Scanning electrochemical microscopy for the characterization of fuel cell components

The limited lifetime and severe degradation after long-term usage of polymer electrolyte membrane fuel cells (PEMFCs) are challenges that have to be overcome, if PEMFCs are to play the anticipated major role in a sustainable energy and transportation system based on green hydrogen. Therefore, analytical scanning methods to precisely characterize and understand the degradation and ageing mechanisms with high spatial resolution are essential. We are using and validating scanning electrochemical microscopy (SECM) as tool for detecting descriptors of the electrochemical performance of PEMFCs treated under different activation and ageing protocols. For this purpose, a pristine Nafion™ membrane, which is typically used as proton exchange membrane (PEM) in low temperature fuel cells, was activated and deactivated after well-defined protocols to demonstrate the fundamental suitability of SECM for investigating PEMFC components. Our results indicate that the impedance associated with the proton conductivity of the Nafion™ membrane as measured by SECM was dependent on the pretreatment of the membrane and increased in the following order: hot water < hydrochloric acid < sulfuric acid. The partial and complete deactivation of the membrane using Fenton’s reagent and barium hydroxide, respectively, could be spatially visualized with SECM as well. In addition, we investigated a PEM as part of a complete membrane electrode assembly in a fully functional PEMFC after accelerated ageing tests and could identify an increased local PEM impedance by SECM. All trends could be confirmed by electrochemical impedance spectroscopy (EIS). Moreover, we investigated a typical gas diffusion layer (GDL) of a PEMFC with SECM. As a result, the microporous side of the GDL showed a much lower impedance than its macroporous side, which is comprehensible since it agrees with the additional carbon black coating on the former side.