Nano-ZnO is a potential catalyst material for carbon dioxide electrocatalytic reduction (CO₂RR), but its effective Faraday efficiency (FE) is still below 90% and the current density is less than 300 mA cm^-2, which is not enough to meet industrial requirements.

A new study published in Chem Catalysis and conducted by Prof. WU Zhonghua and Dr. XING Xueqing from the Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences (CAS) and Prof. HAN Buxing from the Institute of Chemistry of CAS synthesized a kind of ZnO nanorods for electrocatalytic CO₂RR. After 500 °C heat-treatment, these ZnO nanorods (500-ZnO) obtained the highest oxygen vacancy content and achieved the highest FE_CO of 98.3%, and a partial current density of 786.56 mA cm^-2 in a 3 M KCl electrolyte.

In this study, a series of advanced detection techniques, such as synchrotron radiation X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and electron paramagnetic resonance, were used to confirm the presence of oxygen vacancies. Density functional theory calculations showed that oxygen vacancies can not only change the d-band of ZnO, but also enhance the activity of CO₂.

Combined with other electrochemical characterization methods, the effect of oxygen vacancy on carbon dioxide electroreduction reaction was discussed. The results showed that oxygen vacancies provided excellent kinetic conditions for CO generation and played a key role in accelerating CO₂ activation and reducing the energy barrier of CO generation.

These findings imply a breakthrough in catalyst materials for the electrocatalytic CO₂RR and highlight the great potential of low-cost ZnO nanorods rich in oxygen vacancies as robust and efficient catalysts for CO₂RR. Their excellent electrocatalytic capabilities in CO₂to CO conversion are expected to promote the cost-effective industrial production and facilitate advances in sustainable energy conversion technologies.

Figure 1. (a) The current density and FE_COover 500-ZnO compared with other catalysts. (b) Plots of FE_CO versus Current density of the 500-ZnO. (c) ATR-SEIRAS spectra of the 500-ZnO at different potentials. (d, e) Zn K-edge XANES spectra and Zn K-edge FT-EXAFS spectra of ZnO nanorods. (f) O 1s XPS spectra. (g) EPR spectra of ZnO nanorods. (h) Gibbs free energy diagrams for CO₂ reduction to CO over ZnO nanorods with/without oxygen vacancy. (Credit: Chem Catalysis)

Figure 2. Carbon dioxide electroreduction map on oxygen-rich vacancies, zinc oxide nanorods. (Credit:Chem Catalysis)

Paper link: https://www.sciencedirect.com/science/article/abs/pii/S2667109324004019?dgcid=author