An experimentally validated model for anodic H2O2 production in alkaline water electrolysis and its implications for scaled-up operation

Abstract

The anodic co-production of hydrogen peroxide (H2O2) during alkaline water electrolysis has gained interest as a sustainable alternative for anthraquinone oxidation. However, electrochemical H2O2 production is often studied with idealized laboratory setups to determine the H2O2 formation kinetics. In this work, we perform the reaction with industrially relevant operating principles using a flow cell with separately recirculating anolyte and catholyte. We then fit the data to an analytical model that we derive based on mole balances that accounts for anodic generation, anodic oxidation, and bulk disproportionation of H2O2, as well as electrolyte volumes and electrode surface area. We performed experiments at 100, 200, and 300 mA cm-2 to derive values for the reaction system. At 200 mA cm-2, we found a generation rate of 0.037 mmol min-1 cm-2 (FEH2O2 = 59%) and an anodic decomposition rate constant of 0.304 cm min-1, with a bulk disproportionation rate constant of 1.85 × 10-3 min-1. We successfully applied our model to two sources in literature to derive values for their systems as well. In all cases, the contribution of anodic oxidation of H2O2 was found to be the larger loss mechanism in comparison to bulk disproportionation. Using the analytical model, we show that decreasing the reservoir volume is a simple way to increase the H2O2 concentration over time. Further refinement of the model can be achieved through the use of mass transfer relationships based on electrolyzer geometries to describe the anodic oxidation of H2O2 in the mole balance equations.