High-entropy alloy nanocrystals boosting photocatalytic hydrogen evolution coupled with selective oxidation of cinnamyl alcohol

Photocatalysis provides a promising solution to the worldwide shortages of energy and industrially important raw materials by utilizing sunlight for coupled hydrogen (H-2) production with controllable organic transformation. Herein, we demonstrate that PtFeNiCoCu high-entropy alloy (HEA) nanocrystals can act as efficient cocatalysts for H-2 evolution coupled with selective oxidation of cinnamyl alcohol to cinnamaldehyde by cubic cadmium sulfide (CdS) quantum dots (QDs) with uniform sizes of 4.0 +/- 0.5 nm. HEA nanocrystals were prepared via a simple solvothermal approach, and were successfully integrated with CdS QDs by an electrostatic self-assembly method to construct HEA/CdS composites. The optimized HEA/CdS sample presented an enhanced photocatalytic H-2 production rate of 7.15 mmol g(-1) h(-1), which was 13 times that of pure CdS QDs. Moreover, a cinnamyl alcohol conversion of 96.2% with cinnamaldehyde selectivity of 99.5% was achieved after photoreaction for 3 h. The integration of HEA with CdS QDs extended the optical absorption edge from 475 to 484 nm. From d-band center analysis, Pt atoms in the HEA are the active sites for H-2 evolution, exhibiting higher catalytic activity than pure Pt. Meanwhile, the band structure of the CdS QDs enables the oxidative transformation of cinnamyl alcohol to cinnamaldehyde with high selectivity. Moreover, femtosecond transient absorption spectroscopy shows that HEA can significantly promote the separation of photogenerated carriers in CdS, which is vital for achieving enhanced photocatalytic activity. This work inspires atomic-level design of photocatalytic materials for coordinated production of green energy carriers and value-added products. Published by Elsevier B.V. All rights reserved.