Electrophoretic deposition of polypyrrole/Vulcan XC-72 corrosion protection coatings on SS-304 bipolar plates by asymmetric alternating current for PEM fuel cells

Abstract

In this study, corrosion protection composite films composed of polypyrrole (formed from the electropolymerization of pyrrol monomer) and Vulcan XC-72, labeled as PPy-C, were deposited on SS-304 substrates by EPD using an asymmetric AC signal (AAC) in acetone and acetone:methanol solutions. Prior to deposition, Vulcan powders were functionalized in order to create functional groups that develop a negative surface charge. Under the applied electric field, both pyrrole monomer and carbon colloidal particles migrated simultaneously toward the SS anode surface to create the corrosion protection PPy-C coatings. The effect of applied voltages (50, 70, 90 and 120 V) and deposition time (2, 6, 10 and 15 min) on the film characteristics was evaluated. The coatings were analyzed by SEM and the results showed improved characteristics of the films deposited by AAC, in terms of homogeneity and porosity, compared to samples prepared by a continuous DC process. Polarization curves were conducted in order to evaluate the corrosion characteristics of the bipolar plates in 0.1 M H2SO4 at room temperature. The experimental results indicated that the PPy-C composites significantly enhanced the corrosion resistance of the SS substrates. For example, the T1 sample increased the corrosion potential by about 541 mV and decreased the corrosion current density by two orders of magnitude, compared to uncoated SS. FTIR studies confirmed the formation of PPy after electropolymerization of the pyrrole monomer under the EPD process. Even though this characterization has been carried out in a half cell, it has been proposed that the PPy-C-coated SS bipolar plates may find application in the acidic atmosphere of PEMFCs.