Yolk-shell nanostructures as an emerging photocatalyst paradigm for solar hydrogen generation

Abstract

With porous shells and mobile cores, yolk-shell nanostructures provide great structural advantage for mass transport-related applications such as photocatalysis. In this work, Au–Cu7S4 yolk-shell nanostructures are synthesized from Au–Cu2O core-shell templates. The Cu7S4 shell is then converted to CdS through a cation exchange process to produce Au–CdS yolk-shell photocatalysts for hydrogen generation. Ultrafast transient absorption and finite-difference time-domain simulation are used to investigate electronic interaction between Au nanoparticle core and the surrounding CdS shell. Additionally, a new method is presented to simulate chemical transport and quantitatively compare diffusion kinetics by monitoring mass transport through the porous CdS shell with dye molecules as optical probes. The highest hydrogen generation rate of 3390 μmol g−1 h−1, corresponding to an adequate apparent quantum yield of 4.22% at 420 nm, is achieved for Au–CdS with the largest void size. The enhancement in photocatalytic performance with increase in void size is mostly attributed to improved mass transport kinetics, with additional gains from more efficient charge transfer and stronger surface plasmon resonance-mediated near-field effects. This comprehensive study demonstrates that void size is a critical structural parameter in optimizing the performance of yolk-shell nanostructures for photocatalysis or other mass-transport related applications.