Corrosion resistance of a tungsten modified AISI 430 stainless steel bipolar plate for proton exchange membrane fuel cells

Abstract

In order to improve the corrosion resistance of AISI 430 stainless steel (430 SS) as a bipolar plate for proton exchange membrane fuel cells (PEMFCs), a tungsten diffusion layer has been successfully prepared on the AISI 430 SS samples using a plasma surface diffusion alloying technique. The tungsten diffusion-modified 430 SS (W-modified 430 SS) has a black surface and a tungsten diffusion layer with a thickness of 7–8 μm. X-ray diffraction data shows that there is only the body-centered-cubic tungsten phase on the surface of the W-modified 430 SS. In addition, the average contact angle with water for W-modified 430 SS is 93.5°, demonstrating the better hydrophobicity of its surface compared with the untreated one with an average contact angle of 69.6°. The electrochemical behavior of W-modified 430 SS is investigated in the simulated anode environment of a PEMFC (0.05 M H₂SO₄ + 2 ppm HF + 0.01 M NaCl solution at 70 °C). Potentiodynamic polarization, potentiostatic polarization and electrochemical impedance spectroscopy measurements reveal that the W-modified diffusion layer considerably improves the corrosion resistance of the 430 SS specimen compared with the untreated one. The corrosion current density of W-modified 430 SS is maintained at 2–3 μA cm⁻² under the simulated anode conditions. Moreover, no obvious pitting generates on the surface of W-modified 430 SS after 4 h of potentiostatic testing, while serious corrosion occurs on the surface of untreated 430 SS.