Progressively stimulating carrier motion over transient metal chalcogenide quantum dots towards solar-to-hydrogen conversion

Abstract

The solar-to-hydrogen conversion efficiency in photocatalytic water splitting heavily depends on the accumulation of multiple electrons at the catalytically active sites and rapid charge transport/separation. Herein, we demonstrate the construction of 0D-2D nickel-doped and Ti₃C₂T_X MXene (MN)-encapsulated transition metal chalcogenide quantum dot (TMC QD:Ni)/Ti₃C₂T_X MN heterostructures via an elaborate electrostatic self-assembly strategy. The mechanistic studies revealed that the defects induced by atomic-level foreign metal ion doping create a mid-bandgap state, which broadens the optical absorption range and extends the photo-excited carrier lifetime of the TMC QDs. The density functional calculation results verified that Ni²⁺ ion doping introduces a donor impurity level and increases the density of state at the valence band maximum, leading to a significant increase in the number of active sites and lower energy barrier for photocatalytic hydrogen evolution. The subsequent self-assembly of TMC QDs:Ni on the Ti₃C₂T_X MN framework further accelerates the charge separation and transfer due to the formation of an ideal unidirectional electron migration pathway by Ti₃C₂T_X MN, which functions as an electron-withdrawing mediator. The synergistic effect of Ni²⁺ ion doping and Ti₃C₂T_X MN decoration significantly decreases the charge transfer resistance at the photosensitizer (TMC QD)/co-catalyst (Ti₃C₂T_X MN) interface and promotes the chemisorption of protons on the catalyst surface, resulting in an excellent solar-to-hydrogen conversion efficiency. Our work provides valuable guidance for the rational design of high-efficiency photocatalysts via precise atomic-level metal ion doping and co-catalyst modulation towards emerging artificial photosynthesis.