Regulating intragap states in colloidal quantum dots for universal photocatalytic hydrogen evolution

Abstract

Understanding and manipulating intragap states in semiconductors may enable superior solar-to-hydrogen energy conversion. The effect of intragap states on photocatalysis usually remains unclear and is sometimes contradictory. Quantum-confined colloidal quantum dots (QDs) provide a unique platform to tune the density and distribution of intragap states due to their discrete energy levels. Herein, intragap active domains, composed of Cu vacancies (VCu′) and high-valent Cu (Cu*) defect states, are constructed in copper-deficient Zn-doped CuInS2 QDs. Note that these intragap states mainly exist at in-facet and on-edge defects in QDs, being away from the valence band maximum and close to Fermi level. Steady and transient optical spectra indicate that photoactivated Cu* states serving as photoinduced absorption centers can facilitate the generation of long-lived hot electrons (ca. 85 ps) as a manifestation of phonon bottleneck. Synergistically, the VCu′ states enable the holes capture and electron-hole pairs decoupling to suppress ultrafast Auger-like hot carrier cooling (ca. 178 fs). Moreover, the on-edge defects are demonstrated to play an active role in mediating proton reduction kinetics through density functional calculation. As a result, the QDs exhibit an outstanding hydrogen generation rate of 50.4 mmol g−1 h−1 without any noble metal, meanwhile, various molecule oxidation and polymer degradation can be integrated with the hydrogen generation process.