural transition of Ag2Te at about 418 K, disappears. Meanwhile, lattice defects form in the AgSb0.98Mg0.02Te2 sample, and Mg doping improves the configurational entropy change, resulting in a decrease in lattice thermal conductivity over the entire temperature range of measurement. Finally, a high ZT value of 1.31 at 523 K is achieved for the AgSb0.98Mg0.02Te2 sample. This study demonstrates that Mg doping can effectively improve AgSbTe2 thermoelectric performance by inhibiting the formation of the Ag2Te impurity phase.

The lattice thermal conductivity ( κ L ) of the monolayers of partial group-VA elements and binary compounds are systemically investigated by the first-principles calculations and phonon Boltzmann transport equation (PBTE), including aW-antimonene, α-arsenene, black phosphorus, α-SbAs, α-SbP and α-AsP. The κ L values decrease with the increasing of atomic mass for these materials with similar geometry and valence structures. It is ascribed to phonon branches softening, low phonon group velocity, and large Grüneisen parameters. Due to the neutralization of phonon group velocity and phonon lifetime, κ L of binary compounds is between their corresponding elements. As the atomic radius and mass increase, the bond strength and the phonon group velocity decreases. Furthermore, the dimensionless parameter γ 2 / A , which comes from the Slack equation and only has the dependence of Grüneisen parameter, grows up with the atomic mass rising, which indicates that a larger anharmonicity is present in the heavier V-V monolayers. For SbAs and SbP compounds, the thermal conductivity anisotropy mainly results from the anisotropy of elastic coefficients along armchair and zigzag directions. Our results highlight the impact of atomic arrangement on the thermal conductivity of group VA binary compounds. This work paves a way to modulate the thermal conductivity of 2D VA elements by incorporation atoms with suitable mass and may guide to improve thermoelectrical performance via the alloying method.

n-type Mg3Bi2-based materials have been considered as a promising near-room-temperature thermoelectric material and received great attention recently. In this paper, we first investigated the thermoelectric properties of Se doped Mg3Bi2. Comparing with the undoped sample, a nearly 3-times enhancement in ZT was achieved at 300 K for Mg3Bi1.99Se0.01, which can be attributed to the significantly increasing power factor. The power factor increased from 10 µW cm−1K−2 to 30 µW cm−1K−2. The improved power factor was mainly benefited from the high Seebeck coefficient (150-160 µV K−1 at room temperature), which result from band convergence induced by Se doping. To further improve the thermoelectric performance, Mg3Bi1.99Se0.01 alloying with Mg3Sb2 have been explored. The results show that band gap of alloy increased with the increasing Sb ratio. Meanwhile, the effective scattering of phonon due to Bi/Sb disorder lead to the decrease of lattice thermal conductivity. Finally, a peak ZT of 1.3 at 525 K and average ZT of 1.02 in the temperature range of 300 - 525 K were obtained in Mg3.2Bi1.09Sb0.9Se0.01 sample.