Lattice Oxygen of PbO2 (101) Consuming and Refilling via Electrochemical Ozone Production and H2O Dissociation

The detailed reaction mechanism of electrochemical H2O splitting for the oxygen evolution reaction (OER) and the electrochemical ozone production (EOP) still remains unclear over the β–PbO2 catalysts due to the underlying competitive reaction pathways including the adsorbate evolution mechanism (AEM) as well as the lattice oxygen mechanism (LOM). Periodic density functional theory (DFT) calculations were applied in this work to give a comprehensive understanding of the OER/EOP mechanism on the PbO2 (101) surface. The reaction networks including the AEM, LOM-1, and LOM-2 were established, and the results show that the LOM-2 reaction pathway exhibited the highest reactivity, which involves two surface lattice oxygens (Olatt) and one oxygen atom from H2O, with the theoretical overpotential calculated to be 0.48 V. Different potential-determining steps (PDSs) were predicted depending on the above three reaction pathways. Surprisingly, DFT calculations also found that the oxygen vacancy formation was exothermic on PbO2 surfaces, which was significantly different from most transition-metal oxides. Negative oxygen vacancy formation energies indicated that the surface lattice oxygens could easily migrate and couple to form O2/O3, which also verified the facile LOM reaction mechanism. DFT calculations reveal that the formation of Ovac1/Ovac2 triggered further reactions of H2O adsorption and splitting, which refilled the oxygen vacancy and ensured considerable stability of the PbO2 catalyst. Multiple H2O dissociation pathways were proposed on PbO2 (101) with oxygen vacancy sites: the acid–base interaction mechanism and the vacancy-fulfilling mechanism. This work gives a comprehensive understanding of reaction mechanisms for OER and EOP processes.