Exploring PANI-TiN Nanoparticle Coatings in a PEFC Environment: Enhancing Corrosion Resistance and Conductivity of Stainless Steel Bipolar Plates

Electrochemically-deposited polymer-metal composites, although explored for various uses, have only recently attracted attention for metallic bipolar plates used in fuel cells. Utilising a facile electrochemical deposition process, composite polyaniline and titanium nitride nanoparticle (PANI-TiN) coatings of varying thickness (5–50 cyclic voltammetry cycles) and composition (TiN nanoparticle concentration, 0.1 g L−1 and 0.5 g L−1) were deposited on stainless steel 304L (SS304) substrates. As compared to the pristine PANI coatings, which displayed an interfacial contact resistance (ICR) value of 367.5 mΩ cm2 and corrosion resistance (Ecorr) of 214 mVSHE, the composite PANI-TiN0.5 coatings displayed significantly reduced ICR values of 32.6 mΩ cm2 while maintaining similar corrosion resistance. The superior properties of these thin (~10 nm) composite coatings with low TiN loading (0.05–0.1 mg cm−2) show potential for further improvement in ICR with the possible use of higher TiN (or slightly lower PANI) concentrations. The study also demonstrated an interesting dynamic between PANI and TiN simultaneous deposition where the concentration of TiN NPs negatively affects the deposition rate for PANI, allowing the deposition of even thinner PANI coatings and possibly enabling control over the composition of the composite coating. The TiN NPs not only impart better conductivity for use as bipolar plates but, at higher loading, also assist PANI in enhancing corrosion resistance. Even for the lowest number of coating cycles (five cycles), the PANI-TiN0.5 composite films showed a remarkable 48 mV shift towards more positive/higher corrosion potential (Ecorr = 5 mVSHE) with respect to PANI (Ecorr = −57 mVSHE). The coatings demonstrated a reduction in corrosion current density to values of ~0.5 μA cm−2 achieving beyond the DoE 2020 target of 1 μA cm−2.