Mechanistic pseudo-two-dimensional modeling of redox-mediated electrochemical reduction of metronidazole at cobalt oxide nanostructured electrodes

Abstract

The electrochemical reduction of metronidazole at nanostructured electrode interfaces involves a complex interplay of mass transport, electron-transfer kinetics, and redox mediation within the catalytic layer. In this work, a mechanistically grounded pseudo-two-dimensional (P2D) modeling framework is developed to quantitatively describe metronidazole reduction at a cobalt oxide nanoparticle-modified glassy carbon electrode. The model explicitly couples diffusion in the electrolyte with effective diffusion, Butler–Volmer kinetics, and dynamic Co²⁺/Co³⁺ redox mediation within a porous CoOx nanolayer, enabling spatially resolved analysis of transport–reaction interactions while retaining computational efficiency. The simulations successfully reproduce key experimental features, including cathodic peak enhancement, reduced overpotential, and diffusion-controlled current behavior. Quantitative analysis reveals that CoOx surface modification leads to nearly an order-of-magnitude increase in the effective heterogeneous rate constant compared with the bare electrode. The results further demonstrate that catalytic enhancement arises from dynamic redox-state evolution and spatially distributed reaction zones rather than from increased surface area alone. In addition, the model identifies an optimal CoOx layer thickness, beyond which internal mass transport limitations reduce catalyst utilization. Overall, the proposed P2D framework provides a robust and generalizable platform for mechanistic interpretation and rational design of high-performance nanostructured electrochemical sensors.