Beyond the Classical Koutecky–Levich Analysis: Deconvoluting Parallel Pathways in Hydrogen Peroxide Electroreduction Reaction

This study introduces an adjusted Koutecky–Levich (A-K-L) framework to address the limitations of the classical K-L equation when applied to the hydrogen peroxide electroreduction reaction (HPRR). HPRR involves complex, parallel pathways: direct 2-electron reduction and indirect reduction through H2O2 decomposition to O2. We hypothesize that deconvoluting the individual contributions of each pathway will yield a more accurate understanding of HPRR kinetics, thereby enabling improved catalyst design for H2O2-based fuel cells. Our approach employs hydrodynamic chronocoulometry (HCC) to simultaneously determine H2O2 diffusion coefficients and bulk concentrations. By solving coupled mass transport equations for HPRR, we derive a general current-density equation analogous to the K-L equation but incorporating five key reactions: H2O2 reduction, decomposition, O2 reduction via both 4-electron and 2-electron pathways, and O2 desorption. The systematic simplification of this A-K-L equation reveals seven distinct mechanistic cases. Unlike the classical K-L equation, our framework explicitly accounts for parallel reaction pathways, overcoming the single-pathway assumption of traditional analyses. We validate this approach using Pt disk, Pt ink, and Au disk electrodes at varying H2O2 concentrations. Notably, Au exhibits exceptional selectivity for direct 2-electron H2O2 reduction with minimal decomposition, outperforming Pt-based electrodes. This methodology clarifies dominant reaction mechanisms and provides a practical tool for rapid catalyst screening and optimization, supporting the development of efficient, selective cathodes for H2O2 fuel cells. Overall, this work establishes both a theoretical foundation and a practical toolkit for analyzing complex, multi-pathway electrochemical systems where the classical K-L equation is inadequate.