Aqueous synthesis of composition-tuned defects in CuInSe₂ nanocrystals for enhanced visible-light photocatalytic H₂ evolution

Abstract

The composition and defect tolerance of CuInSe₂ (CISe) quantum dots (QDs) provide a scaffold to design defects <i>via</i> tailoring the elemental ratio or distributions for boosting photocatalytic H₂ evolution (PHE). Herein, a ligand-assisted two-step aqueous method was developed to prepare defect CISe quantum dots for the first time. UV-vis, XPS, HRTEM, and HADDF investigations confirmed the typical double-absorption edges of copper vacancy defects and indium substituted at copper site defects in the structure constructed through initial synthesis tuned by Cu/In ratio and the ensued coarsening. The steady-transient PL suggested that the D-A recombination with prolonged PL lifetime dominated the emission of composition-optimized CuInSe₂ with the Cu/In ratio of 1/4 (CISe-1/4). Further transient photocurrent and electrochemical impedance spectroscopy investigations demonstrated that surface defects in the structure favor the carriers' separation/transportation. The CISe-1/4 exhibited a superior PHE rate of 722 μmol g^-1 h^-1, about 23 times higher than that of the initially synthesized CISe-1/4 nucleus (31 μmol g^-1 h^-1), with a maximum apparent quantum efficiency (AQE) of 1.3%. The analysis of energy levels and the coulombic interaction energy of electron-hole (<i>J</i> _e/h) based on Raman, extending UV-vis spectra investigations suggested that surface defects resulted in decreased <i>J</i> _e/h of CISe-1/4, favoring the enhanced PHE of this structure. This work is expected to provide a reference for designing effective non-noble metal I-III-VI photocatalysts.