Fe atoms anchored on defective nitrogen doped hollow carbon spheres as efficient electrocatalysts for oxygen reduction reaction

Abstract

Defective electrocatalysts, especially for intrinsic defective carbon, have aroused a wide concern owing to high spin and charge densities. However, the designated nitrogen species favorable for creating defects by the removal of nitrogen, and the influence of defects for the coordination structure of active site and oxygen reduction reaction (ORR) activity have not been elucidated. Herein, we designed and synthesized a pair of electrocatalysts, denoted as Fe-N/C and Fe-ND/C for coordination sites of atomic iron-nitrogen and iron-nitrogen/defect configuration embedded in hollow carbon spheres, respectively, through direct pyrolysis of their corresponding hollow carbon spheres adsorbed with Fe(acac)3. The nitrogen defects were fabricated via the evaporation of pyrrolic-N on nitrogen doped hollow carbon spheres. Results of comparative experiments between Fe-N/C and Fe-ND/C reveal that Fe-ND/C shows superior ORR activity with an onset potential of 30 mV higher than that of Fe-N/C. Fe-ND sites are more favorable for the enhancement of ORR activity. Density functional theory (DFT) calculation demonstrates that Fe-ND/C with proposed coordination structure of FeN4−x (0<x<4) anchored by OH as axial ligand during ORR, weakens the strong binding of OH* intermediate and promotes the desorption of OH* as rate-determining step for ORR in alkaline electrolyte. Thus, Fe-ND/C electrocatalysts present much better ORR activity compared with that of Fe-N/C with proposed coordination structure of FeN4.

Structural revolution of atomically dispersed Mn sites dictates oxygen reduction performance

“…On the basis of LSV plots at various rotating rates and corresponding Koutecky−Levich (K-L) plots (Fig. S21 in the ESM), the transferred electron number was revealed to be 3.97 for Mn SAs-N 4 , delivering a preferred 4-electron pathway [36,37]. The H 2 O 2 yield of Mn SAs-N 4 catalyst is less than 3% over the measured potential range (Fig.…”

Synthesis of Tangled Iron‐Nitrogen Co‐doped Carbon Nanosheets through a Dopamine Coordination Strategy for the Oxygen Reduction Reaction

“…The characteristics of D band at ~1338 cm À 1 and G band at ~1591 cm À 1 in Raman spectra represent the carbon lattice defects and sp 2 -hybridized carbon atoms, respectively. [33,34] The relative intensity ratio of I D /I G of FeÀ NÀ C/ 700 (Figure 2b and S3b) is higher than that of FeÀ NÀ C/700-Pre, implying the secondary pyrolysis yields lower crystallinity and more defects in the carbon substrate. [35] Such phenomenon was highly consistent with the above XRD results.…”

“…To further illustrate the graphitic degree and structural defects of carbon substrate, Raman spectra were performed. The characteristics of D band at ∼1338 cm −1 and G band at ∼1591 cm −1 in Raman spectra represent the carbon lattice defects and sp 2 ‐hybridized carbon atoms, respectively [33,34] . The relative intensity ratio of I D /I G of Fe−N−C/700 (Figure 2b and S3b) is higher than that of Fe−N−C/700‐Pre, implying the secondary pyrolysis yields lower crystallinity and more defects in the carbon substrate [35] .…”

Hollow microstructural regulation of single-atom catalysts for optimized electrocatalytic performance

“…Furthermore, they emphasize the accessibility of SACs with high activity and the synergistic interaction of Co-Ni-N in reducing the energy barrier and improving the reaction kinetics. Deng et al [108] used a hollow ZIF-8 precursor to prepare N-doped hollow carbon polyhedra implanted with single Fe atoms (C-FeHZ 8 @g-C 3 N 4 ). The obtained FeHZ 8 @g-C 3 N 4 catalysts possessed an exclusively high density of Fe-N 4 sites and exhibited excellent ORR activity with a half-wave potential of 0.78 V in an acidic medium and 0.845 V in an alkaline medium.…”