Engineering high-energy surfaces of noble metal nanocrystals with enhanced catalytic performances

Tailoring of the surface structure of noble metal nanocrystals is a hot research topic because of the fascinating surface structure-dependent properties in enormous applications, such as heterogeneous catalysis. Due to high densities of atomic steps and kinks and their abundance of unsaturated coordination sites, noble metal NCs with high-energy surfaces often exhibit superior performances compared to those with low-energy surface structures. A complete understanding of the growth mechanisms of noble-metal NCs with high-energy surface structures would enable the rational design of noble metal NCs with optimized performances for specific applications. In this review, we concentrate on the growth mechanisms of noble-metal NCs with high-energy facets by summarizing the state-of-the-art progress in the surface structure-controlled synthesis of noble metal NCs with high-energy facets. By carefully considering both the thermodynamic and kinetic factors that affect the surface structures, we intentionally classify different approaches into four categories (i.e., surface-regulating-agent assisted strategies, supersaturation controlled strategies, electrochemical methods, and template directed methods), and insights into the respective growth mechanisms are demonstrated by representative examples. Especially, we highlight the role of supersaturation in the formation of the high-energy surface, which successfully explained apparent contradictory results when only taking the capping effect into consideration. Then several typical examples are given to demonstrate the versatility of the high-energy facets in improving both catalytic activity and selectivity. In addition, the stability of high-energy facets is also discussed. Finally, the remaining challenges and perspectives for future directions are given for this promising field of research. We hope the deep and comprehensive understanding the growth mechanism of the,nanocrystals would help to guild the rational design of functional nanomaterials with desired outstanding properties. (C) 2016 Elsevier Ltd. All rights reserved.