Defect-Mediated Electron-Hole Separation in One-Unit-Cell ZnIn₂S₄ Layers for Boosted Solar-Driven CO₂ Reduction

Area of Science:

• Materials Science
• Photocatalysis
• Defect Engineering

Background:

• The role of defects in electron-hole separation for photocatalysis is complex and often contradictory.
• Understanding defect types and distributions at the atomic level is crucial for optimizing material performance.

Purpose of the Study:

• To synthesize and characterize defective two-dimensional atomic layers with tunable defect concentrations.
• To elucidate the atomic-level impact of defects on electron-hole separation and photocatalytic activity.

Main Methods:

• Synthesis of defective one-unit-cell ZnIn2S4 atomic layers.
• Aberration-corrected scanning transmission electron microscopy for defect visualization.
• Positron annihilation spectrometry and electron spin resonance for defect confirmation.
• Density-functional calculations for electronic structure analysis.
• Ultrafast transient absorption spectroscopy, surface photovoltage spectroscopy, and PL spectroscopy for carrier dynamics.

Main Results:

• Successfully synthesized defective one-unit-cell ZnIn2S4 atomic layers with controlled zinc vacancy concentrations.
• Demonstrated that zinc vacancies enhance charge density and carrier transport, evidenced by ultrafast electron transfer times (~15 ps).
• Observed a ~1.7-fold increase in average recovery lifetime with higher zinc vacancy concentrations, indicating promoted carrier separation.
• Achieved a ~3.6 times higher CO2 reduction rate (33.2 μmol g-1 h-1) in ZnIn2S4 layers with rich zinc vacancies.
• Showcased excellent photocatalytic stability with negligible activity loss after 24 hours.

Conclusions:

• This study clarifies the atomic-level role of zinc vacancies in enhancing electron-hole separation in ZnIn2S4 atomic layers.
• The findings open new avenues for designing highly efficient photocatalysts for solar CO2 reduction.
• Defect engineering at the atomic level is a promising strategy for advanced energy applications.