Insights into the mechanism of electrochemical ozone production via water splitting on the Ni and Sb doped SnO2 catalyst

Abstract

The H₂O splitting mechanism is a very attractive alternative used in electrochemistry for the formation of O₃. The most efficient catalysts employed for this reaction at room temperature are SnO₂-based, in particular the Ni/Sb–SnO₂ catalyst. In order to investigate the H₂O splitting mechanism density functional theory (DFT) was performed on a Ni/Sb–SnO₂ surface with oxygen vacancies. By calculating different SnO₂ facets, the (110) facet was deemed most stable, and further doped with Sb and Ni. On this surface, the H₂O splitting mechanism was modelled paying particular attention to the final two steps, the formation of O₂ and O₃. Previous studies on β-PbO₂ have shown that the final step in the reaction (the formation of O₃) occurs via an Eley–Rideal style interaction where surface O₂ desorbs before attacking surface O to form O₃. It is revealed that for Ni/Sb–SnO₂, although the overall reaction is the same the surface mechanism is different. The formation of O₃ is found to occur through a Langmuir–Hinshelwood mechanism as opposed to the Eley–Rideal mechanism. In addition to this the relevant adsorption energies (E_ads), Gibb’s free energy (ΔG_rxn) and activation barriers (E_act) for the final two steps modelled in the gas phase have been shown, providing the basis for a tool to develop new materials with higher current efficiencies.