Band engineering enables highly efficient and stable photoelectrochemical hydrogen evolution

Colloidal quantum dots (QDs) are promising photosensitizers for the conversion of solar energy into electric energy or chemical fuels. Particularly, they are potentially used in photoelectrochemical (PEC) devices for the realization of solar-driven hydrogen (H2) generation because their optoelectronic properties could be tunable by controlling their size/shape/composition. However, the long-term operation stability of the PEC devices based on QDs is not good, which is strongly prohibited the potential of the QDs based PEC hydrogen production. Here, we engineer the band structure of the CdSe QDs via a Zn dopant and demonstrate a highly stable PEC devices based on CdSe/Cd1-xZnxSe QDs. Through controlling the molar ratio of Cd/Zn precursors, the Zn concentration in the shell can be finely controlled to form an alloyed shell of Cd1-xZnxSe. The alloyed shell enables the efficient hole transfer from the QDs to TiO2, benefiting from the optimization of the valence energy alignment between the core and shell. As a proof-of-concept, the PEC device based on alloyed-shell QDs achieves a current density of ∼ 13.5 mA/cm2, which is comparable to the best reported PEC devices. More importantly, the PEC devices maintained 99% of its initial current density after 10 h of continuous H2 generation under one sun illumination. Even after 50 h operation, the PEC device still keeps 65% of initial current density. The excellent long-term operation stability paves the way for the design and use of doped QDs for potential H2 production.