Elucidating facet dependent electronic and electrochemical properties of Cu2O nanocrystals using AFM/SCEM and DFT

Cuprous oxide (Cu2O) has extensively been studied owing to its excellent optical, magnetic, and catalytic properties. Many of these properties are facet-dependent and have not been well elucidated. This work synthesized cubic, cuboctahedral, octahedral, and rhombic dodecahedral shaped Cu2O nanocrystals of ∼300 nm in size to evaluate the facet-dependent electrochemical activities. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were firstly used to reveal the average electrochemical activities at the ensemble level. Atomic force microscopy-scanning electrochemical microscopy (AFM-SECM) was further used to assess the electrochemical activities of different Cu2O nanocrystals at the facet level. Hexaammineruthenium (III) chloride ({Ru(NH3)6}Cl3) was employed as the probe molecules that reacted with four different Cu2O nanocrystals under 400 mV and yielded ∼300 pA current between the probing tip and the nanocrystal surface. The tip-current mapping results indicate that rhombic dodecahedral Cu2O exhibits higher electrocatalytic activity than other shaped Cu2O, due to the presence of dominant exposed facet of {110} as indicated by the relatively high tip current. Density-functional theory (DFT) calculations confirmed the facet dependence of local surface energy and electronic structure of Cu2O nanocrystals. Besides electrochemical activity, the surface work function and adsorptive properties were both observed to vary with the shape and dominant exposed facets of Cu2O. This study presented a unique experimental and computational chemistry approach to analyze surface electrochemical properties of Cu2O crystals at a crystalline facet level.