Modeling of Potential Oscillation during Galvanostatic Electrooxidation of Formic Acid at Platinum Electrode

摘要

Oscillation during electrocatalytic oxidation of formic acid at Pt electrode under galvanostatic conditions in acidic electrolyte has been simulated based on a chemical model that involves three reaction pathways: (i) the indirect pathway via CO_(ad) formation (formic acid dehydration) and oxidation; (ii) a formate pathway, involving adsorption— desorption of bridged adsorbed formate and its oxidation; and (iii) a direct pathway with successive cutting of O—H and C—H bonds. We found that only when the contribution of formate oxidation to the total formic acid oxidation current is negligible do the simulated results reproduce well the experimentally observed oscillatory patterns for electrode potential and the coverage of CO_(ad) and bridge-bonded formate. It is found that the fast adsorption— desorption of both formate and OH_(ad) are responsible for the hidden negative impedance; the slow CO_(ad) formation and its fast oxidation at higher potentials lead to a positive impedance. The simulated results further support the conclusion that bridge-bonded formate is not the reactive intermediate for the major pathway of formic acid oxidation at Pt electrode.