Transition of self-passivation and semiconductor property of titanium in the simulated environments of proton exchange membrane fuel cells

In this work, the passivation behaviors of titanium at various solution acidities are investigated in the simulated environments of proton exchange membrane fuel cells. The results show that there is a critical pH value to initiate the self-passivation of titanium, and a mathematic method based on the potentiodynamic polarization curve analysis is proposed to verify this value. The semiconductor type of the passive film changes from n-type to bipolar type, then to p-type as the pH increases, which can be explained by an n/p junction model. In addition, the relationship of the passive film thickness and pH is consistent with the prediction of point defect model.