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High-oxygen-permeability ionomers (HOPIs) are being actively developed to enhance the performance and durability of high-power polymer electrolyte membrane fuel cells (PEMFCs). While methods for evaluating binder performance are well-established, techniques for assessing binder durability and measuring its degradation in situ during the AST process remain limited. This study examines the distribution of relaxation times (DRT) and Warburg-like response (WLR) methods as in situ analysis techniques during the catalyst-accelerated stress test (AST) process. We conducted catalyst-ASTs (0.6–0.95 V cycling) for 20,000 cycles, monitoring changes using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV). Contrary to expectations, during the catalyst-AST, the ion transport resistance of the binder decreased, indicating no binder degradation. Scanning electron microscopy/energy dispersive spectrometer (SEM/EDS) analysis revealed that the degradation rate of the catalyst and the support was relatively higher than that of the binder, leading to a reduction in catalyst layer thickness and improved binder network formation. By applying the DRT method during the catalyst-AST process, we were able to measure the increase in oxygen reduction reaction (ORR) resistance and the decrease in proton transport resistance in situ. This allowed for the real-time detection of the reduction in catalyst layer thickness and improvements in ionomer networks due to catalyst and support degradation. These findings provide new insights into the complex interplay between catalyst degradation and binder performance, contributing to the development of more durable PEMFC components. [ABSTRACT FROM AUTHOR]

The open cathode polymer electrolyte membrane fuel cell stack has some challenges in performance and durability. Especially, study on the durability of open cathode stacks remains insufficient, and there is no established evaluation method for open cathode stack. In this study, 13-cell open cathode stack is conducted startup/shutdown (SU/SD) constant current (CC) and SU/SD load cycle (LC), and polarization curve and electrochemical impedance spectroscopy of stack changes are observed. After the durability test protocol, the stack is dismantled, and the cause of degradation was analyzed using cyclic voltammetry, distribution relaxation times (DRT), X-ray diffraction (XRD), and transmission electron microscopy (TEM), depending on the positions of the cell and membrane electrode assembly. The SU/SD LC protocol shows over 40 % degradation in stack performance with 800 cycles fewer durability test than the SU/SD CC protocol. As a result, The SU/SD LC protocol shows a 44 % acceleration compared to the SU/SD CC protocol, resulting in a reduction of evaluation time by 127 h. Based on electrochemical surface area, double layer capacitance, XRD, and TEM analysis results, it is determined that the accelerated degradation of SU /SD LC protocol is caused by a combination of catalyst and catalyst support degradation induced Ostwald ripening and agglomeration. • Startup/shutdown (SU/SD) test protocols were conducted on the open cathode stack. • The load cycling (LC) accelerated the degradation rate of SU/SD protocol by 44 %. • Load cycling promoted ECSA decrease and catalyst particle growth at the outlet. • Degradation of the binder ionomer was observed at the outlet through DRT analysis. • The SU/SD LC protocol accelerated the catalyst layer degradation of the outlet. [ABSTRACT FROM AUTHOR]

In PEMFCs, a stack performance degradation can vary depending on the materials of each component, cell position, and membrane electrode assembly region. Therefore, to understand stack degradation, it is necessary to conduct durability studies using various stacks. This study investigates the causes of degradation in a Pt–Co catalyst-based stack during long-term operation. A 20-cell stack is operated dynamic load cycle for 2000 h. After the durability test, the stack is dismantled, and subjected to the electrochemical analysis. Significant decreases in open circuit voltage are commonly observed at the air inlet of each cell, confirmed to be due to membrane degradation through changes in hydrogen crossover current density and membrane thickness. At air outlet, performance decreases due to ohmic loss and mass transfer are more pronounced. It is confirmed that Co leached from catalyst contaminates the membrane and catalyst layer, resulting increase of ohmic resistance and mass transfer resistance. • A Pt–Co based 20-cell stack was subjected to a dynamic load cycle for 2000 h. • The higher the gas concentration region, the more membrane degradation was observed. • The Co leached from Pt–Co catalyst contaminates the membrane and catalyst layer. • The main cause of the performance decay was Co contamination. [ABSTRACT FROM AUTHOR]