Precise control over the size, shape, composition, structure, and crystal phase of random alloy and intermetallic nanocrystals has been intensively explored in technologically important applications in recent years. Different from the monometallic nanocrystals and other types of structural nanocrystals such as core−shell and heterostructured nanocrystals, well-defined multimetallic random alloy and intermetallic nanocrystals exhibit unique and intriguing physicochemical properties, serving as ideal models for benefiting the structure-to-property studies. As such, random alloy and intermetallic nanocrystals have attracted extensive attention and interest in scientific research and shown huge potential in various fields. In this review, we focus specifically on summarizing the synthetic principles and strategies developed to form random alloy and intermetallic nanocrystals with enhanced performance. Some representative examples are purposely selected for emphasizing basic concepts and mechanistic understanding. We then highlight the fascinating properties and widespread applications of random alloy and intermetallic nanocrystals in electrocatalysis, heterogeneous catalysis, optical and photocatalysis, as well as magnetism and conclude the review by addressing the prospects and current challenges for the controlled synthesis of random alloy and intermetallic nanocrystals.

Ni–Co sulfide nanowires synthesized by a two-step hydrothermal method show good performance when used as the positive electrode for asymmetric supercapacitors.

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We report a quantitative understanding of the reduction kinetics responsible for the formation of Pd-Pt bimetallic nanocrystals with two distinctive structures. The syntheses involve the use of KBr to manipulate the reaction kinetics by influencing the redox potentials of metal precursor ions via ligand exchange. In the absence of KBr, the ratio between the initial reduction rates of PdCl4(2-) and PtCl4(2-) was about 10.0, leading to the formation of Pd@Pt octahedra with a core-shell structure. In the presence of 63 mM KBr, the products became Pd-Pt alloy nanocrystals. In this case, the ratio between the initial reduction rates of the two precursors dropped to 2.4 because of ligand exchange and, thus, the formation of PdBr4(2-) and PtBr4(2-). The alloy nanocrystals took a cubic shape owing to the selective capping effect of Br(-) ions toward the {100} facets. Relative to the alloy nanocubes, the Pd@Pt core-shell octahedra showed substantial enhancement in both catalytic activity and durability toward the oxygen reduction reaction (ORR). Specifically, the specific (1.51 mA cm(-2)) and mass (1.05 A mg(-1) Pt) activities of the core-shell octahedra were enhanced by about four- and three-fold relative to the alloy nanocubes (0.39 mA cm(-2) and 0.34 A mg(-1) Pt, respectively). Even after 20000 cycles of accelerated durability test, the core-shell octahedra still exhibited a mass activity of 0.68 A mg(-1) Pt, twice that of a pristine commercial Pt/C catalyst.

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., facecentered 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 (CO 2 RR) 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 CO 2 RR catalysts in H-type electrochemical cells.

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Three-dimensional (3D) interconnected metal alloy nanostructures possess superior catalytic performance owing to their advantageous characteristics, including improved catalytic activity, corrosion resistance, and stability. Hierarchically structured Ni-Cu alloys composed of 3D network-like microscopic branches with nanoscopic dendritic feelers on each branch were crafted by a facile and efficient hydrogen evolution-assisted electrodeposition approach. They were subsequently exploited for methanol electrooxidation in alkaline media. Among three hierarchically structured Ni-Cu alloys with different Ni/Cu ratios (Ni Cu , Ni Cu , and Ni Cu ), the Ni Cu electrode exhibited the fastest electrochemical response and highest electrocatalytic activity toward methanol oxidation. The markedly enhanced performance of Ni Cu eletrocatalyst can be attributed to its alloyed structure with the proper Ni/Cu ratio and a large number of active sites on the surface of hierarchical structures.

Ni-based bimetallic alloys have superior physiochemical characteristics compared to monometallic Ni. In this study, a new type of low cost bimetallic NimCon (n + m = 4) electrocatalysts with high active surface were synthesized on Ti substrate through a hydrogen evolution assisted electrodeposition method. The as-prepared NimCon were characterized by XRD, EDS, and SEM. It was revealed that the composition, surface morphology, as well as the crystal phase structure of the bimetallic NimCon electrocatalysts were significantly changed with the increased content of cobalt. Electrochemical measurements showed that the bimetallic NimCon catalysts, compared with the monometallic Ni, have superior catalytic activity and stability toward the methanol electrooxidation reaction. Additionally, Ni2Co2 sample presented the highest oxidation current density and the best durability. The mechanism study based on electrochemical experiments and density functional theory based calculations showed that the doping of Co in NimCon can signally improve the surface coverage of the redox species, weaken the CO adsorption, as well as adjust the CH3OH adsorption. Such understanding is of important directive significance to design efficient nonprecious catalysts.