HiPIMS-enabled Ti-doped amorphous carbon coatings for high-performance PEMFC bipolar plates

Amorphous carbon (α-C) coatings play a critical role in enhancing the electrical conductivity, corrosion resistance, and chemical stability of stainless steel bipolar plates in proton exchange membrane fuel cells (PEMFCs). However, traditional deposition methods, such as magnetron sputtering and chemical vapor deposition, suffer from limitations including suboptimal sp²/sp³ ratios, high residual stress, and insufficient mechanical durability, restricting their application. This study develops Ti-doped α-C coatings using a combined high power impulse magnetron sputtering (HiPIMS) and pulsed DC magnetron sputtering (PDCMS) approach to overcome these challenges. By varying Ti target power (0–1 kW), the microstructure, electrical properties, corrosion resistance, and mechanical performance of the coatings were systematically investigated. Ti doping increased the sp²/sp³ ratio and promoted low-resistivity carbide phase formation, reducing the interfacial contact resistance from 5.8 to 2.6 mΩ cm² (0.6 kW). At an optimal Ti target power of 0.6 kW, the coatings achieved excellent corrosion resistance, with a corrosion current density of 0.12 μA cm⁻². Additionally, mechanical properties were significantly enhanced, with hardness reaching 13.64 GPa and elastic recovery improving to 43 %. These findings demonstrate that Ti-doped α-C coatings not only address the limitations of traditional α-C deposition techniques but also offer a cost-effective, high-performance solution for stainless steel bipolar plates, advancing the commercialization of PEMFCs.