טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentStein Tomer
SubjectCorrosion Resistance and Durability Enhancement of
Metal Bipolar Plates (BP) Substrates via
Metal-Nitride Coatings
DepartmentDepartment of Materials Science and Engineering
Supervisor Professor Yair Ein-Eli


Abstract

In an everlasting effort to produce cleaner and more efficient energy sources, many have faith in Fuel Cells (FCs) and Proton Exchange Membrane Fuel Cells (PEMFC) in particular. Traditionally PEMFCs' Bipolar Plates (BPs) were made of graphite, but lighter, less expensive materials have more appeal in nowadays studies.

The most common candidates are stainless steels that have many advantages over graphite with one clear disadvantage - corrosion. Metal nitrides and titanium nitride (TiN) in particular are among the most extensively investigated coatings for PEMFC's BPs. Metal nitride coatings are commonly employed by various modifications of Physical Vapor Deposition (PVD), thus are prone to deposition defects that are inherent in PVD processes.

In the current work, we report on the integrity maintenance of TiN PVD coatings on American Iron and Steel Institute (AISI) 416, taking advantage of their similar Coefficients of Thermal Expansion (CTE). A combination of this sort is expected to reduce thermal stresses to a minimum, as well as related coating cracks. A thorough surface analysis including roughness evolution and surficial damage in the course of BP corrosion process along with an extensive electrochemical study was combined to investigate different initial surface pretreatments.

We discovered that in order to maintain prolonged durability and sustainability of TiN coated AISI 416 substrates under PEMFC's harsh electrochemical environment, we must prepare a very fine polished surface before deposition. Mirror-like polished surfaces had endured longer polarization times with minor surface damage as opposed to lower grade polished surfaces.