Enhancing Electrochemical Water Oxidation toward H₂O₂ via Carbonaceous Electrolyte Engineering

Electrochemical production of H2O2 from water is a promising route toward improving the value and utility of water electrolysis. Though several studies have demonstrated the superior performance of bicarbonate electrolytes (especially concentrated potassium bicarbonate, 2 M KHCO3), none have focused on systematically engineering the electrolyte to further improve H2O2 production. Here, we use chronoamperometry to investigate the impact of the bicarbonate and carbonate mole fractions, total dissolved inorganic carbon (DIC) concentration, and electrolyte cations on the selectivity and current density toward H2O2 at varying applied potentials. We identify a novel optimized electrolyte composition of 0.5 M KHCO3 and 3.5 M K2CO3 at a voltage of 3.25 V vs RHE that improves the faradaic efficiency toward H2O2 from 5% in 2 M KHCO3 to 45% on a fluorine-doped tin oxide anode. Correspondingly, the current density toward H2O2 production (JH2O2) increases from 0.38 to 4.7 mA/cm2, a 12-fold improvement. Moreover, the optimized electrolyte leads to more stable H2O2 production over time. Importantly, we find that the optimized electrolyte also improves the faradaic efficiency and H2O2 production rate when using other electrode surfaces (e.g., zinc oxide, bismuth vanadate, and titanium dioxide), demonstrating its general applicability. Our techno-economic analysis reveals that the optimized electrolyte reduces the cost of electricity necessary to produce a kilogram of H2O2 by over 85% in comparison to 2 M KHCO3 and the estimated electrolyzer thermal efficiency reaches ∼42% at 3.25 V vs RHE. Together, these results highlight the promise of electrolyte engineering to bring the production of H2O2 via water oxidation into practice.