Mokpo National Maritime University

The effects of oxidation treatment on the electrochem. charactersitics and the interfacial contact resistance of CrAlN coatings were investigated for application to metallic bipolar plates of the polymer electrolyte membrane fuel cells.Three types of CrAlN-coated specimens were prepared: unoxidized, chem. oxidized and electrochem. oxidized specimens.On the surface of oxidized CrAlN coatings, defects such as micro-/nano-particles and pores were decreased, but the oxygen content increased.Compared with the unoxidized specimens, the chem. oxidized specimens showed lower corrosion c.d., a wider passive region, higher activation overpotential and faster stabilization.The electrochem. oxidized specimens exhibited the highest electrochem. stability because of the formation of an oxide film in defect regions, which prevented the penetration of corrosive ions.In the unoxidized specimens, corrosion initiated around micro-particle regions.This is attributed to the fact that the growth defects in the CrAlN coating layer caused crack propagation, thus creating a pathway for penetration and attack by corrosive ions.However, the CrAlN-coated specimens with defects sealed by the oxide film exhibited relatively superior corrosion resistance.The chem. and electrochem. oxidized specimens had an interfacial contact resistance of less than 10 mΩ·cm² under a compaction force of 138 N/cm² after potentiostatic polarization experiments

This research investigated the synergistic effects of heat and hydration treatments on the mech. and electrochem. characteristics of AlTiN-coated specimens.X-ray diffraction anal. presented no phase transitions due to such treatments.However, the intensity of the (Al,Ti)N crystalline phase weakened upon the interaction between the oxidation and hydration treatments.The addnl. TiN and TiO₂ crystalline phases were observedMost of the oxides that formed in the microparticles on the surfaces of the specimens were Ti oxides, which had both polygonal and needle-shaped structures.Polygonal Ti oxides, which are relatively stable in nature, were found in higher proportions in the specimens with hydration after heat treatment.Such specimens also exhibited superior mech. and electrochem. characteristics.This phenomenon is attributed to the pos. effect of the interaction between the rearrangement of lattice structures via heat treatment and the formation of oxide films through hydration treatment.In contrast, the specimens heat-treated after hydration suffered from the neg. effect of the treatments on each other, resulting in a slight degradation in mech. and electrochem. characteristics.Therefore, the appropriate sequencing of heat and hydration treatments is crucial to maximizing their effects.

In this study, we successfully synthesized nitrogen and sulfur-doped dual heteroatom graphene carbon nanosheets via a solution plasma process without thermal treatment, recognized for effectively promoting the oxygen reduction reaction (ORR) as non-precious metal catalysts.TEM images revealed large area nanosheets with a crumpled morphol., while EDS elemental mapping confirmed the uniform distribution of carbon, oxygen, nitrogen, and sulfur throughout the nanosheets.Addnl., powder XRD and Raman anal. suggested the presence of turbostratic stacking with an average of around three graphene layers in NSCNs.XPS results confirmed the successful incorporation of nitrogen and sulfur atoms into the graphene structure using our approach.Lastly, NSCNs exhibited lower ORR catalytic activity compared to 20 wt% Pt/C but demonstrated excellent electrochem. stability, highlighting their potential for elec. catalytic applications.