So far, most of the AST protocols were designed for commercial polymer electrolyte membrane fuel cells (PEMFCs) which consist on Pt-based catalysts, carbon supports and Nafion membranes. In the case of other catalysts, supports and membranes, specifically in AFCs, these ASTs become irrelevant due to the different chemical and electrochemical properties of the different components. For example, in some of the US-DOE ASTs, the electroactive surface area (ECSA), an indication of the catalysts activity, of Pt-based catalysts is measured from the hydrogen adsorption/desorption peaks: this cannot be done with non-precious group metal catalysts since most of them do not adsorb hydrogen. Hence, ASTs need to be considered as case sensitive, or at least divided into categories of materials, since not all fuel cells are composed of the same materials and/or operate under the same conditions. Therefore, other methods and measurable parameters need to be found in order to assess the catalyst degradation in such cases. Here, we developed the methodology which will allow groups who are studying non-conventional materials for fuel cells to study the stability and durability of their catalysts and supports, develop case-sensitive ASTs for their fuel cells in general and for AFCs in particular.
In this work a wide array of methods are used for testing non-precious group metal catalysts and support degradation alkaline fuel cell cathodes. In this case study, we used a cathode composed of a pyrolyzed non-precious metal group catalyst (NPMGC) on activated carbon. The vulnerabilities of the cathode components were studied in order to develop the methodology and design an accelerated stress test for NPMGC-based cathode in alkaline environment. Cyclic voltammetry (CV), chronoamperometry (CA) and impedance spectroscopy (EIS) were used to characterize the electrochemical behavior of the cathode and to follow the changes that occur as a result of exposing the cathodes to extreme operating conditions. Rotating ring disk electrode (RRDE) was used to study the cathodes kinetics; Raman spectroscopy and X-ray fluorescence (XRF) were used to study the structural changes in the electrode surface as well as depletion of the catalysts’ active sites from the electrode. The changes in the composition of the electrode and catalyst were detected using X-ray diffraction (XRD). For the first time, we show that NPMC degrade rapidly at low operating potentials whereas the support degrades at high operating potentials. We developed a tailor-made AST for the studied electrodes based on real operating statistics and operating conditions.