Kinetic model of the electrochemical oxidation of graphitic carbon in acidic environments†
The electrochemical oxidation of graphitic carbon results in the performance decay of electrochemical systems such as aqueous, acidic fuel cells, redox-flow batteries, and supercapacitors. An electrochemical mechanism and numerical model is proposed to explain long-standing questions. The model predicts carbon weight loss and surface oxide growth as a function of time, temperature, and potential. Experimentally observed phenomena are discussed and analyzed using the numerical model. Three mechanisms are concluded to contribute to the current decay commonly observed during electrochemical oxidation: mass loss, reversible passive oxide formation, and irreversible oxide formation. Although reversible passive oxide formation governs the current decay under potentiostatic oxidation, a reduction in the equilibrium catalytic oxide is the most significant decay mechanism under potential cycling. Finally, the model is used to determine the change in active site concentration resulting from high-temperature heat treatment of carbon black.