The fate of nanoparticle surface chemistry during reductive electrosynthesis in aprotic media

Reductive electrochemical coupling of carbon dioxide with organic molecules (electrocarboxylation, EC) represents a green route towards value-added carboxylic acids and serves as a promising strategy for carbon footprint mitigation. Despite the industrial prospects of this synthetic process, little has been done towards the optimization of cathode materials at the nanoscale. Herein, we pave the way towards the use of metal nanoparticles (NPs) as electrocatalysts in EC by demonstrating the effects of NP surface chemistry on electroorganic transformations and the evolution of surface functionalization in the course of reductive electrosynthesis in aprotic media. Using spherical Au NPs capped with citrate or cetylpyridinium chloride (CPC) as our study subjects, we examined the effect of Au NP surface chemistry on the selectivity of EC of benzyl bromide in acetonitrile and determined the fate of the surface adsorbates of Au NPs in the course of the reaction using Raman spectroscopy and X-ray photoelectron spectroscopy. We show that the CPC-stabilized Au NPs outperform the citrate-stabilized NPs at a low applied potential of -1.5 V vs. Ag/Ag⁺ with the former showing an almost two-fold increase in the faradaic efficiency towards phenylacetic acid. This higher selectivity is attributed to the reaction on the liberated Au surface stemming from the stripping of CPC molecules. In contrast to the CPC-functionalized NPs, the citrate-stabilized Au NPs retain their adsorbates during the reaction, which undergo electrochemical transformations during EC.