Impact of Surface Functionalization on the Intrinsic Properties of the Resulting Fe–N–C Catalysts for Fuel Cell Applications

Abstract

Herein, Fe–N–C catalysts are prepared from surface functionalized carbon nanotubes (CNTs) in combination with iron acetate and phenanthroline. An improved performance and structural composition is obtained by surface functionalization of the CNTs with indazole or pyridine. Catalyst composition and morphology are characterized by transmission electron microscopy, N2 sorption, photoelectron spectroscopy, and 57Fe transmission Mössbauer spectroscopy. However, activity and selectivity toward oxygen reduction reaction are determined from rotating ring disc electrode (RRDE) experiments. The durability and stability are evaluated by accelerated stress tests (0.0–1.2 V) and differential electrochemical mass spectroscopy (DEMS), respectively. It is shown that surface functionalization with indazole enables the direct attachment of FeN4 centers to CNTs so that no impurity species are detected and a high activity is achieved, that can be attributed to an improved turnover frequency and higher mass‐based site density. Even more striking is the excellent durability and stability of the realized catalyst. While these trends are well pronounced in RRDE and DEMS, challenges in the preparation of membrane electrode assemblies make the trend not as obvious in fuel cells (FCs).

Incorporation of Activated Biomasses in Fe-N-C Catalysts for Oxygen Reduction Reaction with Enhanced Stability in Acidic Media

“…After the AST for all catalysts, an increase in capacity due to the formation of surface functional oxygen groups or pores is observed, indicating oxidation of the carbon surface (eq ). This is further evidenced by the appearance of a broad hydroquinone/quinone redox couple with a peak maximum at around 0.7 V for all catalysts . These results are in accordance with the comparable changes in Tafel slopes (Figure and Table ), which also shows oxygenation of the catalyst’s surface.…”

Impact of Pore Structure on Two‐Electron Oxygen Reduction Reaction in Nitrogen‐Doped Carbon Materials: Rotating Ring‐Disk Electrode vs. Flow Cell

“…Under the RRDE test conditions, the mass transfer effect is minimized, the ORR selectivity is mainly determined by the intrinsic catalytic sites. [24] The observed similar ORR selectivity indicates the similarity of catalytic sites of the eight N/C-x% CO 2 catalysts. Moreover, we tried to correlate the ORR activity or selectivity with several different N species in the RRDE test (Figures S5 and S6).…”

Structural Evolution of Atomically Dispersed Fe Species in Fe–N/C Catalysts Probed by X-ray Absorption and 57Fe Mössbauer Spectroscopies

“…The doublet D1 represents Fe 2+ coordinated by four pyrrolic N groups connected to a carbon support, and it is assigned to low-spin Fe 2+ –N 4 . The doublets D2 and D3 consist of ferrous intermediate-spin sites, and the main difference between the two doublets is their Fe local environments. ,,,,,− The δ iso and Δ E Q values of D2 are close to those of FePc, while the values of D3 are similar to those of Fe porphyrins. , The singlet (Sing) represents superparamagnetic Fe, which has a smaller size than the Weiss domain; thus, it does not have a magnetic splitting value ( H 0 ).…”