The Role of Bicarbonate-Based Electrolytes in H2O2 Production through Two-Electron Water Oxidation

Abstract

Two-electron water oxidation (2e–WOR) is a promising route toward efficient production of a valuable product in H2O2. Recent attention has focused on developing new electrocatalysts for 2e–WOR, but the role of the electrolyte species in determining water oxidation selectivity and promoting 2e–WOR has not been established. Here, we use electroanalytical experiments to confirm the role of HCO3– as a selective 2e–WOR redox catalyst. We find minimal differences in H2O2 consumption pathways among common electrolytes, indicating that the role of HCO3– is to promote H2O2 production. Mechanistically, our rotating ring disk experiments show that H2O2 is not generated directly at the disk electrode in KHCO3 but formed after a time delay, suggesting electrolyte oxidation and subsequent hydrolysis as the promotional mechanism. Further electrochemical and spectroscopic experiments confirm this hypothesis, demonstrating anodic oxidation of carbonaceous electrolyte species occurs at Faradaic potentials relevant for water oxidation and that these species (likely HCO4– or C2O62–) subsequently oxidize water to H2O2 (t1/2 ≈ 5 min). The H2O2 production rate at 2.5 V vs RHE scales linearly with the concentration of HCO3–, confirming the catalytic role of HCO3– in 2e–WOR and suggesting the electrolyte can be leveraged to enhance electrochemical H2O2 production.