Single crystal with ordered atom arrangement in lattice and amorphous solids, where atom arrangement is long-range disordered, are two end-structures for solid. Metals are usually prepared in the form of polycrystals with amorphous grain boundaries. The controls in phase and crystalline defects are conventional methods to improve metal properties, such as the typical metal-strengthening mechanism of precipitate strengthening and dislocation strengthening. In contrast, metallic glass is known for its amorphous structure and high strength (6 GPa for Co-based metallic glass), but deformation softening and strain localization lead to intrinsic brittleness at room temperature. Here, we proposed the super-nano-dual-phase (SNDP) nanostructured metals as a new family of nanostructural metallic materials with structural units within the size range of 1 ~ 10 nm. The properties and mechanical behaviors of the SNDP materials are totally different from the conventional crystalline material and amorphous solids. Despite the great scientific significance, the development and application of SNDP materials face several challenges: a) A scalable strategy to prepare homogeneous SNDP nanostructured films for a variety of metals (Pt, Pd, Ru, Mg, Al, etc.); b) The interaction mechanism of the supra-nanometer sized dual-phases and the effects on properties; c) The exploitations on the high-value application of the SNDP nanostructured materials.
Super-nano-dual-phase nanostructured materials with high strength and high ductility
The development of SNDP glass-crystal materials depends on sophisticated design of alloy composition that has critical glass forming ability, avoiding the formation of fully amorphous or crystalline structures. The preparation process, including power, temperature and pressure, is controlled strictly to tune the growth of super-nano-sized grains. The SNDP material is expected to comprise a crystalline core with a grain size of less than 10 nm and an amorphous shell which resembles a grain boundary zone of several nanometers. When the SNDP material is under strain, the crystalline phase could block the propagation of shear bands emitted from the amorphous shell, suppressing the strain softening of amorphous phase. Moreover, the amorphous shell might impede the gliding of the grains and the motion of dislocations, preventing the occurrence of reverse Hall-Petch effect. Therefore, the unique synergy effects of SNDP structure could contribute to the ideal strength with high ductility.
Figure 1 The advanced physical vapor deposition instruments at NPMM, introduced for the development of SNDP materials.
Super-nano-dual-phase nanostructuring for efficient noble-metal catalyst
Noble-metal-based electrochemical catalysts with excellent catalytic efficiency and product selectivity are widely utilized in essential energy conversion reactions to convert atmospheric water, carbon dioxide, and nitrogen into high-value energy products (hydrogen, hydrocarbon, and ammonia). However, the large-scale industrial generation of hydrogen, the core of next-generation sustainable energy system, is constrained by the scarcity and expensiveness of platinum group noble-metal-based catalysts and the instability in complex production conditions. SNDP materials with substantial phase interfaces are competitive and promising alternatives to traditional nanomaterial catalysts for hydrogen evolution reaction (HER), possessing commercialization potential and outstanding catalytic performance.
The noble-metal SNDP materials with controllable constituted phases and substantial interfaces provide fertile active sites that primarily enhance the catalytic efficiency. Besides, the SNDP metals composed of crystalline and amorphous phase could avoid the agglomeration problem of typical nanocatalysts. The excellent solution permeability and self-stabilization behavior of the amorphous phase could further improve the electrocatalytic durability. The unique SNDP design offers more modulation degrees on microstructure compared with typical low-dimensional nanocatalysts. We could tailor the concentration of noble metals, nanocrystal orientation and crystal-glass proportion of the SNDP metals to significantly improve the HER activity with ultrahigh catalytic activity, and simultaneously maintain excellent electrochemical stability.
Figure 2 The schematic diagrams of SNDP nanostructures.
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