2D/0D hierarchical heterostructures prepared via facet-selective epitaxial growth of triangular Rh nanoplates on 2H-Pd nanoparticles

Phase engineering of nanomaterials opens a promising gateway to the construction of noble metal hierarchical heterostructures in a well-defined manner. Here, by using zero-dimensional (0D) Pd nanoparticles with hexagonal close-packed (hcp, 2H type) phase, denoted as 2H-Pd, as seeds, we report a facet-selective epitaxial growth method to prepare two-dimensional (2D)/0D Pd@Rh hierarchical heterostructures, in which two parallel triangular Rh nanoplates selectively grow on two opposite (002)_h facets of 2H-Pd due to the confined growth of Rh along <002>_h direction. Systematic characterizations demonstrate that a phase transformation from 2H phase to 2H/face-centered cubic (fcc) heterophase occurs during the formation of such 2D/0D hierarchical heterostructure with the continuous growth of Rh nanoplates. The obtained 2D/0D Pd@Rh hierarchical heterostructures with a Pd/Rh atomic ratio of ∼39/61, denoted as Pd₃₉@Rh₆₁, exhibit excellent performance toward electrochemical hydrogen evolution reaction (HER) in acid electrolyte. To reach the current density of 10 mA cm^–2, the overpotential of only 21.3 mV is required for the 2D/0D Pd₃₉@Rh₆₁, which is comparable to commercial Pt/C and also among the best Rh-based HER catalysts reported until now. Key Points: The rational synthesis of novel 2D/0D Pd@Rh hierarchical heterostructures via the facet-selective epitaxial growth of Rh nanoplates on Pd nanoparticles with an unconventional 2H phase is realized. Two parallel triangular Rh nanoplates selectively grow on two opposite (002)_h facets of 2H-Pd due to the confined growth of Rh along <002>_h direction. 2D/0D Pd@Rh hierarchical heterostructures exhibit excellent performance toward electrochemical hydrogen evolution reaction in acid electrolyte.