Mechanistic Study of Catalase- and Superoxide Dismutation-Mimic Activities of Cobalt Oxide Nanozyme from First-Principles Microkinetic Modeling

Cobalt oxide (Co3O4) has attracted considerable interest because of its high catalytic activity, especially for intrinsic catalase (CAT)-mimic and superoxide dismutation (SOD)-mimic activities. However, understanding of its catalytic mechanism from atomic or molecular level remains limited. Here, we propose base-like dissociative, acid-like dissociative and bi-hydrogen peroxide associative mechanisms of CAT-mimic activity, Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms of SOD-mimic activity on cobalt oxide surface with atomistic thermodynamic and kinetic details by a combination of rigorous density functional theory and microkinetic modeling. The catalytic activity of Co3O4 depends strongly on their size and structure. In this study, Co3O4 nanozyme with different size and structure exhibited different catalytic activities in the order of (Co3O4)(2) > (Co3O4)(3) > Co3O4. This order is closely related to their weak, tunable Co-O bonds. Our microkinetic modeling analysis shows that bi-hydrogen peroxide associative mechanisms (mechanism C) of CAT-mimic activity and ER mechanism of SOD-mimic activity for (Co3O4)(2) are favorable, which is identified by the rate-determining steps (RDS), Energy span model (ESM), and microkinetic modeling analysis. For the CAT-mimic activities on (Co3O4)(n) surface, Campbell's degree of rate control analysis indicates the key to catalyst improvement and design is to stabilize the key steps, which are related to the formation of H2O molecular. For the SOD-mimic activities of (Co3O4)(n), we find the formation of H2O2 molecular to be the sole rate-controlling step. Degree of the thermodynamic rate control analysis reveals that the stronger H2O2*, OH* binding would facilitate the reaction of CAT-like activities of (Co3O4)(n). And the adsorbed OHOO* with large negative degree of thermodynamic rate control would inhibit the reaction of CAT-like activities of (Co3O4)(n). Our results have not only provided new insights into deciphering (Co3O4)(n) artificial enzymes, but will also facilitate the design and construction of other types of target-specific artificial enzymes.