Titanium and titanium compounds in the bipolar plate/gas diffusion layer system of polymer electrolyte membrane fuel cells: manufacturing methods, surface treatments and properties

Abstract

Titanium (Ti) is widely distributed in the Earth's crust in the oxide form. The two main properties of Ti are high corrosion resistance and strength-to-density, the highest of any metallic element. Ti and Ti compounds are widely used in polymer electrolyte membrane fuel cells (PEMFCs), playing various roles. In this review, the utilization of titanium and titanium compounds in the bipolar plate/gas diffusion layer system of PEMFCs is presented and discussed as well as the manufacturing methods and surface treatments, with particular attention to the corrosion resistance and the interfacial contact resistance. The aim of this work is to highlight that titanium can effectively replace the commonly used bipolar plate (BP) materials, such as graphite and stainless steel, and gas diffusion layer (GDL) carbon-based materials. The key findings are the new manufacturing methods of BP and GDL materials and the high corrosion resistance and low interfacial contact resistance of coated Ti BPs. The value of the key parameters of coated Ti, that is, the corrosion current density (I_corr) and the interfacial contact resistance (ICR), meeting DOE requirements, make Ti a highly competitive material suitable for its use as BP material. The use of carbon-free integrated Ti-based BP/GDL systems formed by Ti BPs, either uncoated or coated by Ti compounds, and Ti GDL is a key point that is to be developed. It should be noted that the use of Ti as BP material is only partially discussed in previous reviews, but there are no reviews that analyze in depth the use of Ti both as BP and GDL material like this one.