Comparing Methods for Quantifying Electrochemically Accumulated H2O2

There is an increasing interest in distributed hydrogen peroxide (H2O2) production through catalytic electrochemical reactions, such as the two-electron oxygen reduction and two-electron water oxidation reactions. Benchmarking the performance of electrocatalysts for these reactions requires accurate measurement of H2O2 concentrations. The concentration of H2O2 in electrochemical systems is commonly determined by three methods: UV-vis spectrophotometry, titration, and colorimetric test strips. However, there is a lack of detailed experimental protocols for using these three methods, and their accuracy under various electrochemical conditions has not been established. Herein, we first discuss reaction mechanisms and propose standard experimental procedures for all three methods. Then, we compare each method based on temporal stability, interference effects, sensitivity to pH, and electrolyte versatility. Finally, we report our blind study results on the accuracy of each measurement method across the concentration range of interest (5-1000 ppm). We find that the UV-vis method with the cobalt-carbonate assay is highly robust and yields a relative measurement error below 5% across the entire H2O2 concentration range studied. Titration with KMnO4 offers comparable error metrics to UV-vis when the H2O2 concentration is above 150 ppm. Colorimetric strips tend to be inaccurate under many conditions and should primarily be used as a "semiquantitative" means of measurement. These results will guide the selection and implementation of methods to measure accumulated H2O2 concentrations in various electrochemical systems.