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

Abstract

The detailed reaction mechanism of electrochemical H 2 O splitting for the oxygen evolution reaction (OER) and the electrochemical ozone production (EOP) still remains unclear over the β−PbO 2 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 PbO 2 (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 (O latt ) and one oxygen atom from H 2 O, 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 PbO 2 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 O 2 /O 3 , which also verified the facile LOM reaction mechanism. DFT calculations reveal that the formation of O vac1 /O vac2 triggered further reactions of H 2 O adsorption and splitting, which refilled the oxygen vacancy and ensured considerable stability of the PbO 2 catalyst. Multiple H 2 O dissociation pathways were proposed on PbO 2 (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.

Unraveling the Role of F in Electrochemical Ozone Generation on the F-Doped PbO2 Electrode

“…Trasatti also reported the lowest formation enthalpy of PbO 2 (−48.1 kJ/mol −1 O atoms) among a series of metal oxides in lower to higher oxide transition reaction. 49 In addition, concerning the unique covalent interaction of Pb−O on PbO 2 than most transition-metal oxides (such as IrO 2 , a benchmark oxygen evolution catalyst), 31 we suggested that the surface lattice oxygen of PbO 2 is less constrained by the crystal lattice than IrO 2 and thus is easy to detach from the PbO 2 crystal facet under harsh conditions. Our isotope labeled O 2 experiment provided the conclusive evidence that oxygen can take part in the O 3 generation during the water oxidation process.…”

“…Because our PbO 2 and electrolyte were unlabeled by 18 O, if the 18 O 2 was inert component during the electrolysis process, only the 48 O 3 would be generated. In other words, the 50 27,31 They found that oxygen vacancy formation was exothermic on PbO 2 surfaces, which means that the lattice oxygen is easy to consume and refill and dominates the O 3 generation via the LOM. 31 This is consistent with experimental evidence.…”

“…In other words, the 50 27,31 They found that oxygen vacancy formation was exothermic on PbO 2 surfaces, which means that the lattice oxygen is easy to consume and refill and dominates the O 3 generation via the LOM. 31 This is consistent with experimental evidence. For example, to the best of our knowledge, the initial thermal decomposition of rutile PbO 2 is as low as 200 °C, while that of rutile IrO 2 is as high as 1100 °C.…”

“…Recently, accompanying the extensive and intensive investigations on the oxygen evolution reaction (OER), especially the findings of the lattice oxygen mechanism (LOM), − the formation mechanism of special byproduct (O 3 ) during the water oxidation process has aroused many researchers’ interest again. ,− By density functional theory (DFT) calculations, Gibson et al reported that the coupling step in eq is an Eley–Rideal style reaction mechanism on β-PbO 2 in which the surface O 2 generated first desorbs and then attacks the surface bridging oxygen on the (110) plane of β-PbO 2 to form O 3 . , Later, Jiang et al proved that the EOP process on β-PbO 2 follows the LOM process . Further DFT calculations reveal that the surface lattice oxygen atoms on the β-PbO 2 (110) or (101) plane are highly active and can easily migrate, thus contributing to the formation of O 2 /O 3 . The role of H 2 O and lattice oxygen during EOP for PbO 2 is proved by Jianguo et al , However, there is still a lack of studies on identifying the role of dioxygen (O 2 ) in electrochemical ozone formation.…”

“…Further DFT calculations reveal that the surface lattice oxygen atoms on the β-PbO 2 (110) or (101) plane are highly active and can easily migrate, thus contributing to the formation of O 2 /O 3 . The role of H 2 O and lattice oxygen during EOP for PbO 2 is proved by Jianguo et al , However, there is still a lack of studies on identifying the role of dioxygen (O 2 ) in electrochemical ozone formation. Recently, Rodríguez-Peña et al found a phenomenon that increasing the oxygen pressure in the commercial PEM electrolyzer equipped with boron-doped diamond lattice electrodes from 1 to 2 bar can improve the production of ozone significantly, while replacing it with nitrogen will decrease the production of ozone. , This indicates that oxygen may behave as a raw reactant in the generation of O 3 .…”