Synthesis and Electrocatalytic HER Studies of Carbene-Ligated CuP Nanocrystals.

N-heterocyclic carbenes (NHCs) are an important class of ligands capable of making strong carbon-metal bonds. Recently, there has been a growing interest in the study of carbene-ligated nanocrystals, primarily coinage metal nanocrystals, which have found application as catalysts for numerous reactions. The general ability of NHC ligands to positively affect the catalytic properties of other types of nanocrystal catalysts remains unknown. Herein, we present the first carbene-stabilized CuP nanocrystals. Inquiries into the mechanism of formation of NHC-ligated CuP nanocrystals suggest that crystalline CuP forms directly as a result of a high-temperature metathesis reaction between a tris(trimethylsilyl)phosphine precursor and an NHC-CuBr precursor, the latter of which behaves as a source of both the carbene ligand and Cu. To study the effect of the NHC surface ligands on the catalytic performance, we tested the electrocatalytic hydrogen evolving ability of the NHC-ligated CuP nanocrystals and found that they possess superior activity to analogous oleylamine-ligated CuP nanocrystals. Density functional theory calculations suggest that the NHC ligands minimize unfavorable electrostatic interactions between the copper phosphide surface and H during the first step of the hydrogen evolution reaction, which contributes to the superior performance of NHC-ligated CuP catalysts as compared to oleylamine-ligated CuP catalysts.