Cr-implanted stainless steel bipolar plates in hydrogen fuel cells for enhanced electrical conductivity

Stainless steel is considered to be the most potential bipolar plate material in hydrogen fuel cells due to its thin thickness and low cost, but suffers from decreased electrical conductivity in long-time usage. Herein, the surface of 316L stainless steel (SS316L) is modified by the ion implantation of Cr with different accelerating voltages and ion implantation doses. The implantation of Cr brings in a substantial improvement in the surface electrical conductivity, which is due to the formation of Cr oxide, Cr₇C₃ and Cr₂₃C₆. In all cases, interfacial contact resistance (ICR) is decreased with the increased implantation doses. In the cathodic environment, the minimum value of ICR (14.89 mΩ·cm²) is obtained at an accelerating voltage of 20 kV. However, in the anodic environment, the minimum value of ICR (7.19 mΩ·cm²) is obtained at an accelerating voltage of 40 kV. This is because the passive layer is destroyed by hydrogen. Besides, the deeper distribution of the Cr₇C₃ and Cr₂₃C₆ facilitates the formation of a more stable conductive pathway, which decreases the ICR. Moreover, simulations are also performed to give atomistic insights into the radiation damage during the implantation process. The results show that the maximum radiation damage is caused at an accelerating voltage of 40 kV. The unveiled mechanisms of the modified layer in this work are expected to guide the surface modification of stainless steel bipolar plates.