In recent years, yolk−shell nanocrystals have become the spotlight of research worldwide because of the fascinating structural properties such as a permeable shell, an interior void space, and a movable yolk. Numerous studies have reported various compositions of yolk−shell nanocrystals. Among them, yolk−shell nanocrystals comprising metal yolk and semiconductor shells are particularly interesting because they can be geared to mass transport-related utilizations, for example, photocatalysis. We reported a sequential ion-exchange process to prepare for metal−semiconductor yolk−shell nanocrystals comprising Au yolk associated with various semiconductor shells. The synthetic procedures involved delicate sulfidation on a Au@Cu 2 O core−shell nanocrystal template, followed by a kinetically controlled cation-exchange reaction that enabled the conversion of the shell composition into various metal sulfides. Four representative yolk−shell nanocrystal samples, including

In this work, we demonstrated the practical use of Au@Cu2O core–shell and Au@Cu2Se yolk–shell nanocrystals as photocatalysts in photoelectrochemical (PEC) water splitting and photocatalytic hydrogen (H2) production. The samples were prepared by conducting a sequential ion-exchange reaction on a Au@Cu2O core–shell nanocrystal template. Au@Cu2O and Au@Cu2Se displayed enhanced charge separation as the Au core and yolk can attract photoexcited electrons from the Cu2O and Cu2Se shells. The localized surface plasmon resonance (LSPR) of Au, on the other hand, can facilitate additional charge carrier generation for Cu2O and Cu2Se. Finite-difference time-domain simulations were carried out to explore the amplification of the localized electromagnetic field induced by the LSPR of Au. The charge transfer dynamics and band alignment of the samples were examined with time-resolved photoluminescence and ultraviolet photoelectron spectroscopy. As a result of the improved interfacial charge transfer, Au@Cu2O and Au@Cu2Se exhibited a substantially larger photocurrent of water reduction and higher photocatalytic activity of H2 production than the corresponding pure counterpart samples. Incident photon-to-current efficiency measurements were conducted to evaluate the contribution of the plasmonic effect of Au to the enhanced photoactivity. Relative to Au@Cu2O, Au@Cu2Se was more suited for PEC water splitting and photocatalytic H2 production by virtue of the structural advantages of yolk–shell architectures. The demonstrations from the present work may shed light on the rational design of sophisticated metal–semiconductor yolk–shell nanocrystals, especially those comprising metal selenides, for superior photocatalytic applications.

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