Recently, various single-layer materials have been explored as desirable photocatalyts for water splitting. In this work, based on extensive density functional theory calculations, we examine the geometric, electronic, optical, and potential photocatalytic properties of single-layer cadmium chalcogenides (CdX sheets, X = S, Se, and Te), which are cleaved from the (001) plane of the bulk wurtzite structure. The predicted formation energies have relatively low values and a suitable substrate (i.e. graphene) that can effectively stabilize CdX sheets, which imply that the fabrication and application of CdX sheets are highly possible in experiments. The calculated band gaps, band edge positions and optical absorptions clearly reveal that CdSe and CdTe sheets are promising photocatalysts for water splitting driven by visible light. Moreover, the band gaps and band edge positions of three CdX sheets can be effectively tuned by applying biaxial strain, which then can enhance their photocatalytic performance. These theoretical findings imply that CdX sheets are promising candidates for photocatalytic water splitting.

Double-hole doping is an effective approach to engineer the band structures of semiconductors for enhancing the photoelectrochemical performance. Here, we explore the anionic monodoping (i.e. N, C, and P) and codoping (i.e. N + N, C + S, and N + P pairs) effects on the electronic structures and photocatalytic activities of ZrO2 by performing extensive density functional theory calculations. Upon anionic monodoping, several unoccupied impurity states appear within the band gap, which may trap the photogenerated carriers and then reduce the photocatalytic efficiency. Remarkably, double-hole doping via introducing three anionic (N + N), (C + S), and (N + P) codoping pairs in ZrO2 can not only effectively narrow the band gap, but can also create several fully filled delocalized intermediate bands for preventing the recombination of the photogenerated electron-hole pairs. Moreover, the band edge positions matching well with the redox potentials of water and the improved visible light absorption ability indicate that the three examined codoped ZrO2 systems are promising photocatalysts for visible light water splitting. In short, double-hole doping via anionic pairs provides an effective path to tune the huge-gap semiconductor band structures and to develop high efficient catalysts for solar-driven water splitting.

Recently, blue phosphorene (BP) has demonstrated great potential in the field of photocatalytic water splitting due to the ultrahigh carrier mobility. However, the practical application of BP as an efficient photocatalyst is greatly limited by its indirect band gap. In this work, we investigate the synergistic effect of substitutional doping and biaxial strain on the electronic and photocatalytic properties of BP using hybrid density functional calculations. The results show that As/Sb doping not only reduces the band gap of BP without introducing any midgap states but also turns it into direct band gap semiconductor, which can be ascribed to the p states of the dopants appearing around the band edges. For these As/Sb-doped BP systems, the band gaps, band edge positions, and optical absorption abilities can be further tuned by applying a biaxial strain. In particular, we predict that compressive strains are more propitious for the doped systems than the tensile strains since the requirements for water splitting are satisfied, meanwhile preserving the direct band gap characteristics.Besides, our calculations also show that the band gap and the reducing and oxidizing power of multilayer BP are highly dependent on the layer thickness. These results suggest feasible modulation strategies for enabling BP to be a visible-light-driven photocatalyst for water splitting. K E Y W O R D Sblue phosphorene, doping, indirect-to-direct band gap transition, photocatalytic water splitting, strain, carrier mobility

Designing and characterizing high-efficiency direct Z-scheme photocatalysts both from theoretical and experimental aspects still remain a big challenge. Here, based on extensive first-principles calculations combined with excited state dynamics simulations, we report that a weak van der Waals (vdW) C7N6/Sc2CCl2 heterostructure is a mediator-free direct Z-scheme photocatalyst for solar water splitting. Theoretical results clearly reveal that this heterostructure displays a nice light-harvesting performance extending to the near-infrared region. The relatively strong interfacial non-adiabatic coupling accelerates the interlayer carrier recombination in the time scale of sub-picoseconds. The well separated electrons and holes with a strong redox capacity make the hydrogen evolution reaction spontaneously occur on the C7N6 surface and the oxygen evolution reaction on the Se-doped Sc2CCl2 surface, respectively, when the proposed heterostructure is radiated with solar light.

Based on the strong metal-support interaction, designing and constructing metal-support catalyst is an effective strategy to achieve unique electronic structures and modulate interface microenvironments for improving hydrogen evolution reaction (HER)...