Unveiling the Impact of Carbon Corrosion on the Degradation of Fe-N-C Catalyst Layers in Alkaline Media

Abstract

One of the most promising candidates to replace platinum group metal catalysts for oxygen reduction reaction (ORR) in fuel cells (FCs) is the sub-class of iron-nitrogen-carbon (Fe-N-C) catalysts. However, Fe-N-C materials considerably suffer from varied degradation mechanisms. [1-2] Compared to FC operating conditions, start/stop events where the cathodes experience anodic potential may be more damaging due to the carbon corrosion phenomenon. [3] The correlation between carbon corrosion and Fe dissolution rates has been reported in aqueous model systems in acidic media. [3] However, different carbon corrosion mechanisms are reported for acidic and alkaline media. [4] While anion-exchange membrane FCs (AEMFCs) have gained increased attention, studies on the effects of carbon corrosion on realistic AEMFC Fe-N-C catalyst layers are still missing.In this work, using a gas diffusion electrode (GDE) half-cell coupled with inductively coupled plasma mass spectrometry (ICP-MS), [5] we observed that the rate of Fe loss significantly accelerates with rising potential (E > 1.0 VRHE), commonly experienced during the start/stop events. Increased temperature intensifies the rate of Fe leaching during carbon corrosion (see Figure 1), while the gas atmosphere (Ar or O2) shows a negligible influence. On the contrary, the subsequent Fe deposition and the drop of ORR activity depend on the presence of O2 and the varied temperature. Combining in situ and post-mortem analyses, we report how carbon corrosion in alkaline media degrades Fe-N-C catalyst layers in various atmospheres and at different temperatures. These insights can contribute to rational designs of AEMFCs' start/stop protocol and more robust Fe-N-C materials. Figure 1. Fe-N-C demetallation during anodic potential holds (1.0 - 1.5 VRHE) in O2-saturated alkaline (0.1 M NaOH) environment at 22 ± 2 and 62 ± 2 ℃. (A) Potential profile. (B) The Fe dissolution rate normalized to catalyst loading.