(Digital Presentation) Transferability of a Modeled Cathode Accelerated Stress Test for Carbon Corrosion between the Membrane Electrode Assembly and the Rotating Disk Electrode

Abstract

The Polymer Electrolyte Membrane Fuel Cell (PEMFC) represents an indispensable technology to ensure the emission-free and sustainable mobility of tomorrow. The commercial viability of PEMFCs scales not only with the performance but also with the longevity of its components, especially the Membrane Electrode Assembly (MEA).One of the key degradation mechanisms of the MEA constitutes Starting-Up (SU) from an inactive (air/air situation) state as well as Shutting-Down (SD) from an active (H2/air situation) state. The onset of oxygen reduction along the H2/air gas front in the anode compartment of the fuel cell leads to a local potential rise at the cathode, which, among other things, promotes the parasitic Carbon Oxidation Reaction (COR) of the cathode catalyst support material. The COR can lead to a separation of the supported catalyst particles from the rest of the electrical network, thus, to a reduction of the Effective Catalyst Surface Area (ECSA), but also to an increasing mechanical instability up to the collapse of the catalyst layer. [1]In previous works, various approaches have been taken to translate real-world damage mechanisms into component-based and accelerated stress tests [2]. To investigate the degenerative effects of SUSD events on MEA corrosion stability, this work first demonstrates the transferability of degradation through a real gas exchange between air and hydrogen at the anode and a simplified but equivalent potential program (Figure 1) under inert conditions using an external power supply on an in-situ complete cell configuration over a common number of cycles. Subsequently, this potential program is repeated ex-situ using a thin-film coated Rotating Disk Electrode (RDE) in a three-electrode setup and an aqueous electrolyte at the same temperature as for the in-situ complete cell execution.The integration level comparison is intended to prove that the RDE is an important characterization strategy for degradation analysis, particularly due to its comparatively low complexity and timely and financial efficiency and may be fundamentally advanced over the expensive and time-consuming complete cell measurement.For this purpose, electrochemical measurement methods, such as Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS) using the transmission line model for a porous electrode, oxygen diffusion resistance and polarization characteristics at different operating parameters were conducted. In addition, morphological studies were evaluated with respect to Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS). It is shown that the electrochemical degradation according to the mentioned characterization methods can be transferred in very good approximation from the real gas exchange to the potential protocol on the in-situ complete cell and subsequently to the RDE half cell.