Direct Z-Scheme Photocatalytic System: Insights into the Formative Factors of Photogenerated Carriers Transfer Channel from Ultrafast Dynamics

Abstract

The direct Z-scheme photocatalytic heterojunction, possessing type II band alignments but simultaneously realizing the spatial separation of photogenerated electrons and holes (PEHs) and the well-preserved strong redox ability, is a promising strategy for solving energy and environmental issues. However, the conventional method of solely relying on the direction of interfacial electric field (IEF) to determine the Z-scheme is often different with experiments. Properly evaluating and constructing the direct Z-scheme remain limited. Herein, combining hybrid density functional theory and excited state ultrafast dynamics simulation, we find that the formative factor of the Z-scheme path comes from two aspects by systematically exploring a series of prototypical heterojunctions taking X2Y3 ferroelectrics (X: Al, Ga, In. Y: S, Se, Te) and BCN semiconductors. On the one hand, the interlayer recombination of PEHs with weak redox ability can be significantly promoted by the IEF. On the other hand, for PEHs with strong redox ability, the weak nonadiabatic coupling of interface transfer channel plays a key role in preserving the high activity of PEHs, which can extend the reacting time of PEHs from femtosecond to hundreds of nanosecond scale. This study deepens the understanding of Z-scheme formation and can accelerate the design of direct Z-scheme photocatalysts.

Metal-Free Carbon Nitride Nanosheet Supported the Pentacoordinated Silicon Intermediates for Photocatalytic Overall Water Splitting

“…According to these dynamic processes, the lifetime of photogenerated electrons and holes can be roughly estimated to be about 5.19 and 47.99 ns, respectively, by employing the exponential function P(t) = exp(−t/τ). 56 Although the lifetime of the photogenerated electron is shorter than that of the hole, the time scale is still in nanoseconds, which is consistent with that of defects suppressing the recombination, such as the lifetime of photogenerated carriers for Se vacancies in WSe 2 nanosheet (∼3 ns). 57 In contrast, for defects such as the fast recombination centers, the lifetime of photogenerated carriers is generally in the picosecond scale, such as W vacancies and Se W antisites in WSe 2 nanosheet.…”

“…After 10 ns, almost all photogenerated electrons are transferred to the impurity state, whereas only around 20% of photogenerated holes are captured by the impurity state (see Figure b). According to these dynamic processes, the lifetime of photogenerated electrons and holes can be roughly estimated to be about 5.19 and 47.99 ns, respectively, by employing the exponential function P ( t ) = exp­(− t /τ) . Although the lifetime of the photogenerated electron is shorter than that of the hole, the time scale is still in nanoseconds, which is consistent with that of defects suppressing the recombination, such as the lifetime of photogenerated carriers for Se vacancies in WSe 2 nanosheet (∼3 ns) .…”

Engineering interface structures for heterojunction photocatalysts

“…Compared with single doping, doping two components into the heterojunction interface at the same time can generally obtain the synergistic effect of bimetallic ions. 104 In addition, co-doping at the heterojunction interface can cause lattice distortion, crystal morphology change, overpotential and band gap value change. Meng et al 105 prepared nitrogen (N) and sulfur (S) codoping black TiO 2 (NS-BT) for broadening the visible light response range of TiO 2 , and further successfully constructed with g-C 3 N 4 to a CN/NS-BT heterostructure.…”

Kinetically and Thermodynamically Favorable Ni–Al Layered Double Hydroxide/Ni-Doped Zn0.5Cd0.5S S-Scheme Heterojunction Triggering Photocatalytic H2 Evolution

“…An appealing and sustainable approach for converting renewable solar energy into chemical energy that can be stored is called photocatalytic H 2 evolution (PHE). − Designing and constructing comparable photocatalysts are crucial steps in PHE. Very recently, layered double hydroxide (LDH) materials have emerged as promising photocatalysts for H 2 evolution. − Nevertheless, the low availability of photogenerated carriers of the single-phase LDH-based photocatalysts seriously limits their application. − To solve these issues, a multitude of strategies, including interfacial engineering, , defect control, , element doping, , morphology regulation, and construction of heterojunctions, , have been proposed to accelerate the separation and migration of carriers. It is widely known that kinetics and thermodynamics are greatly important for exploring the photocatalytic reaction, and the improvement in photocatalytic activity depends on not only kinetics but also the thermodynamic level .…”