Seeded Growth and Selective Etching for Hollow Rh Nanostructures with Enhanced Performance toward Electrocatalytic Hydrogen Evolution Reaction

Hollow Rh nanostructures are highly attractive, owing to their potential to enhance catalytic performance while reducing Rh loading. However, the synthesis of hollow Rh-based nanostructures has achieved fewer successes compared to other noble metals such as Pd, Pt, Ag, and Au, primarily due to the high bond dissociation energy and surface free energy of Rh. In this work, we constructed hollow Rh nanocockleburs (Rh H-NCs) via an improved seeded growth followed by selective etching (SGSE) method. Leveraging the penta-twinned structure of Au nanobipyramids (Au NBPs), we achieved site-selective Rh deposition. Specifically, Rh atoms first nucleated at the high-energy edges and vertices owing to their lower activation barrier and then covered the facets. This process led to the formation of Au@Rh nanocockleburs (Au@Rh NCs) with a porous shell morphology. The surface porosity and shell thickness of the Rh H-NCs could be regulated by varying the amount of the Rh precursor. Our investigation into the selective etching of Au@Rh NCs reveals that the complete removal of the Au core relies on specific reaction conditions (i.e., O2 atmosphere, high concentration of CTAB, and sufficient H+) and the pivotal role of the Rh shell. The improved SGSE method was further demonstrated to be easily extended to other Au nanosystems, yielding various hollow Rh nanostructures, such as cylindrical, cubic, and spherical shapes. Benefiting from the enlarged surface area resulting from their hollow structure, the Rh H-NCs exhibited superior catalytic activity and durability for the hydrogen evolution reaction, surpassing the performance of a commercial Rh/C catalyst. This work not only provides a universal strategy for fabricating various hollow Rh nanostructures with desired shapes but also highlights their significant potential in catalytic applications.