Titanium bipolar plates have emerged as pivotal components in proton exchange membrane (PEM) fuel cells due to their exceptional corrosion resistance, lightweight properties, and mechanical durability. However, the inherent limitations of titanium's native oxide layer-particularly its high electrical resistivity-necessitate advanced surface coatings to optimize performance. Modern coating technologies aim to address these challenges by enhancing conductivity, preventing electrochemical degradation, and ensuring long-term stability under the harsh operating conditions of fuel cells.
Conventional carbon-based coatings, such as graphite or diamond-like carbon (DLC), have shown vulnerabilities in mechanical adhesion and thermal expansion compatibility. In contrast, metallic coatings like transition metal carbides and nitrides (e.g., titanium nitride, chromium nitride) offer superior electrical performance but often suffer from defects such as microcracks or pinholes. Innovations in physical vapor deposition (PVD) techniques, including advanced magnetron sputtering and plasma-enhanced processes, now enable the fabrication of nanolayered architectures. These multilayered coatings minimize defect formation by disrupting columnar grain growth while maintaining low interfacial contact resistance.
A critical focus lies in resolving thermal expansion mismatches between titanium substrates and ceramic coatings. Gradient interlayers-engineered with compositionally graded metal-ceramic transitions-effectively mitigate stress-induced delamination. Surface pretreatment methods, such as plasma nitriding, further enhance adhesion by creating diffusion-hardened interfaces with nanoscale roughness. Post-deposition treatments, including laser surface modification, refine coating morphology to improve hydrophobicity and reduce microcrack propagation, thereby extending operational lifespan.
Electrochemical validation remains central to coating development. Accelerated testing under simulated PEMFC environments demonstrates that optimized coatings exhibit corrosion currents significantly lower than uncoated titanium, alongside stable interfacial resistance even after prolonged thermal cycling. Such advancements underscore the potential of titanium-based bipolar plates to meet stringent durability requirements in commercial applications.
Looking ahead, emerging trends emphasize intelligent coating systems. Self-healing mechanisms inspired by biological materials, machine learning-driven material design, and in-situ diagnostic sensors represent transformative approaches. Atomic layer deposition (ALD) is gaining traction for ultrathin, conformal coatings, while roll-to-roll manufacturing processes enhance scalability and cost-efficiency. These innovations align with global efforts to reduce fuel cell system costs, positioning titanium bipolar plates as enablers for the widespread adoption of hydrogen energy technologies in transportation and grid-scale storage. By integrating multidisciplinary advances in materials science and manufacturing, the next generation of coatings promises to deliver unprecedented reliability and performance, accelerating the transition to sustainable energy systems.
