Anodic H ₂ O ₂ Production via CO ₃ ²⁻ /HCO ₃ ⁻ ‐Mediated Spillover Effect in Three‐Phase Electrochemical System

Two-electron water oxidation reaction (2e^- WOR) mediated by (bi)carbonate (CO₃ ^2-/HCO₃ ^-) is promising for anodic H₂O₂ production. However, previous H₂O₂ yields are usually unsatisfactory due to low local CO₃ ^2-/HCO₃ ^- concentration at the solid/liquid interface. These sluggish reaction rates mainly result from the restricted ion diffusion, and the obstacle of by-product O₂ bubbles. To resolve this puzzle, a three-phase WOR system based on CO₂ (g)/dual-catalyst composite (s)/KOH (l) is adopted. At the three-phase interface, a high local concentration of CO₃ ^2-/HCO₃ ^- can form in the CO₂ adsorption unit and transfer to the WOR catalyst unit via the CO₃ ^2-/HCO₃ ^--mediated spillover effect. As a result, the largest H₂O₂ yield of 51.62 mM at 50 mA cm^-2 was realized, superior to that of the conventional two-phase system. Density functional theory (DFT) calculations, electrochemical and CO₂ adsorption tests, and in situ Fourier transform infrared spectra (FTIR) results jointly confirmed the larger adsorption amount of CO₃ ^2-/HCO₃ ^- ions, the spillover of CO₃ ^2-/HCO₃ ^- and their transformation to HCO₄ ^-, and the whole reaction processes from CO₂ adsorption to final H₂O₂ production at the three-phase interface. This is the first application of the three-phase design in WOR, which can provide guidance for efficient H₂O₂ synthesis in 2e^- WORs and can also be applied in other electrochemical WORs.