The crystal phase-based heterostructures of noble metal nanomaterials are of great research interest for various applications, such as plasmonics and catalysis. However, the synthesis of unusual ...crystal phases of noble metals still remains a great challenge, making the construction of heterophase noble metal nanostructures difficult. Here, we report a one-pot wet-chemical synthesis of well-defined heterophase fcc-2H-fcc gold nanorods (fcc: face-centred cubic; 2H: hexagonal close-packed with stacking sequence of "AB") at mild conditions. Single particle-level experiments and theoretical investigations reveal that the heterophase gold nanorods demonstrate a distinct optical property compared to that of the conventional fcc gold nanorods. Moreover, the heterophase gold nanorods possess superior electrocatalytic activity for the carbon dioxide reduction reaction over their fcc counterparts under ambient conditions. First-principles calculations suggest that the boosted catalytic performance stems from the energetically favourable adsorption of reaction intermediates, endowed by the unique heterophase characteristic of gold nanorods.
Heterostructured, including heterophase, noble-metal nanomaterials have attracted much interest due to their promising applications in diverse fields. However, great challenges still remain in the ...rational synthesis of well-defined noble-metal heterophase nanostructures. Herein, we report the preparation of Pd nanoparticles with an unconventional hexagonal close-packed (2H type) phase, referred to as 2H-Pd nanoparticles, via a controlled phase transformation of amorphous Pd nanoparticles. Impressively, by using the 2H-Pd nanoparticles as seeds, Au nanomaterials with different crystal phases epitaxially grow on the specific exposed facets of the 2H-Pd, i.e., face-centered cubic (fcc) Au (fcc-Au) on the (002)h facets of 2H-Pd while 2H-Au on the other exposed facets, to achieve well-defined fcc-2H-fcc heterophase Pd@Au core–shell nanorods. Moreover, through such unique facet-directed crystal-phase-selective epitaxial growth, a series of unconventional fcc-2H-fcc heterophase core–shell nanostructures, including Pd@Ag, Pd@Pt, Pd@PtNi, and Pd@PtCo, have also been prepared. Impressively, the fcc-2H-fcc heterophase Pd@Au nanorods show excellent performance toward the electrochemical carbon dioxide reduction reaction (CO2RR) for production of carbon monoxide with Faradaic efficiencies of over 90% in an exceptionally wide applied potential window from −0.9 to −0.4 V (versus the reversible hydrogen electrode), which is among the best reported CO2RR catalysts in H-type electrochemical cells.
Phase engineering of nanomaterials (PEN) offers a promising route to rationally tune the physicochemical properties of nanomaterials and further enhance their performance in various applications. ...However, it remains a great challenge to construct well‐defined crystalline@amorphous core–shell heterostructured nanomaterials with the same chemical components. Herein, the synthesis of binary (Pd‐P) crystalline@amorphous heterostructured nanoplates using Cu3−χP nanoplates as templates, via cation exchange, is reported. The obtained nanoplate possesses a crystalline core and an amorphous shell with the same elemental components, referred to as c‐Pd‐P@a‐Pd‐P. Moreover, the obtained c‐Pd‐P@a‐Pd‐P nanoplates can serve as templates to be further alloyed with Ni, forming ternary (Pd‐Ni‐P) crystalline@amorphous heterostructured nanoplates, referred to as c‐Pd‐Ni‐P@a‐Pd‐Ni‐P. The atomic content of Ni in the c‐Pd‐Ni‐P@a‐Pd‐Ni‐P nanoplates can be tuned in the range from 9.47 to 38.61 at%. When used as a catalyst, the c‐Pd‐Ni‐P@a‐Pd‐Ni‐P nanoplates with 9.47 at% Ni exhibit excellent electrocatalytic activity toward ethanol oxidation, showing a high mass current density up to 3.05 A mgPd−1, which is 4.5 times that of the commercial Pd/C catalyst (0.68 A mgPd−1).
Binary (Pd‐P) and ternary (Pd‐Ni‐P) nanoplates, both with crystalline@amorphous core–shell nanostructures, are synthesized using Cu3−χP nanoplates as templates. The obtained c‐Pd‐Ni‐P@a‐Pd‐Ni‐P heterostructured nanoplates exhibit superior electrocatalytic performance toward the ethanol oxidation reaction in alkaline media compared to c‐Pd‐P@a‐Pd‐P heterostructured nanoplates and commercial Pd/C catalysts.
