Revealing the roles of oxygen vacancies in NiO-CeO2 redox catalysts for electrocatalytic ozonation: Mechanistic study via in situ Raman spectroscopy

Abstract

Improving the O-3 activation via electrocatalysis is a promising approach to achieve higher hydroxyl radical (OH) production, however, the mechanisms and performance of electrocatalytic ozonation (ECO) remains unclear. Herein, we investigated the redox enhancement effect via preparing the asymmetric oxygen vacancies (O-V) contained NiO-CeO2 and doped on carbon felt electrode to enhance anodic O-3 activation for atrazine (ATZ) demineralization. XPS and ESR liquid analysis results revealed that O-V content in NiO-CeO2 electrode are crucial sites for O-3 decomposition and facilitating the OH generation. In situ Raman spectroscopy finding evidenced the intermetallic redox behaviour between NiO and CeO2 in ECO. As a result, ECO using NiO-CeO2 exhibited 3.4-times higher ATZ demineralization rate and 84.4% lower energy consumption (149 kWh/mg) than sole ozonation (960 kWh/mg). In addition, NiO-CeO2 electrode in ECO also showed excellent demineralization performance toward SMX and BPA. Meanwhile, the leaching of Ce(III) and Ni(II) from NiO-CeO2 were not detected in ECO. The toxicities of ATZ degradation by-products were reduced, as proved by QSAR predictions and seed germination. Notably, NiO-CeO2 electrode exhibited excellent reusability performance in consecutive seven cycles ECO tests and outstanding stability in continuous-stirred-tank-reactor experiments, with 84% ATZ demineralization for up to 10 hr. This study provides mechanistic insights into the roles of O-V in redox enhancement to improve OH generation for water treatment.