Transient photovoltage study of the kinetics and synergy of electron/hole co-extraction in MoS2/Ag-In-Zn-S/carbon dot photocatalysts for promoted hydrogen production

Narrow-bandgap semiconductors play a key role in visible-light photocatalysis for solar energy conversion, where the severe charge trapping and recombination have been the main issues hindering the activity improvement. Here, MoS2 nanosheets and ferrocene-functionalized carbon dots (fCDs) were loaded on Ag-In-Zn-S quantum dots (AIZS QDs) to form ternary composite photocatalysts towards efficient electron/hole co-extraction and profound kinetics understanding of the related processes. The optimal hydrogen production rate of MoS2/AIZS/fCDs reached 8.52 mmol g−1h−1, which is dramatically higher than AIZS QDs (17.67 times), indicating the synergistic effect of electron/hole co-extraction compared to AIZS/fCDs (4.67 times) and AIZS/MoS2 (6.16 times). Transient photovoltage spectroscopy tests and the apparent kinetics analysis were carried out in terms of hydrogen production rate vs. effective surface charge carriers in the cases of pure QDs, hole extraction (binary AIZS/fCDs) and electron/hole coextraction, which indicated the hydrogen evolution reaction on the composites proceeds via the electrocatalysis based Volmer-Tafel process, involving the combination of two H* atoms to H2.