Negative resistance for methanol electro-oxidation on platinum/carbon (Pt/C) catalyst investigated by an electrochemical impedance spectroscopy

• To establish complete EIS model for methanol electro-oxidation on Pt/C catalyst.
• The model parameters make quantitative description for bifunctional mechanism.
• To determine the surface condition for negative resistance appearance.
• The results of negative resistance help understand general electrochemical systems.

The poisoning of Pt-based catalyst occurs generally during methanol electro-oxidation. Though traditional electrochemical techniques have probed these issues intensively, it is amazing to find that the negative resistance presents in the intermediate potential zone during an electrochemical impedance spectroscopy (EIS) measurement. Based on the chemical reaction analysis, we establish an EIS model and make some numerical analyses, thus determining the specific EIS shapes and equivalent circuits relating to various potential zones. These results not only compensate the drawback for traditional electrochemical approaches, but also reveal the dynamic adsorption of CO and OH species on Pt surfaces, providing a chance for understanding bifunctional mechanism towards quantitative manners. Significantly, we clarify that the negative resistance begins from the maximum catalysis of methanol electro-catalysis and ends in the initial passive state on Pt surfaces, offering a tool for further improvement. Interestingly, our discovery for negative resistance is consistent with that in general electrochemical system, facilitating its extension and direction in future.