Crystal phase engineering of noble-metal-based alloy nanomaterials paves a new way to the rational synthesis of high-performance catalysts for various applications. However, the controlled ...preparation of noble-metal-based alloy nanomaterials with unconventional crystal phases still remains a great challenge due to their thermodynamically unstable nature. Herein, we develop a robust and general seeded method to synthesize PdCu alloy nanomaterials with unconventional hexagonal close-packed (hcp, 2H type) phase and also tunable Cu contents. Moreover, galvanic replacement of Cu by Pt can be further conducted to prepare unconventional trimetallic 2H-PdCuPt nanomaterials. Impressively, 2H-Pd67Cu33 nanoparticles possess a high mass activity of 0.87 A mg–1 Pd at 0.9 V (vs reversible hydrogen electrode (RHE)) in electrochemical oxygen reduction reaction (ORR) under alkaline condition, which is 2.5 times that of the conventional face-centered cubic (fcc) Pd69Cu31 counterpart, revealing the important role of crystal phase on determining the ORR performance. After the incorporation of Pt, the obtained 2H-Pd71Cu22Pt7 catalyst shows a significantly enhanced mass activity of 1.92 A mg–1 Pd+Pt at 0.9 V (vs RHE), which is 19.2 and 8.7 times those of commercial Pt/C and Pd/C, placing it among the best reported Pd-based ORR electrocatalysts under alkaline conditions.
The electrochemical CO2 reduction reaction (CO2RR) offers a green and sustainable process to convert CO2 into valuable chemical stocks and fuels. Metal is one of the most promising types of catalysts ...to drive an efficient and selective CO2RR. The catalytic performance of metal nanocatalysts is strongly dependent on their structural features. Recently, phase engineering of nanomaterials (PEN) has emerged as a prominent tactic to regulate the catalytic performance of metal nanocatalysts for the CO2RR. A broad range of metal nanocatalysts with conventional and unconventional crystal phases has been developed, and remarkable achievements have been made. This review summarizes the most recent developments in phase engineering of metal nanocatalysts for the electrochemical CO2RR. We first introduce the different crystal phases of metal nanocatalysts used in the CO2RR and then discuss various synthetic strategies for unconventional phases of metal nanocatalysts. After that, detailed discussions of metal nanocatalysts with conventional and unconventional phases, including amorphous phases, are presented. Finally, the challenges and perspectives in this emerging area are discussed.
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•Phase engineering of nanomaterials (PEN) emerges as a promising tactic to regulate their electrocatalytic performances.•Recent development in phase engineering of metal nanocatalysts for electrochemical CO2 reduction reaction was summarized.•Challenges and perspectives towards phase engineering of metal nanocatalysts for electrochemical CO2 reduction were proposed.
In this work, the effects of various additives on the AlN conversion fraction, weight loss, phase compositions and surface morphology during the carbothermal synthesis of spherical AlN granules were ...investigated in detail. The results inferred that additives played an important role in the improvement of nitridation rate, the formation of spherical morphology and the growth of particle size. The simultaneous addition of CaF2 and YF3 resulted in the highest nitridation rate in all samples, while excessive CaF2 appeared to retard the nitridation process at a particular temperature. However, Ca-aluminates forming in the synthesis process tended to be reduced and further volatilized at high temperature. Furthermore, by analyzing the weight loss during the carbothermal reduction-nitridation process, the reaction mechanisms in the systems using different additives were also attentively disclosed.
•The nitridation rate could be changed by using various additives.•Simultaneous addition of CaF2 and YF3 results in the highest nitridation rate.•Ca-aluminates tended to be reduced and vaporized at high temperature.
