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

ABSTRACT Two‐electron water oxidation reaction (2e − WOR) mediated by (bi)carbonate (CO 3 2− /HCO 3 − ) is promising for anodic H 2 O 2 production. However, previous H 2 O 2 yields are usually unsatisfactory due to low local CO 3 2− /HCO 3 − concentration at the solid/liquid interface. These sluggish reaction rates mainly result from the restricted ion diffusion, and the obstacle of by‐product O 2 bubbles. To resolve this puzzle, a three‐phase WOR system based on CO 2 (g)/dual‐catalyst composite (s)/KOH (l) is adopted. At the three‐phase interface, a high local concentration of CO 3 2− /HCO 3 − can form in the CO 2 adsorption unit and transfer to the WOR catalyst unit via the CO 3 2− /HCO 3 − ‐mediated spillover effect. As a result, the largest H 2 O 2 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 CO 2 adsorption tests, and in situ Fourier transform infrared spectra (FTIR) results jointly confirmed the larger adsorption amount of CO 3 2− /HCO 3 − ions, the spillover of CO 3 2− /HCO 3 − and their transformation to HCO 4 − , and the whole reaction processes from CO 2 adsorption to final H 2 O 2 production at the three‐phase interface. This is the first application of the three‐phase design in WOR, which can provide guidance for efficient H 2 O 2 synthesis in 2e − WORs and can also be applied in other electrochemical WORs.