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Abstract 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 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 h direction. 2D/0D Pd@Rh hierarchical heterostructures exhibit excellent performance toward electrochemical hydrogen evolution reaction in acid electrolyte.

Given the high energy density and eco-friendly characteristics, lithium-carbon dioxide (Li-CO2) batteries have been considered to be a next-generation energy technology to promote carbon neutral and space exploration. However, Li-CO2 batteries suffer from sluggish reaction kinetics, causing large overpotential and poor energy efficiency. Here, we observe enhanced reaction kinetics in aprotic Li-CO2 batteries with unconventional phase 4H/face-centered cubic (fcc) iridium (Ir) nanostructures grown on gold template. Significantly, 4H/fcc Ir exhibits superior electrochemical performance over fcc Ir in facilitating the round-trip reaction kinetics of Li+-mediated CO2 reduction and evolution, achieving a low charge plateau below 3.61 V and high energy efficiency of 83.8%. Ex situ/in situ studies and theoretical calculations reveal that the boosted reaction kinetics arises from the highly reversible generation of amorphous/low-crystalline discharge products on 4H/fcc Ir via the Ir-O coupling. The demonstration of flexible Li-CO2 pouch cells with 4H/fcc Ir suggests the feasibility of using unconventional phase nanomaterials in practical scenarios. [ABSTRACT FROM AUTHOR]

Doped nanoparticles (especially bimetal doped nanoparticles) have attracted extensive interest not only for fundamental scientific research but also for application purposes. However, their indefinite composition (structure) and broad distribution hinder an insightful understanding of the interaction between these invasive metals in bimetal doped nanoparticles. Fortunately, atom-precise bimetal doped ultrasmall nanoparticles (nanoclusters) provide opportunities to obtain such insights. However, atom-precise trimetal nanoclusters and their structures have rarely been reported. Here, we successfully dope thiolated Au25 nanoclusters with Hg and Ag successively by using a biantigalvanic reduction method. We then fully characterize the as-obtained trimetal nanoclusters using multiple techniques (including single-crystal X-ray crystallography), and we demonstrate that the mercury and silver dopings exhibit not only a synergistic but also a counteractive influence on some of the physicochemical properties of Au25. [ABSTRACT FROM AUTHOR]

Controlling the bimetal nanoparticle with atomic monodispersity is still challenging. Herein, a monodisperse bimetal nanoparticle is synthesized in 25% yield (on gold atom basis) by an unusual replacement method. The formula of the nanoparticle is determined to be Au24Hg1(PET)18 (PET: phenylethanethiolate) by high-resolution ESI-MS spectrometry in conjunction with multiple analyses including X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). X-ray single-crystal diffraction reveals that the structure of Au24Hg1(PET)18 remains the structural framework of Au25(PET)18 with one of the outer-shell gold atoms replaced by one Hg atom, which is further supported by theoretical calculations and experimental results as well. Importantly, differential pulse voltammetry (DPV) is first employed to estimate the highest occupied molecular orbit (HOMO) and the lowest unoccupied molecular orbit (LUMO) energies of Au24Hg1(PET)18 based on previous calculations. [ABSTRACT FROM AUTHOR]