Origin of the Activity of Electrochemical Ozone Production Over Rutile PbO₂ Surfaces

Ozonation water treatment technology has attracted increasing attention due to its environmental benign and high efficiency. Rutile PbO₂ is a promising anode material for electrochemical ozone production (EOP). However, the reaction mechanism underlying ozone production catalyzed by PbO₂ was rarely studied and not well-understood, which was in part due to the overlook of the electrochemistry-driven formation of oxygen vacancy (O_V) of PbO₂. Herein, we unrevealed the origin of the EOP activity of PbO₂ starting from the electrochemical surface state analysis using density functional theory (DFT) calculations, activity analysis, and catalytic volcano modeling. Interestingly, we found that under experimental EOP potential (i. e., a potential around 2.2 V vs. reversible hydrogen electrode), O_V can still be generated easily on PbO₂ surfaces. Our subsequent kinetic and thermodynamic analyses show that these O_V sites on PbO₂ surfaces are highly active for the EOP reaction through an interesting atomic oxygen (O*)-O₂ coupled mechanism. In particular, rutile PbO₂(101) with the "in-situ" generated O_V exhibited superior EOP activities, outperforming the (111) and (110) surfaces. Finally, by catalytic volcano modeling, we found that PbO₂ is close to the theoretical optimum of the reaction, suggesting a superior EOP performance of rutile PbO₂. All these analyses are in good agreement with previous experimental observations in terms of EOP overpotentials. This study provides the first volcano model to explain why rutile PbO₂ is among the best metal oxide materials for EOP and provides new design guidelines for this rarely studied but industrially promising reaction.