Heterostructure of ZnO Nanosheets/Zn with a Highly Enhanced Edge Surface for Efficient CO₂ Electrochemical Reduction to CO

Abstract

Electrochemical reduction of CO2 to valuable chemicals or fuels is critical for closing the carbon cycle and preventing further deterioration of the environment. Here, we discover that by adopting the Zn foil as the substrate, a ZnO two-dimensional sheet array is in situ synthesized on the Zn foil by a facile hydrothermal method. The obtained ZnO sheet array/Zn foil exhibited an outstanding CO2 reduction performance to CO, which showed the highest Faraday efficiency of 85% for CO at −2.0 V (vs Ag/AgCl) with a current density of 11.5 mA/cm2 compared with the freestanding ZnO sheets and particles and excellent stability in the 0.1 M KHCO3 electrolyte. The in situ vertical ZnO sheet array exposed with abundant exposed (11̅00) edge facets can accelerate the electron transfer and improve the number of active sites, which leads to the enhanced reduction performance. Alongside, the density functional theory simulation indicated that the vertical-grown ZnO sheet array possesses lower Gibbs free energy for the CO2 activation, with a more exposed (11̅00) edge surface of ZnO.

Stability of single-atom catalysts for electrocatalysis

“…3 Different from the ORR, OER, and HER, it usually occurs under neutral conditions (such as CO 2 saturated 0.1 M KHCO 3 ; pH is about 6.8) with a relatively more negative potential. 114 Actually, single-atom metals are not in the 0 valent state due to the coordinated binding with ligands, and thus they are likely reduced to a metallic state at a negative potential. 115 Recently, SACs have shown remarkable specific activity and selectivity for the CO 2 RR.…”

Energy conversion efficiency comparison of different aqueous and semi-aqueous CO2 electroreduction systems

“…To calculate the energy conversion efficiency for CO 2 electroreduction, we examined the literature using the CAS SciFinder software and calculated the efficiencies in 107 typical aqueous and semi-aqueous systems. 13–73 We selected the literature reports with a relatively high frequency of citations over the last 30 years. The pH of each CO 2 -saturated solution required for the calculation in this work was measured using an F-53 pH meter (HORIBA, Ltd).…”

Engineering the Interfacial Microenvironment via Surface Hydroxylation to Realize the Global Optimization of Electrochemical CO2 Reduction

“…Zinc oxide (ZnO), characterized by its huge reserves and for being cost-friendly, has been widely investigated for generating CO with moderate selectivity. − The oxidation state of Zn in ZnO as a clear active site provides infinite possibilities to enhance the eCO 2 RR efficiency. − For example, an increased number of active sites could be induced by modulating the ZnO morphology to expose abundant edge facets; the ratio of H 2 /CO obtained on ZnO electrocatalysts could be tuned through controlling the defects and facets . However, almost no attention has been paid to the interfacial microenvironment between ZnO catalysts and CO 2 , a key factor to affect its adsorption and activation.…”