The origin of the hysteresis in cyclic voltammetric response of alkaline methanol electrooxidation

The mechanism of the alkaline methanol electrooxidation reaction on platinum is complex and not fully understood. However, a better understanding will facilitate reaching the theoretical performance of an alkaline methanol fuel cell. Cyclic voltammetry is a often used method to investigate the mechanism of electrochemical reaction. The cyclic voltammogram of methanol electrooxidation show a potential hysteresis between the oxidation peaks in the forward and backward scan. The origin of this hysteresis has not been fully clarified. By means of parameter variations, such as the upper potential or the starting point of the CV measurements, and by physicochemical modeling, we investigate the formation of platinum oxides as a possible cause of this behavior. The experiments show that the formation of platinum oxides is more likely to cause the hysteresis than strongly adsorbed intermediates which are formed during the forward scan. The simulation includes the formation of platinum oxide species and supports the experimental results that the hysteresis is due to the formation and reduction of platinum oxides. Besides, the simulation reveals that in the investigated potential area different oxide forms are present.