Evolution of Hollow CuInS₂ Nanododecahedrons via Kirkendall Effect Driven by Cation Exchange for Efficient Solar Water Splitting

Hollow-structured semiconductor nanocrystals (NCs) have aroused tremendous research interest because of their compelling structure-related properties that can facilitate the development of many important applications including solar water splitting. However, the creation of multicomponent semiconductor NCs (such as I-III-VI₂ and I₂-II-IV-VI₄ semiconductors) possessing a hollow architecture still remains a great challenge because of the difficulty in balancing the reactivities of multiple precursors. In this study, we report an effective strategy to prepare hollow CuInS₂ nanododecahedrons featuring high uniformity in morphology and composition, based on the Kirkendall effect driven by the cation exchange between Cu⁺ and In³⁺ using Cu_2-xS nanododecahedrons as templates. The unequal diffusion rates of cations result in an inward flux of vacancies favorably along the (0 16 0) facets of Cu_2-xS dodecahedrons, forming a Cu_2-xS@CuInS₂ core-shell intermediate with striped voids in the core region. Optical absorption studies and photoelectrochemical measurements imply that the increase in the hollowing degree of the NCs benefits enhanced light harvesting and separation of photogenerated charge carriers. As a result, the obtained hollow CuInS₂ nanododecahedrons present a high activity in photocatalytic hydrogen evolution, much superior to previously reported CuInS₂ photocatalysts with different architectures. We envision that the multifarious morphologies attainable for the Cu_2-xS NC templates and the advantages of Cu⁺ for cation exchange can make this method adaptable to a vast variety of previously intractable structures and compositions.