Architecting FeN_x on High Graphitization Carbon for High‐Performance Oxygen Reduction by Regulating d‐Band Center

Abstract

Fe single atoms and N co‐doped carbon nanomaterials (Fe‐N‐C) are the most promising oxygen reduction reaction (ORR) catalysts to replace platinum group metals. However, high‐activity Fe single‐atom catalysts suffer from poor stability owing to the low graphitization degree. Here, an effective phase‐transition strategy is reported to enhance the stability of Fe‐N‐C catalysts by inducing increased degree of graphitization and incorporation of Fe nanoparticles encapsulated by graphitic carbon layer without sacrificing activity. Remarkably, the resulted Fe@Fe‐N‐C catalysts achieved excellent ORR activity (E1/2 = 0.829 V) and stability (19 mV loss after 30K cycles) in acid media. Density functional theory (DFT) calculations agree with experimental phenomena that additional Fe nanoparticles not only favor to the activation of O2 by tailoring d‐band center position but also inhibit the demetallization of Fe active center from FeN4 sites. This work provides a new insight into the rational design of highly efficient and durable Fe‐N‐C catalysts for ORR.

Single-Atom-Based Oxygen Reduction Reaction Catalysts for Proton Exchange Membrane Fuel Cells: Progress and Perspective

“…The theoretical calculations and experimental results unveiled that the durability is due to Mn doping into the zinc-containing zeolitic imidazolate framework (ZIF-8) precursors promoting an extent of graphitization and enhanced corrosion resistance of adjacent carbon of MnN 4 sites. Lately, Li and co-workers reported a hierarchically porous Fe@Fe–N–C catalyst that consisted of graphitic carbon enwrapped Fe NPs supported on Fe–N–C with excellent long-term stability (19 mV loss after 30000 cycles) in acidic media, which indicated that the enhanced graphitization degree of the carbon substrate could contribute to increasing the electron conductibility and anticorrosion capability for stable Fe–N–C SACs . However, it is essential to note that the graphitization treatment may cause a massive decrease in the mass of microspore-hosted MN x moieties due to insufficient defects and N dopants, which further degrades the ORR activity.…”

Spontaneous Internal Electric Field in Heterojunction Boosts Bifunctional Oxygen Electrocatalysts for Zinc–Air Batteries: Theory, Experiment, and Application

“…The Fe x N@PC-based ZAB delivers a high opencircuit voltage (OCV) of 1.504 V as shown in Figure 6a, while the Pt/C+RuO 2 -based ZAB has an OCV of 1.385 V (Figure S18, Supporting Information), indicating the efficient electrocatalytic activity of Fe x N@PC. The discharge polarization and corresponding power density curves (Figure 6b) reveal that Fe x N@PC-based ZABs achieve a super-high power density of 223.67 mW cm −2 at 397.03 mA cm −2 (beyond the state-of-the-art, Table S3, Supporting Information), [9,[67][68][69][70][71][72][73][74][75][76][77][78][79] which is higher than that of Pt/C+RuO 2 (130.42 mW cm −2 at 187.65 mA cm −2 ). In the V-t curves of Figure 6c, the Fe x N@PC-based ZAB remains at a higher OCV of 1.44 V after 400 s, which is also higher than that of Pt/C+RuO 2 (1.37 V).…”

Synergy Between Supported Metal Single Atoms and Nanoparticles and their Relevance in Catalysis

“…To understand the role that Fe NP play in the experimentally evidenced superior ORR activity of Fe SA+NP /N−C catalysts, DFT calculations are usually performed. The wide variety of models used, including Fe NP on the support or on the Fe SA , surely explains the differences in the levels of rationalization proposed from one study to another [29b,30–32] . According to the experimental results, the ORR proceeds via a four‐electron pathway through O 2 *, HOO*, O*, and HO* key intermediates.…”

“…This is generally accompanied by an increase of the Bader charge on the metal SA [32b,33] . Increasing ORR activity was thus correlated to a decrease of the adsorption energy of one OH* intermediate, [29b,31,32b,d,34] or modification of energy barriers for OOH* formation or dissociation [32a] . Fe NP were also proposed to increase the local charge density of FeN 4 , subsequently enhancing O 2 adsorption/activation, resulting in the facile cleavage of the O−O bond [30,32c] .…”