Nonlinear frequency response method for detecting cation contamination in proton exchange membrane water electrolysis

The dissolution of metallic components (such as catalysts, porous transport layers, and end plates) leads to ion contamination of the catalyst-coated membrane (CCM) and is one of the main degradation pathways in polymer electrolyte membrane water electrolyzers (PEMWEs). The ability to detect such a condition early on is critical for the widespread deployment of PEMWEs. We propose using a nonlinear frequency response (NFR) method to efficiently identify degradation caused by metallic ion contamination. To investigate internally generated metallic ion corrosion, we employed PEMWEs with gold‑coated aluminum end plates. Initially, gold-coated aluminum provided stable operation and lowered high‑frequency resistance. However, coating defects, inevitable during assembly/disassembly, formed an Al/Au galvanic couple, leading to accelerated corrosion. Post-mortem scanning electron microscopy and energy dispersive X-ray spectroscopy confirmed the presence of end plate base materials in the porous transport layer and CCM. Performance deterioration during PEMWE operation was monitored via polarization curves, anodic cyclic voltammetry (CV), and the NFR method. While CV remained stable, polarization and NFR revealed progressive degradation attributable to corrosion products contaminating CCM. The linear part of the NFR (impedance-consistent) quantified resistance increase, whereas the nonlinear signature shifted qualitatively, clearly distinguishing healthy from degraded cells. Physics‑based modeling indicated that cathode‑side contamination by corrosion products reproduces the observed nonlinear response. These results confirm that the NFR method is a promising diagnostic tool for PEMWE health monitoring. In practice, gold-coated aluminium has some limitations for use in commercial systems. Therefore, more robust coatings or alternative materials should be prioritised to avoid rapid failure.