Thermally Controlled Construction of Fe–N_x Active Sites on the Edge of a Graphene Nanoribbon for an Electrocatalytic Oxygen Reduction Reaction

Abstract

Pyrolytically prepared iron and nitrogen codoped carbon (Fe/N/C) catalysts are promising nonprecious metal electrocatalysts for the oxygen reduction reaction (ORR) in fuel cell applications. Fabrication of the Fe/N/C catalysts with Fe−N x active sites having precise structures is now required. We developed a strategy for thermally controlled construction of the Fe−N x structure in Fe/N/C catalysts by applying a bottom-up synthetic methodology based on a N-doped graphene nanoribbon (N-GNR). The preorganized aromatic rings within the precursors assist graphitization during generation of the N-GNR structure with ironcoordinating sites. The Fe/N/C catalyst prepared from the N-GNR precursor, iron ion, and the carbon support Vulcan XC-72R provides a high onset potential of 0.88 V (vs reversible hydrogen electrode (RHE)) and promotes efficient four-electron ORR. X-ray absorption fine structure (XAFS) and X-ray photoelectron spectroscopy (XPS) studies reveal that the N-GNR precursor induces the formation of iron-coordinating nitrogen species during pyrolysis. The details of the graphitization process of the precursor were further investigated by analyzing the precursors pyrolyzed at various temperatures using MgO particles as a sacrificial template, with the results indicating that the graphitized structure was obtained at 700 °C. The preorganized N-GNR precursors and its pyrolysis conditions for graphitization are found to be important factors for generation of the Fe−N x active sites along with the N-GNR structure in high-performance Fe/N/C catalysts for the ORR.

Formation of Tilted FeN4 Configuration as the Origin of Oxygen Reduction Reaction Activity Enhancement on a Pyrolyzed Fe-N-C Catalyst with FeN4-Edge Active Sites

“…The rate of coverage change constitutes the coupled differential equations. The rate of change is defined as (10) θ i is the fractional coverage of species i, n j is the number of adsorbate i being consumed (−) or produced (+) in step-j, and r j is the step-j where species i is involved. The set of coupled differential equations was computed numerically until a steady state is reached.…”

“…In recent years, various methods have been proposed to engineer the active site structures and to enhance the ORR activity of pyrolyzed Fe-N-C catalysts . Among them is by dispersing the FeN 4 active site near the graphitic edges (FeN 4 -edge) of the catalyst. − In 2020, Ma et al reported a combined experimental and theoretical study discussing the ORR activity of a pyrolyzed Fe-N-C catalyst with abundant graphitic edges . This catalyst is reported to have excellent ORR activity and durability, rivaling that of the Pt/C catalyst.…”

Porous FeP supported on 3D nitrogen-doped carbon fibers as efficient electrocatalysts for wide-pH hydrogen evolution

“…[29][30][31] XPS analysis shows the existence of Fe-N in p-FeP/NCF/CP, which may also contribute and facilitate the activity of the catalyst. 26,[32][33][34][35][36] Therefore, the 3D network and porous structure of p-FeP/NCF/CP endows its advantages of exposing more active sites for HER, and the low crystallinity and the existence of Fe-N collectively account for its high catalytic activity toward HER.…”

Diels–Alder Cycloaddition with CO, CO2, SO2, or N2 Extrusion: A Powerful Tool for Material Chemistry

“…The application possibilities listed above have been discussed in this review. Particular attention is paid to nanographenes, including functionalized and heteroatoms-doped ones, which preparation and new applications constitute a “hot topic” in science and technology [ 6 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 ]. Currently, only bottom-up methods, where nanographene is constructed from smaller entities by stepwise organic synthesis, allow the preparation of nanographenes, including functionalized and doped ones, with perfect control of shapes and sizes and, therefore, perfectly defined properties [ 2 , 5 , 6 , 11 , 12 ,…”

“…It should be added that nanographenes (graphenoids), obtained via reactions discussed in this review, can be planar or otherwise distorted, that is, non-planar, one- (1D), two- (2D), and three-dimensional (3D) [ 6 , 11 , 12 , 17 , 23 , 24 , 25 , 26 , 36 , 38 , 40 , 43 , 46 , 47 , 49 , 52 ]. Graphenoids with planar sheets of varying size, shape, and periphery have made great progress in practical applications of electronics, energy storage, catalysis, and biosensing [ 6 , 11 , 12 , 14 , 15 , 16 , 17 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 42 , 44 , 47 , 50 , 52 , 53 ]. In recent years, a growing number of graphenoid studies have focused on unusual curved and warped stru...…”