Stability of Fe‐N‐C Catalysts in Acidic Medium Studied by Operando Spectroscopy

Abstract

Fundamental understanding of non-precious metal catalysts for the oxygen reduction reaction (ORR) is the nub for the successful replacement of noble Pt in fuel cells and, therefore, of central importance for a technological breakthrough. Herein, the degradation mechanisms of a model high-performance Fe-N-C catalyst have been studied with online inductively coupled plasma mass spectrometry (ICP-MS) and differential electrochemical mass spectroscopy (DEMS) coupled to a modified scanning flow cell (SFC) system. We demonstrate that Fe leaching from iron particles occurs at low potential (<0.7 V) without a direct adverse effect on the ORR activity, while carbon oxidation occurs at high potential (>0.9 V) with a destruction of active sites such as FeNx Cy species. Operando techniques combined with identical location-scanning transmission electron spectroscopy (IL-STEM) identify that the latter mechanism leads to a major ORR activity decay, depending on the upper potential limit and electrolyte temperature. Stable operando potential windows and operational strategies are suggested for avoiding degradation of Fe-N-C catalysts in acidic medium.

Air Breathing Cathodes for Microbial Fuel Cell using Mn-, Fe-, Co- and Ni-containing Platinum Group Metal-free Catalysts

“…While ORR pathways have been widely studied in both acidic [15], [16], [17], [18] and alkaline [19], [20], [21], [22] media, the kinetic mechanisms taking place in neutral media − in which MFCs usually operate − are not fully understood. Using the rotating ring disk electrode (RRDE) technique, it was recently shown that oxygen is reduced via a 2e − mechanism on carbon black and activated carbon [23], [24], where as a 4e − pathway is dominant for Pt [24] and Fe-based catalyst [25], [26].…”

Co-based heterogeneous catalysts from well-defined α-diimine complexes: Discussing the role of nitrogen

“…Among the various dopants, nitrogen attracted most interest [15,[20][21][22]. and applications of transition metal/N-doped graphene (NGr) based catalytic systems ranges from oxygen reduction reactions (ORR) [23][24][25][26], hydrogen evolving reactions (HER) [27,28], photocatalysis [29,30], oxidation [31][32][33][34][35][36][37][38], and reduction [39][40][41][42][43][44] reactions of organic molecules, C-C bond formation [45] to many others [46][47][48][49][50][51]. Hence, merging rationally-designed suitable modified supports with cheap transition metals permits access to the design of active, selective and cheap catalytic materials thus allowing to match or to outperform noble-metal-based catalysts.…”

Co-generation of hydrogen and power/current pulses from supercapacitive MFCs using novel HER iron-based catalysts

“…Fe-N-C catalysts have been extensively studied for oxygen reduction reaction (ORR) in acidic [28], [29], [30], [31], neutral [32], [33], [34], [35] and alkaline conditions [36], [37], [38], [39]. The materials were found to be extremely active in all pH conditions and performance was better than Pt in alkaline media [40].…”