Selectivity on Etching: Creation of High-Energy Facets on Copper Nanocrystals for CO2 Electrochemical Reduction.

Creating high-energy facets on the surface of catalyst nanocrystals represents a promising method for enhancing their catalytic activity. Herein we show that crystal etching as the reverse process of crystal growth can directly endow nanocrystal surfaces with high-energy facets. The key is to avoid significant modification of the surface energies of the nanocrystal facets by capping effects from solvents, ions, and ligands. Using Cu nanocubes as the starting material, we have successfully demonstrated the creation of high-energy facets in metal nanocrystals by controlled chemical etching. The etched Cu nanocrystals with enriched high-energy {110} facets showed significantly enhanced activity toward CO2 reduction. We believe the etching-based strategy could be extended to the synthesis of nanocrystals of many other catalysts with more active high-energy facets.