Phenylenediamine-Based FeN_x/C Catalyst with High Activity for Oxygen Reduction in Acid Medium and Its Active-Site Probing

Abstract

High-temperature pyrolyzed FeN(x)/C catalyst is one of the most promising nonprecious metal electrocatalysts for oxygen reduction reaction (ORR). However, it suffers from two challenging problems: insufficient ORR activity and unclear active site structure. Herein, we report a FeN(x)/C catalyst derived from poly-m-phenylenediamine (PmPDA-FeN(x)/C) that possesses high ORR activity (11.5 A g(-1) at 0.80 V vs RHE) and low H2O2 yield (<1%) in acid medium. The PmPDA-FeN(x)/C also exhibits high catalytic activity for both reduction and oxidation of H2O2. We further find that the ORR activity of PmPDA-FeN(x)/C is not sensitive to CO and NO(x) but can be suppressed significantly by halide ions (e.g., Cl(-), F(-), and Br(-)) and low valence state sulfur-containing species (e.g., SCN(-), SO2, and H2S). This result reveals that the active sites of the FeN(x)/C catalyst contains Fe element (mainly as Fe(III) at high potentials) in acid medium.

Graphene-templated synthesis of sandwich-like porous carbon nanosheets for efficient oxygen reduction reaction in both alkaline and acidic media

“…The high-resolution N 1s spectrum (Fig. S4b) can be deconvoluted into several peaks at 398.5, 399.5, 400.3, 401.3, and 403.9 eV, which can be assigned to pyridinic N (24.3%), Fe-N (4.6%), terminal graphitic N (10.3%), central graphitic N (54.1%) and oxidized N (6.7%), respectively [28]. The high content of pyridinic and graphitic N which are also identified in the X-ray near-edge structure spectrum of N K-edge (XANES, Fig.…”

“…3d) can be divided into three peaks for FeN x (711.1 eV), FeS (724.03 eV), and Fe (708.1 eV) with a satellite peak at 716.8 eV [53]. The peak at 711.1 eV suggested the existence of Fe-N species which are active sites for ORR [28,62].…”

“…SCN í ions are known to strongly coordinate with metal ions to form stable complexes and hence poison the metal containing active sites in acidic conditions [28]. As shown in Fig.…”

“…In particular, Fe/Ndoped carbon electrocatalysts have been considered as a very promising family of NPMCs for ORR because of the high catalytic activity, easy access, and cheap iron resources [24][25][26][27][28][29][30][31][32]. However, the ORR activity of Fe-N-C catalysts still remains deficient compared to that of Ptbased catalysts in acidic media, owing to the low density of active sites [33][34][35][36][37][38].…”

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“…f Effects of SCN − ions (5 mM) on ORR activity of Fe/N/C catalyst in 0.1 M H 2 SO 4 . [107] b). As seen in Fig.…”