Epitaxial growth is one of the most commonly used strategies to precisely tailor heterostructures with well-defined compositions, morphologies, crystal phases, and interfaces for various ...applications. However, as epitaxial growth requires a small interfacial lattice mismatch between the components, it remains a challenge for the epitaxial synthesis of heterostructures constructed by materials with large lattice mismatch and/or different chemical bonding, especially the noble metal-semiconductor heterostructures. Here, we develop a noble metal-seeded epitaxial growth strategy to prepare highly symmetrical noble metal-semiconductor branched heterostructures with desired spatial configurations, i.e., twenty CdS (or CdSe) nanorods epitaxially grown on twenty exposed (111) facets of Ag icosahedral nanocrystal, albeit a large lattice mismatch (more than 40%). Importantly, a high quantum yield (QY) of plasmon-induced hot-electron transferred from Ag to CdS was observed in epitaxial Ag-CdS icosapods (18.1%). This work demonstrates that epitaxial growth can be achieved in heterostructures composed of materials with large lattice mismatches. The constructed epitaxial noble metal-semiconductor interfaces could be an ideal platform for investigating the role of interfaces in various physicochemical processes.
In this study, micron-sized spherical AlN granules were delicately synthesized by carbothermal reduction–nitridation (CRN) route with the aid of Y2O3 additive. The effects of synthesis parameters and ...Y2O3 content on the nitridation rate, particle size and especially on the surface morphology were systematically investigated. The results showed that the reduction and nitridation of intermediate Y-aluminates were extremely significant to promote the formation of micro-sized spherical AlN granules by improving the nitridation rate, increasing the grain size, providing the spherical morphology and promoting the uniform growth of AlN granules. Furthermore, the elevated N2 gas pressure, high reaction temperature also made contribution to the formation of spherical morphology and large particle size. Based on the experimental results, the underlying reaction mechanism in the carbothermal synthesis of spherical AlN granules with Y2O3 was attentively proposed.
Conspectus Two-dimensional (2D) nanomaterials have attracted increasing research interest since mechanically exfoliated graphene was obtained in 2004. The ultrathin thickness and relatively large ...lateral size of 2D nanomaterials render them various intriguing properties such as compelling electronic properties, ultrahigh specific surface area, excellent mechanical properties, and so on. A wide range of 2D nanomaterials, including graphene and its derivatives, transition metal dichalcogenides (TMDs), metals, etc., have been prepared with different compositions, structures and (crystal) phases. Simultaneously, extensive research efforts have been devoted to exploring the potential applications of these 2D nanomaterials with enhanced performances. Hybridization of two or more nanomaterials to prepare novel composites could efficiently integrate the advantages of the individual components and thus optimize their performances for specific applications. Among various hybridization approaches, the templated synthesis method, i.e., using a presynthesized nanomaterial as a template to direct the growth of a secondary nanostructure, provides an efficient way to prepare composites with high controllability. The ultrathin thickness, large specific surface area, and versatile physiochemical properties of 2D nanomaterials make them ideal templates for constructing composites with desired structures, properties, and functions. Until now, various 2D nanomaterials have been used as templates to grow different kinds of nanomaterials, including metals, metal oxides, metal chalcogenides, metal–organic frameworks (MOFs), etc., to form 2D nanomaterial-templated composites that show potentials in various applications. In this Account, we first briefly introduce the general research background of 2D nanomaterials and the motivation for the preparation of 2D nanomaterial-templated composites. Then we summarize our progress and some other representative work on 2D nanomaterial-templated composites, with a particular emphasis on graphene-templated composites, 2D TMD-templated composites, and 2D metal-templated composites. Specifically, representative examples of the graphene-templated zero-dimensional (0D), one-dimensional (1D), and 2D composites and the emerging graphene-templated van der Waals heterostructures are described. Subsequently, typical 2D TMD-templated composites such as metal oxides, metals, and metal chalcogenides are also presented. In addition, we introduce 2D metal-templated composites and highlight that the crystal phase of the 2D metal template can play an important role in the controlled synthesis of heterostructures. Other composites constructed using 2D metal oxides, metal hydroxides, metal sulfides, and MOFs as templates are also introduced. After that, we demonstrate the potential applications of 2D nanomaterial-templated composites, including electrocatalysis, electronic devices, batteries, and so on. Finally, after a brief summary, our personal insights on the challenges and future research directions in this emerging field are also proposed.
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.
2D/0D Pd@Rh hierarchical heterostructures have been prepared via the facet‐selective epitaxial growth of two parallel triangular Rh nanoplates on two opposite (002)h facets of unconventional 2H‐Pd nanoparticles. Such hierarchical heterostructures exhibit excellent performance toward electrochemical hydrogen evolution reaction in acid electrolyte.
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