In various ferroelectric-based photovoltaic materials after low-band-gap engineering, the process by which high-field polarization induces the depolarizing electric field (E dp) to accelerate the electron–hole pair separation in the visible light photocatalytic process is still a great challenge. Herein, a series of semiconducting KN-based ferroelectric catalytic materials with narrow multi-band gaps and high-field polarization capabilities are obtained through the Ba, Ni, and Bi co-doping strategy. Stable E dp caused by high-field poling enhanced the visible photocatalytic hydrogen evolution in a 0.99KN–0.01BNB sample with a narrow band gap and optimal ferroelectricity, which can be 5.4 times higher than that of the unpoled sample. The enhanced photocatalytic hydrogen evolution rate can be attributed to the synergistic effect of the significant reduction of the band gap and the high-field-polarization-induced E dp. The change in the band position in the poled sample further reveals that high-field poling may accelerate the migration of carriers through band bending. Insights into the mechanism by which catalytic activity is enhanced through high-field-polarization-induced E dp may pave the way for further development of ferroelectric-based catalytic materials in the photocatalytic field.

Van der Waals (VDW) heterostructures have attracted significant research interest due to their tunable interfacial properties and potential in a wide range of applications such as electronics, optoelectronic, and heterocatalysis. In this work, the impact of interfacial defects on the electronic structures and photocatalytic properties of hBN/MX2(M = Mo, W, and X = S, Se) are studied using density functional theory calculations. The results reveal that the band alignment of hBN/MX2 can be adjusted by introducing vacancies and atomic doping. The type-I band alignment of the host structure was maintained in the heterostructure with n-type doping in the hBN sublayer. Interestingly, the band alignment changed to the type-II heterostructrue as VB defect and p-type doping was introduced in the hBN sublayer. This could be profitable for the separation of photo-generated electron−hole pairs at the interfaces and is highly desired for heterostructure photocatalysis. In addition, two Z-type heterostructures including hBN(BeB)/MoS2, hBN(BeB)/MoSe2, and hBN(VN)/MoSe2 were achieved, showing reducing band gap and ideal redox potential for water splitting. Our results reveal the possibility of engineering the interfacial and photocatalysis properties of hBN/MX2 heterostructures via interfacial defects.

The point defect of two-dimensional hexagonal boron nitride (hBN) has recently been discovered to achieve single photon emission at room temperature, and it has become a research hotspot. Despite its important fundamental and applied research significance, the origin of the atomic structure of luminescence defects in hBN is still controversial. In this paper, first-principle calculations based on density functional theory are used to study a defect (C_N)₃V_B in the hexagonal boron nitride monolayer (hBN) where three N atoms near the B vacancy are replaced by C atoms. At the B vacancy of hBN, the three N atoms each carry an in-plane dangling bond and the corresponding unpaired electron, and the unpaired electron can be eliminated by C substitution. We systematically study the geometric structure, electronic structure and optical properties of (C_N)₃V_B defects, analyze the thermodynamic stability of defects through the calculation of the atomic structure, formation energy, and charge state of the defect, and analyze the position in the band gap and its atomic orbital contribution of defect state through energy band structure and wave function. We also analyze its optical properties through dielectric function and absorption coefficient, and predict its luminous photon energy. The results show that the defect can change from a symmetric metastable state to an asymmetric ground state structure with three C atoms connected together through atomic structure relaxation. The formation energy of asymmetric (C_N)₃V_B is 7.94 eV, which is 3.72 eV lower than that of symmetric one. The formation of defects introduces some local defect states contributed by defect dangling σ bonds and reconstructed π bonds in hBN. The defects have valence states between –2 and +2, and the thermodynamic transition energy level of asymmetric (C_N)₃V_B is higher than that of symmetric (C_N)₃V_B. In the transition from the metastable state to the ground state, these defect states can redshift the light absorption boundary of hBN, enhance the absorption intensity of visible light by hBN, and cause internal optical transitions. Among them, there is a visible light transition with an energy threshold around 2.58 eV in the asymmetry (C_N)₃V_B defect. Single boron atom vacancy defect and (C_N)₃V_B have optical transitions near infrared and ultraviolet energy, respectively. The present work will help to further understand the composition and optical properties of point defects in hBN, and provide a theoretical basis for experimentally exploring the origin and properties of the atomic structure of light-emitting point defects.

No abstract