Towards More Durable Fe-N-C Catalysts—Understanding Degradation Mechanisms of Active Sites and Carbon Structure

In pursuit of more sustainable materials for energy production, doped-carbon, single-atom catalysts have taken hold as prospective candidates to replace traditional noble metal catalysts for energy conversion technology. Herein, we report on using iron and nitrogen-doped carbon, denoted as Fe-N-C, as a noble metal-free catalyst for oxygen-depolarized cathodes in HCl electrolysis to replace the state-of-the-art noble metal catalyst, Rh_xS_y. While Fe-N-C shows high intrinsic oxygen reduction activity, the durability and degradation of the material in HCl electrolysis devices have yet to be studied.<br/>Fe-N-C has been shown to have high resistance to anion poisoning and improved performance over commercial platinum catalysts in HCl electrolysis. Fe-N-C achieves a current density of 0.5 A/cm² at 1.38 V. This surpasses Rh_xS_y by 0.1 V, allowing for lower power requirements while producing the same amount of chlorine. We have developed a scalable method to bulk synthesize Fe-N-C with high oxygen reduction activity (1). To fully realize its potential, Fe-N-C is subjected to accelerated stress tests (ASTs) in uncontrolled shutdowns to observe the changes in electrochemical performance. In situ Raman spectroscopy, X-ray spectroscopy, and in situ ion probes are used to characterize changes in structure and active site density to elucidate the cause of performance decay. This work contributes to the evaluation of Fe-N-C structure during various stages of degradation. More notably, this process contributes considerably to the commercialization of Fe-N-C as a practical replacement for noble metal catalysts in HCl electrolysis.<br/><br/><b>References</b><br/>(1) Jingkun Li, Qingying Jia, Shraboni Ghoshal, Wentao Liang, and Sanjeev Mukerjee <i>Langmuir</i> <b>2017</b> <i>33</i> (37), 9246-9253