A Review of Research Progress on Modified Coatings for Stainless Steel Bipolar Plates in Proton Exchange Membrane Fuel Cells

Proton exchange membrane fuel cells (PEMFCs) have become a core technology for the efficient utilisation of hydrogen energy due to their high energy conversion efficiency, zero pollutant emissions, and rapid start-up and shut-down capabilities. As a key component of the fuel cell stack, the performance of the bipolar plate directly determines the stack’s power density and service life. This review aims to synthesize the corrosion failure mechanisms of stainless steel bipolar plates, compare the principal modified coating systems in terms of corrosion resistance and electrical conductivity, evaluate their limitations against practical performance requirements, and identify research directions relevant to durable and scalable PEMFC bipolar-plate development. Stainless steel has emerged as the most cost-effective substrate material for bipolar plates due to its excellent mechanical properties, good stamping formability, and low cost. However, it is prone to corrosion in the high-temperature, acidic, and fluorine-containing operating environment of PEMFCs, leading to issues such as metal ion leaching that poisons the membrane electrode and increased interfacial contact resistance. These problems severely limit its large-scale application; surface-modified coatings represent a key technological approach to achieving a balance between corrosion resistance and electrical conductivity. This paper systematically elucidates the corrosion failure mechanisms of stainless steel bipolar plates under PEMFC operating conditions (pitting corrosion induced by passivation film dissolution, membrane electrode poisoning by metal ions, and increased interfacial contact resistance due to corrosion products) as well as the DOE performance evaluation criteria. It focuses on reviewing research progress in four major coating systems: carbon-based, transition metal nitride, and transition metal carbide multilayer composite coatings. Based on this, the paper analyses core challenges such as long-term service durability, consistency in large-scale production, and adaptability to extreme operating conditions. It identifies multi-component doping and high-entropy composition design, optimisation of multilayer gradients and biomimetic structures, development of low-cost continuous fabrication processes, and in situ failure mechanism studies as the primary future development directions, with the aim of providing guidance for the research, development, and industrialization of high-performance modified coatings for stainless steel bipolar plates.