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Direct Z-schemes for photocatalytic overall water splitting for hydrogen generation are constructed for Sc 2 CCl 2 /MoTe 2 and Sc 2 CCl 2 /Hf 2 CO 2 heterostructures on the basis of the calculated band alignment and built-in electric field. Solar-to-hydrogen efficiency (η STH ′), which is evaluated using the overpotentials of the band edges and band gaps, can reach 22.09 % for Sc 2 CCl 2 /MoTe 2 and 19.07 % for Sc 2 CCl 2 /Hf 2 CO 2. Tensile strains have little effect on η STH ′. Compressive strains substantially increase the η STH ′ of Sc 2 CCl 2 /MoTe 2 and boost that of the Sc 2 CCl 2 /Hf 2 CO 2 heterostructure only slightly. Nonadiabatic dynamics simulations reveal that the lifetime of the photogenerated electron in one of the stacking patterns of Sc 2 CCl 2 /MoTe 2 is much larger than that of the other configurations, indicating that the reduction ability of the electron is well protected. However, the interlayer electron–hole recombination in Sc 2 CCl 2 /MoTe 2 is faster than that in Sc 2 CCl 2 /Hf 2 CO 2 , implying that the Z-schemes with the former are more efficient than the Z-schemes with the latter. The hydrogen and oxidation evolution reactions with the two heterostructures are thermodynamically feasible but the reactions cannot proceed spontaneously. These findings provide a helpful guide for the development of photocatalytic materials for photocatalytic hydrogen generation from overall water splitting based on the title heterostructures. [Display omitted] • Maximum solar-to-hydrogen efficiency of the constructed schemes can reach 22.09 %. • 4 % compressive biaxial strain can boost the efficiency of Sc 2 CCl 2 /MoTe 2 to 33.77 %. • Reduction ability of SM-AA is well protected by its long electron transfer time. • Minimum Gibbs free energy of HER/OER on the heterostructures reaches 0.89/1.99 eV. [ABSTRACT FROM AUTHOR]

[Display omitted] • Based on the USPEX screening more stable SiCP 4 allotropes was obtained. • A high carrier mobility of 106 cm2 V−1 s−1 is observed for SiCP 4 allotrope. • The maximum η S T H ′ and η S T F ′ of SiCP 4 allotrope can reach 21.89% and 23.90% • Two SiCP 4 allotropes can trigger HER spontaneously. • SiCP 4 allotropes have the potential to reduce CO 2 to CH 4 or HCOOH. Two-dimensional metal-free photocatalysts are catching the attention of researchers. Here, we present several allotrope SiCP 4 monolayers with high stability, high carrier mobility, and excellent photocatalytic performance. Using a searching method based on the universal structure predictor evolutionary xtallography, together with assessing the energy and thermodynamic stabilities, and matching the potentials of band edges with the photocatalytic conditions for achieving overall water splitting, we successfully identify 5 highly favorable configurations (including the previously reported one) from a pool of 1056 allotrope SiCP 4 monolayers. The results show that the largest solar-to-hydrogen efficiency of the considered monolayers can reach 21.89 %, while a high mobility of 2.7677 × 105 cm2 V−1 s−1 is observed, both are superior to those of the previously reported one. The Gibbs free energies for hydrogen or oxygen evolutions, and CO 2 reduction reactions indicate they are thermodynamically feasible. Moreover, the hydrogen evolution reaction can proceed spontaneously with two allotrope SiCP 4 monolayers. Therefore, the newfound allotrope SiCP 4 monolayers are expected to have potential applications in the field of photocatalytic water splitting for hydrogen generation and carbon dioxide reduction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Photocatalytic Z-schemes are built for SiSe/SnSe 2 and SiSe/SnSSe heterostructures. • The STH efficiencies of the Z-schemes can reach 19.18%, 14.61%, and 14.24%. • NAMD simulations confirm photocatalytic activity of SiSe/SnSe 2 is well-protected. • Δ G s reveal both HER and OER with SiSe/SnSSe-I can spontaneously proceed. The direct Z-schemes of the photocatalytic overall water splitting with the SiSe/SnSe 2 , SiSe/SnSSe-I, and SiSe/SnSSe-II heterostructures are constructed based on the density functional theory calculations and nonadiabatic molecular dynamics (NAMD) simulations. The maximum solar-to-hydrogen efficiency (ηʹ STH) reaches 19.18% and can be promoted to 28.71% under tensile biaxial strains. NAMD simulations indicate the transfer of the electron for hydrogen evolution reaction (HER) and hole for oxygen evolution reaction (OER) for SiSe/SnSe 2 are apparently slower than those for the other two heterostructures, implicating the reduction and oxidation activities of this heterostructure are well-protected. Moreover, the shortest electron-hole recombination time is attributed to SiSe/SnSSe-I, indicating that it holds the best photocatalytic performance. Remarkably, the Gibbs free energies indicate that HER and OER with SiSe/SnSSe-I can spontaneously proceed, while OERs can but HERs cannot spontaneously proceed with the other two heterostructures. Therefore, the newfound heterostructures, especially SiSe/SnSSe-I, are promising candidates in photocatalytic overall water splitting. [ABSTRACT FROM AUTHOR]