With recent advances especially beginning-of-life power density showing that direct competition with proton exchange membrane fuel cell technology is indeed feasible, the durability of the alkaline Membrane-Electrode Assemblies (MEAs), which had been largely set aside in the community, comes into focus as perhaps the definitive remaining challenge of the technology .
In order to understand AEMFC performance losses, most of the characterization methods presented in the literature use ex-situ tools for post-mortem characterization, which are very effective especially in selecting material components (durability of membranes and membrane/ionomer chemistry, choice of Gas Diffusion Layers, mechanical stability of catalyst particles and catalyst layer morphologies, delamination, etc. However, the need for in-operando methods to follow performance losses in real time, and in real fuel cell hardware, can be satisfied using in-situ electrochemical impedance spectroscopy (EIS).
In this study we will present EIS measurements coupled with polarization curves collected during stability tests, while modifying operation parameters specially chosen to interrogate selected limitations, and study their evolution with time in fuel cell durability tests.
We focus especially on the influence of two features of the AEMFC: Mass transport loss modes, of which three are available: hydrogen, oxygen and – uniquely to the alkaline polymer electrolyte system – water, which is a reactant in the AEMFC cathode. Second, we examine the role of PtRu, by now a widely used alkaline HOR electrocatalyst that demonstrates high activity, but in some cases can be subject to activity loss via partial surface oxidation. This work demonstrates the opportunity to use EIS as a real time characterization tool towards improved understanding of AEMFC stability challenges.