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Chemical membrane degradation in polymer electrolyte membrane fuel cells operated under real conditions is often accompanied and affected by Pt catalyst degradation. This study investigates the effects of both artificially impregnated Pt particles and Pt migration on chemical membrane degradation are numerically investigated. For the first time, the impact of Pt migration is numerically analyzed. Membrane structural changes with coupled chemical membrane and Pt degradations are proposed. For Pt particles that are artificially impregnated in the membrane, yielding a Pt content of up to 50 mol% Pt, the membrane degrades at the fastest rate at moderate Pt contents (2 mol% Pt). The impregnated Pt particles promote the conversion of Fe3+ to Fe2+, which adversely impacts the membrane durability. The decrease in Pt content leads to reduction in both the Fe2+ conversion time and trend. In comparison, the naturally precipitated Pt particles in the membrane from the degraded Pt catalysts in the CL, have demonstrated a Pt content consistently lower than 2 mol% Pt. As a result, the chemical degradation rate of real fuel cells accelerates significantly with increasing Pt particle concentration. The chemical degradation rate increases with the gas solubility at the pore/electrolyte interface. With higher gas solubility, the peak location of chemical membrane degradation shifts from the anode side to the cathode side. • The effect of Pt migration on chemical membrane degradation is considered. • The Pt particles favor the Fe2+ state that is harmful to membrane durability. • The membrane degrades fastest at 2 mol% of impregnated Pt particles. • The migrated Pt band has low Pt content and accelerates membrane degradation. • The site of peak degradation varies with gas diffusion resistance to the Pt sites. [ABSTRACT FROM AUTHOR]

As a critical electrochemical reaction region of the proton exchange membrane fuel cell (PEMFC), the cracking issue of the catalyst layer (CL) considerably affects the performance and durability of the PEMFC. However, the impact of chemical ionomer degradation on CL cracking has not been comprehensively revealed. This study investigates the effect of chemical ionomer degradation on CL cracking through accelerated stress tests, characterization, and theoretical analysis. The results indicate that the increasing chemical degradation degree facilitates CL cracking. The CL with the most severe chemical degradation has a single total crack length increment of 1.97 times for the novel CL under the same degree of mechanical degradation. CL fracture resistance analyses reveal that the decrease in interface fracture resistance is the predominant impulse in accelerating CL cracking. Furthermore, the cell voltage reduction of the CL with the most severe chemical degradation during mechanical degradation is 34.22 mV at the current density of 1800 mA cm−2, which is 1.82 times for the fresh CL. The increment of activation resistance and mass transfer resistance are the main causes of the larger cell performance loss. The above findings emphasize the significance of high interface fracture resistance in inhibiting CL cracking and offer theoretical support for analyzing post-operational CL cracking. • Accelerated crack propagation mechanism under joint chemical and mechanical degradations is revealed. • The interface fracture resistance is proved to be the most predominant. • The fracture resistance of the catalyst layer is characterized by a multi-scale measurement method. • Theoretical basis for post-operational catalyst layer cracking analysis is proposed. [ABSTRACT FROM AUTHOR]

A new method to accelerate pore-scale simulation of porous electrodes is presented. The method combines the macroscopic approach with pore-scale simulation by decomposing a physical quantity into macroscopic and local variations. The multiscale method is applied to the potential equation in pore-scale simulation of a Proton Exchange Membrane Fuel Cell (PEMFC) catalyst layer, and validated with the conventional approach for pore-scale simulation. Results show that the multiscale scheme substantially reduces the computational cost without sacrificing accuracy. [ABSTRACT FROM AUTHOR]

The continuous chemical degradation of the polymer membrane in polymer electrolyte fuel cells causes membrane pinhole formation, therefore substantial increase in the gas cross-over flux. In this paper, a numerical method to simulate the pinhole formation process during chemical degradation is proposed. The method assumes that a membrane pinhole is formed by connected local micro-pores, which are generated owing to the mass loss during chemical membrane degradation. In addition, pinhole formation is combined with reduction of the membrane thickness to account for the membrane structure changes. A dynamic chemical degradation model that incorporates the effects of membrane structure changes is validated against the experimental results of the accelerated stress test. Results confirm the proposed method increases the accuracy of the chemical degradation model in predicting the macroscopic properties, including cumulative mass loss, hydrogen cross-over and open circuit voltage. Formation of pinhole starts from the anode, where degradation is more severe, and propagates to the cathode. The model also systemically studies the effects of temperature, pressure, and relative humidity on chemical degradation. The degradation rate increases with elevated temperatures and pressures. The degradation is shown to be more severe at moderate relative humidity, and the comparison with experimental findings are discussed. • A method to simulate pinhole formation during chemical degradation is proposed. • The method improves the accuracy of the chemical degradation model. • Hydrogen cross-over, fluoride mass loss and open circuit voltage are simulated. • Chemical degradation accelerates with temperature and pressure. • Chemical degradation is more severe at moderate relative humidity. [ABSTRACT FROM AUTHOR]