A novel carbon coating by electrochemical deposition in deep eutectic solvent with the assistance of ammonium chloride for stainless steel bipolar plates

In this work, pulse electrodeposition method was proposed to directly deposit amorphous carbon coating (ACC) onto 316L stainless steel substrate in choline chloride-ethylene glycol deep eutectic solvent (DES) mixed with ammonium chloride (NH4Cl) to fabricate bipolar plates. The obtained dense ACC has a thickness of similar to 400 nm. Potentiodynamic and potentiostatic polarization tests demonstrated that the corrosion current density of ACC coated 316L steel was of the order of 10(-7) A cm(-2) in the simulated proton exchange membrane fuel cells (PEMFC) working environment, and the self-corrosion potential of the coating positively shifted by 0.4V, indicating a significant improvement on corrosion resistance of the coated steel plate due to excellent electrochemical stability of ACC. The Rockwell C indentation test showed that the as-obtained ACC was strongly bonded to the substrate and also had high in-plane strength. Further numerical simulation and comparison experiments showed that C was chemically bonded with Fe in the substrate, which was boosted by the assistance of NH4Cl. The intact and strong bonding between ACC and the substrate is highly helpful to improve corrosion resistance. The success in coating stainless steel plate with ACC by pulse electrodeposition method provides a promising alternation for coating of proton exchange membrane electrolyzer cell (PEMEC) and PEMFC metal bipolar plates.