Insights into electrochemically anodic H₂O₂ synthesis on titanium dioxide in carbonate-based electrolytes

For electrochemically anodic H₂O₂ synthesis, which one of bicarbonate (HCO₃⁻) and carbonate (CO₃²⁻) species plays a more important surface-mediating role in the formation of H₂O₂ is still in debate. In this study, titanium dioxide (TiO₂) was utilized as a representative anode to evaluate the performance tendencies for H₂O₂ production in electrolytes with varying pH levels at different potentials. The findings support the mechanism that the formation of H₂O₂ is more favorable when HCO₃⁻ predominates in the vicinity of the anode. When considering the effects of both electro-decomposition and self-decomposition of H₂O₂, the findings are consistent. Interestingly, under the conditions more conducive to the H₂O₂ generation, the electro-decomposition of H₂O₂ likely could be more effectively inhibited. The adsorption of HCO₃⁻ and CO₃²⁻ species on TiO₂ are explored by performing an attenuated total reflection Fourier transform infrared spectroscopy. The ratio of the absorption peak area for HCO₃⁻ to CO₃²⁻ species on TiO₂, following an anodic reaction in carbonate-based electrolytes at varying pH levels, generally escalates with the heightened application of potentials. These results likely suggest that a local acidification took place near the anode, thereby further substantiating the pivotal impact of the equilibrium shift between carbonate species in the generation of H₂O₂.