Noble metal nanocrystals have been extensively utilized as promising catalysts for chemical transformations and energy conversion. One of their significant applications lies in electrode materials in fuel cells (FCs) due to their superior electrocatalytic performance towards the reactions both on anode and cathode. Nowadays, tremendous efforts have been devoted to improve the catalytic performance and minimize the usage of precious metals. Constructing multicomponent noble metal nanocrystals with complex structures provides the opportunity to reach this goal due to their highly tunable compositions and morphologies, leading to the modification of the related electrochemical properties. In this review, we first highlight the recent advances in the controllable synthesis of noble metal alloy complex nanostructures including nanoframes/nanocages, branched structures, concave/convex structures, core-shell structures and ultrathin structures. Then the effects of the well-defined nanocrystals on the modified and improved electrochemical properties are outlined. Finally, we make a conclusion with the points on the challenges and perspectives of the controllable synthesis of noble metal alloy complex nanostructures and their electrocatalytic performance.

Metal-organic frameworks (MOFs) are potentially useful molecular materials that can exhibit structure flexibilities induced by some external stimuli. Such structure transformations can furnish MOFs with improved properties. The shape-controlled growth of MOFs combined with crystal-structure transformation is rarely achieved. Herein, we demonstrate the synthesis of hierarchical Zn/Ni-MOF-2 nanosheet-assembled hollow nanocubes (NAHNs) by a facile surfactant-free solvothermal approach. The unique nanostructures undergo crystal-structure transformation from Zn/Ni-MOF-5 nanocubes to Zn/Ni-MOF-2 nanosheets, which is analogous to the dissolution and recrystallization of inorganic nanocrystals. The present synthetic strategy to fabricate isostructural MOFs with hierarchical, hollow, and bimetallic nanostructures is expected to expand the diversity and range of potential applications of MOFs.

To enhance the intrinsic properties and realize novel functionalities toward desired applications, it is of great significance to construct molybdenum carbide with unique architecture but still remains highly challenging. Herein, we demonstrate a simple synthetic method. Initially, Mo-based polyoxometalate-anion-incorporated Ni-MOF (metal–organic framework) hollow structure is prepared through dissolution–regrowth process. Then, carbon-containing polymer is coated on the surface of the hollow precursor. After being annealed at high temperature, carbon-layer-coated Ni-decorated hollow molybdenum carbide structures are obtained successfully. Due to the unique composition and configuration, these hollow structures exhibit remarkable hydrogen evolution reaction properties and stabilities.

Octahedral Pt-Cu nanoframes have been synthesized by a one-pot aqueous method. Due to the unique structure and possible synergetic effect of Pt and Cu components, these octahedral Pt-Cu nanoframes exhibited significantly enhanced catalytic activity toward the electro-oxidation of formic acid in comparison with commercial Pt black and Pt/C catalysts.

Uniform Pt-Cu alloy nanocrystals in the shape of dendrite, yolk-cage, and box structures are prepared via a facile wet-chemical reduction route in which glycine is demonstrated to alter the reduction kinetics of metal cations, critical to the morphology of the obtained product. These alloy nanocrystals exhibit superior specific activity and stability in the electro-oxidation of methanol.