Unconventional-Phase Crystalline Materials Constructed from Multiscale Building Blocks

Abstract

Crystal phase, an intrinsic characteristic of crystalline materials, is one of the key parameters to determine their physicochemical properties. Recently, great progress has been made in the synthesis of nanomaterials with unconventional phases that are different from their thermodynamically stable bulk counterparts via various synthetic methods. A nanocrystalline material can also be viewed as an assembly of atoms with long-range order. When larger entities, such as nanoclusters, nanoparticles, and microparticles, are used as building blocks, supercrystalline materials with rich phases are obtained, some of which even have no analogues in the atomic and molecular crystals. The unconventional phases of nanocrystalline and supercrystalline materials endow them with distinctive properties as compared to their conventional counterparts. This Review highlights the state-of-the-art progress of nanocrystalline and supercrystalline materials with unconventional phases constructed from multiscale building blocks, including atoms, nanoclusters, spherical and anisotropic nanoparticles, and microparticles. Emerging strategies for engineering their crystal phases are introduced, with highlights on the governing parameters that are essential for the formation of unconventional phases. Phase-dependent properties and applications of nanocrystalline and supercrystalline materials are summarized. Finally, major challenges and opportunities in future research directions are proposed.

Seeded Synthesis of Unconventional 2H-Phase Pd Alloy Nanomaterials for Highly Efficient Oxygen Reduction

“…Recently, thanks to the great progress on the phase engineering of nanomaterials (PEN), − it has been revealed that tuning the crystal phase of noble metal nanomaterials can efficiently tune their functions and properties due to the different electronic structures arising from the distinct atomic arrangements. , Importantly, noble-metal-based nanomaterials with unconventional crystal phases, which are different from the thermodynamically stable phases in bulk materials, exhibit superior performance compared with their conventional counterparts in various catalytic reactions including electrochemical hydrogen evolution, , nitrogen reduction, carbon dioxide (CO 2 ) reduction, and alcohol oxidation . However, the preparation of noble-metal-based alloy nanomaterials with unconventional crystal phases and tunable compositions still remains a great challenge due to their thermodynamically unstable nature.…”

Wet-chemical synthesis of two-dimensional metal nanomaterials for electrocatalysis

“…The Au seeds eventually assembled into ultrathin 2D square-like nanosheets with a thickness of ∼2.4 nm. Impressively, this is the first time Au nanosheets have been directly prepared with pure 2H phase through a wet-chemical route [ 74 , 75 ]. It is worth mentioning that the Au square-like nanoplates with an alternating 2H and fcc crystal phase could be obtained using the aforementioned 2H Au nanosheets as templates via secondary growth of Au [ 76 ].…”

Rational Design of Superior Electrocatalysts for Water Oxidation: Crystalline or Amorphous Structure?

“…The molecular structure with long‐range ordering feature is defined as crystalline structure (Figure 1a). Many efficient strategies can be applied to moderate the physicochemical properties of crystalline structures, such as phase engineering (including some special phases), [ 27–29 ] defect chemistry, [ 30,31 ] corrosion engineering, [ 32,33 ] strain engineering, [ 34,35 ] and many other methodologies. [ 8,36 ] Generally, initial crystalline materials could maintain crystallinity or become partially amorphous during/after the OER (Figure 1d,e and Table 1), which is determined by the initial physicochemical properties of the crystalline materials.…”