Corrosion resistant metallic bipolar plate

#The present invention relates to components such as metal bipolar plates for proton exchange membrane (PEM) fuel cells and other chemical-to-electrical energy conversion devices, and more particularly to metal bipolar plates having thermally grown nitrided surface layers to enhance corrosion resistance thereof.

#Chemical-to-electrical energy conversion devices, especially PEM fuel cells, are of great interest as efficient, non-polluting power sources for automotive applications, and also for stationary applications such as distributed power sources for buildings and houses as well as portable power generation for consumer electronic devices. A major barrier to commercial application of this technology is the cost of the devices.

#A key component of the fuel cell design (and for electrochemical power generation devices in general, such as some battery designs) is the well-known bipolar plate, which serves to separate fuel and oxidant and to connect the cathode of one cell to the anode of the adjacent cell in a stacked series. The cost of the machined graphite bipolar plates in PEM fuel cells accounts for as much as 60% of the overall fuel cell stack costs. Metallic bipolar plates offer the potential for significantly lower cost since they can be formed by readily available and inexpensive conventional metal forming processes.

#FIG. 1 is a graph showing anodic polarization curves for binary bipolar plate material made in accordance with the present invention compared with other materials.

#FIG. 2 is a scanning electron photomicrograph showing a cross-section of Ni-50Cr (Cr 50%, balance Ni) nitrided at 1100° C. for 1 hr. in N2 in accordance with the present invention.

#FIG. 3 is a graph showing anodic polarization curves for ternary bipolar plate materials made in accordance with the present invention.

#For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above-described drawings.

#Bipolar plate and other components made with base metal-Cr substrates have a distinct advantage in forming a nitride or carbonitride layer for corrosion protection. As the nitride or carbonitride layer is grown, three distinct, beneficial, and unexpected advantages are manifest:

#1. Chromium nitrides and/or carbonitrides are formed preferentially over base metal nitrides and/or carbonitrides. The advantage is that chromium nitrides and carbonitrides are corrosion resistant, while the presence of base metal nitrides and carbonitrides would generally degrade corrosion resistance.