Process and challenges of stainless steel based bipolar plates for proton exchange membrane fuel cells

Proton exchange membrane fuel cell (PEMFC) powered automobiles have been recognized to be the ultimate solution to replace traditional fuel automobiles because of their advantages of PEMFCs such as no pollution, low temperature start-up, high energy density, and low noise. As one of the core components, the bipolar plates (BPs) play an important role in the PEMFC stack. Traditional graphite BPs and composite BPs have been criticized for their shortcomings such as low strength, high brittleness, and high processing cost. In contrast, stainless steel BPs (SSBPs) have recently attracted much attention of domestic and foreign researchers because of their excellent comprehensive performance, low cost, and diverse options for automobile applications. However, the SSBPs are prone to corrosion and passivation in the PEMFC working environment, which lead to reduced output power or premature failure. This review is aimed to summarize the corrosion and passivation mechanisms, characterizations and evaluation, and the surface modification technologies in the current SSBPs research. The non-coating and coating technical routes of SSBPs are demonstrated, such as substrate component regulation, thermal nitriding, electroplating, ion plating, chemical vapor deposition, and physical vapor deposition, etc. Alternative coating materials for SSBPs are metal coatings, metal nitride coatings, conductive polymer coatings, and polymer/carbon coatings, etc. Both the surface modification technologies can solve the corrosion resistance problem of stainless steel without affecting the contact resistance, however still facing restraints such as long-time stability, feasibility of low-cost, and mass production process. This paper is believed to enrich the knowledge of high-performance and long-life BPs applied for PEMFC automobiles.