Demonstrating the absence of metal ion contamination in operando PEM fuel cells utilizing unmodified stainless steel bipolar plates

Using stainless steel as material for bipolar plates (BPPs) in proton exchange membrane fuel cells (PEMFCs) carries a perceived risk of corrosion and subsequent metal ion contamination of the membrane electrode as-sembly (MEA). However, assessments in literature on this hazard to PEMFC systems have been based on ex-situ corrosion studies, where general assumptions made on the BPP environment might not be a correct simulation of real on-site conditions. In this contribution, uncoated BPPs from stainless steel grades 304 L, 316 L and 904 L were subjected to in-situ hybrid endurance/stress testing to simulate realistic conditions in operating fuel cell systems and re-evaluate the need of additional corrosion protection. A post analysis of the plates showed no signs of surface dissolution on any of the tested samples and the concentration of iron in the MEA averaged 7 to 10 ppm for uncoated samples and 7 to 11 ppm for coated and graphitic reference tests, displaying a negligible amount of trace metals compared to critical thresholds found in literature. Contact resistance values were stable for all samples and observable changes in cell performance and voltage degradation was confirmed to be un-related to the presence of uncoated bipolar plates. The combined effects of decoupling of bipolar plate surface potentials from electrode potentials and operational control of stable gas flow compositions to sustain stainless steel surface passivation, were identified as explanation for the experimentally observed corrosion resistance of uncoated stainless steel plates in PEMFCs.

Automated summary

The use of stainless steel as bipolar plates in proton exchange membrane fuel cells (PEMFCs) has been a concern due to the risk of corrosion and metal ion contamination. Previous studies on this hazard have relied on ex-situ corrosion assessments which may not accurately represent real operating conditions. In this study, uncoated stainless steel bipolar plates were subjected to in-situ hybrid endurance/stress testing to simulate realistic conditions and re-evaluate the need for additional corrosion protection. The results showed no signs of surface dissolution and negligible trace metal concentration in the membrane electrode assembly (MEA). Contact resistance values were stable and changes in cell performance and voltage degradation were unrelated to the presence of uncoated bipolar plates. The corrosion resistance of uncoated stainless steel plates in PEMFCs was attributed to decoupling of bipolar plate surface potentials from electrode potentials and operational control to sustain stainless steel surface passivation.