Noble metal nanocrystals (NCs) are often densely packed in their most stable forms that are determined by a combination of effects arising from the electronic, magnetic, geometric, and phononic properties of the NCs. These packing modes usually include the densest packed polytypes of Barlow packings and more open or distorted packings with slightly lower atomic packing factors. The structural modulation strategies of NCs towards the better performances for diverse applications are usually limited to the crystal size, shape, and surface control, which have been robustly studied and documented. An exciting emerging field related to structural engineering of noble metal NCs turns out to be the crystal phase control, which allows the chemical synthesis of energetically high-lying phases of NCs and leads to intriguing performances in catalysis and energy conversion. This article provides a comprehensive review of crystal phase regulation that endows both noble metal and noble-metal-based alloy NCs with unique electronic structures and enhanced performances. The basic principles, general design rationale, synthetic approaches, and structural characterizations for a variety of successful case studies related to crystal phase engineering are reviewed and discussed. In the end, the perspectives and challenges associated with the development of a more controllable chemical synthetic strategy towards the high-energy phases of noble metal NCs are put forward.

Proton exchange membrane fuel cells have been considered as promising energy conversion device. Alloying 3d transition metals with noble metals not only highly improve the performanc of noble metals-based catalysts...

The decoration of noble metal catalysts with specific main group or transition metal atoms offers an effective way to improve the catalytic performance through electronic structure regulation and active site optimization without losing the active surface area. Herein, icosahedral Pd nanocrystals catalysts with highly dispersed Bi atoms decoration have been realized by a simple photochemical reduction approach. The decoration of Bi atoms maintains the original Pd cyclic penta‐twinned structure. The deposition amount of Bi atoms, which greatly affect the catalytic performance, is fundamentally regulated by the irradiation time. Compared with pure Pd, the Pd−Bi icosahedral nanocrystals show significant improvement in electrocatalytic activity towards formic acid oxidation. Besides, the catalytic performance is correlated with the content of Bi. The optimal performance is occurred at the Bi content of 2.86%.