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 (OV) 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), OV can still be generated easily on PbO2 surfaces. Our subsequent kinetic and thermodynamic analyses show that these OV 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 OV 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.