Particle Size Effects in the Catalytic Electroreduction of CO₂ on Cu Nanoparticles

TLDR

This study investigates how particle size influences catalytic CO₂ electroreduction on size‑controlled Cu nanoparticles. Cu nanoparticles (2–15 nm) were synthesized, their CO₂ electroreduction activity and selectivity measured against bulk Cu, and size‑dependent surface coordination was modeled to rationalize the results, enabling DFT verification for the smallest (~2 nm) particles. Smaller Cu nanoparticles (<5 nm) exhibit markedly higher H₂ and CO production with reduced hydrocarbon selectivity, due to increased low‑coordinated surface sites, offering new activity‑selectivity‑size relationships for CO₂ electroreduction.

Abstract

A study of particle size effects during the catalytic CO2 electroreduction on size-controlled Cu nanoparticles (NPs) is presented. Cu NP catalysts in the 2-15 nm mean size range were prepared, and their catalytic activity and selectivity during CO2 electroreduction were analyzed and compared to a bulk Cu electrode. A dramatic increase in the catalytic activity and selectivity for H2 and CO was observed with decreasing Cu particle size, in particular, for NPs below 5 nm. Hydrocarbon (methane and ethylene) selectivity was increasingly suppressed for nanoscale Cu surfaces. The size dependence of the surface atomic coordination of model spherical Cu particles was used to rationalize the experimental results. Changes in the population of low-coordinated surface sites and their stronger chemisorption were linked to surging H2 and CO selectivities, higher catalytic activity, and smaller hydrocarbon selectivity. The presented activity-selectivity-size relations provide novel insights in the CO2 electroreduction reaction on nanoscale surfaces. Our smallest nanoparticles (~2 nm) enter the ab initio computationally accessible size regime, and therefore, the results obtained lend themselves well to density functional theory (DFT) evaluation and reaction mechanism verification.