Electrocatalytic CO2 Reduction to Ethylene over CeO2-Supported Cu Nanoparticles: Effect of Exposed Facets of CeO2

Abstract

Fossil fuels are expected to be the major source of energy for the next few decades. However, combustion of nonrenewable resources leads to the release of large quantities of COO2, the primary greenhouse gas. Notably, the concentration of CO2 in the atmosphere is increasing annually at an astounding rate. Electrochemical CO2 reduction (ECR) to value-added fuels and chemicals using electricity from intermittent renewable energy sources is a carbon-neutral method to alleviate anthropogenic CO2 emissions. Despite the steady progress in the selective generation of C1 products (CO and formic acid), the production of multi-carbon species still suffers from low selectivity and efficiency. As an ECR product, ethylene (C2H4) has a higher energy density than do C1 species and is an important industrial feedstock in high demand. However, the conversion of CO2 to C2H4 is plagued by low productivity and large overpotential, in addition to the severe competing hydrogen evolution reaction (HER) during the ECR. To address these issues, the design and development of advanced electrocatalysts are critical. Here, we demonstrate fine-tuning of ECR to C2H4 by taking advantage of the prominent interaction of Cu with shape-controlled CeO2 nanocrystals, that is, cubes, rods, and octahedra predominantly covered with (100), (110), and (111) surfaces, respectively. We found that the selectivity and activity of the ECR depended strongly on the exposed crystal facets of CeO2. The overall ECR Faradaic efficiency (FE) over Cu/CeO2(110) (FE ≈ 56.7%) surpassed that of both Cu/CeO2(100) (FE ≈ 51.5%) and Cu/CeO2(111) (FE ≈ 48.4%) in 0.1 mol·L−1 KHCO3 solutions with an H-type cell. This was in stark contrast to the exclusive occurrence of the HER over pure carbon paper, CeO2(100), CeO2(110), and CeO2(111). In particular, the FE toward C2H4 formation and the partial current density increased in the sequence Cu/CeO2(111)