Deconvoluting OER and MOR Kinetics on (1 wt %)r-GO@NiCrFe-BDC/NF via Operando Electrochemical Impedance Spectroscopy and Distribution of Relaxation Times Analysis

The sluggish oxygen evolution reaction (OER), with its high theoretical potential (1.23 V vs RHE), complex four-electron transfer pathway, and substantial activation energy barrier, remains a major obstacle to the efficiency and cost-effectiveness of water electrolysis. Replacing OER with thermodynamically favorable anodic reactions involving more readily oxidized organic molecules (methanol) offers a promising strategy to reduce energy consumption. Here, a (1 wt %)r-GO@NiCrFe-BDC nanocomposite was grown on nickel foam via a solvothermal route, requiring a lower applied potential of ∼1.439 V vs RHE to acquire a current density of 25 mA/cm2 for methanol electrooxidation compared to the oxygen evolution reaction (∼1.52 V vs RHE @ 25 mA/cm2). The r-GO was used at ultralow loading (1 wt %) as a conductivity-enhancing additive embedded within the NiCrFe-BDC framework rather than as an exposed carbon electrode. The electrochemical investigations reveal the distinct reaction kinetics of the oxygen evolution reaction and methanol electrooxidation. Notably, the methanol oxidation reaction (MOR) mechanism remains a subject of considerable ambiguity according to previously reported works. In this study, operando electrochemical impedance spectroscopy and distribution of relaxation time analysis (DRT) are applied to probe the hidden reaction kinetics (i.e., charge transfer, ion diffusion, adsorption/desorption, double-layer charging, and mass transport limitations) of the oxygen evolution reaction and methanol oxidation reaction. Systematic modulation of applied voltage and operating temperature enables the precise deconvolution of overlapping electrochemical processes through their characteristic relaxation times, thereby elucidating the distinct reaction kinetics governing the OER and MOR.