Modeling Fe/N/C Catalysts in Monolayer Graphene

Abstract

Pyrolyzed Fe/N/C is one of the most promising non-precious-metal catalysts for the oxygen reduction reaction (ORR), which is supposed to boost the commercialization of proton exchange membrane fuel cells (PEMFC). However, the nature of the active sites of Fe/N/C is not clear and has long been debated. The challenges mainly come from highly heterogeneous structures formed during the pyrolysis process as well as no suitable surface probes. To elucidate the active sites, the most effective approach is building well-defined model catalysts as single-crystal planes in surface sciences. Herein, we designed a single-atomic-layer Fe/ N/C model catalyst based on monolayer graphene (FeN-MLG) to explore the active sites. The model catalyst was prepared by 950 °C heat treatment of graphene with controlled defects under an FeCl 3 (g)/NH 3 atmosphere. The as-prepared model catalyst exhibits ORR activity and SCN − suppressive effect comparable to those of normal nanoparticle-like Fe/N/C catalysts, indicating that active sites are successfully created in the model catalyst. The effect of defect density, the layer number of graphene, and nitrogen species on the ORR activity has been investigated. The main content of nitrogen species on FeN-MLG is N x -Fe, and quantitative correlation between N x -Fe and ORR activity demonstrates that N x -Fe species are the active site of Fe/N/C catalysts. The proposed model catalyst serves to simplify the catalyst structures and to simulate the topmost atomic layer of normal Fe/N/C, where ORR is catalyzed. This model system opens an opportunity to further understand the highly heterogeneous Fe/N/C catalysts.

Preparation of Iron‐ and Nitrogen‐Codoped Carbon Nanotubes from Waste Plastics Pyrolysis for the Oxygen Reduction Reaction

“…[11] Among the different M-N-C catalysts, Fe-N-Cc atalysts have been studied extensively because of their excellent catalytic activity. [12] Both theoreticalc alculations [13] and experiments [14] have revealed that nitrogen incorporation and Fe-coordinated carbon speciesa re responsible for great improvements in the ORR activity.N evertheless, to date, most Fe-N-C catalysts still suffer from unsatisfactory stability or durability in harsh electrolyte solutionso wing to the instability of iron. [15] More importantly, complicated fabrication processes and expensive chemical reagents also restrict scalablep roduction.…”

Importance of Electrocatalyst Morphology for the Oxygen Reduction Reaction

“…Generally, the enhanced ORR performance is mainly related with the M‐N x species and N doping structure. Fe−N 4 and Co−N 4 species of M−N−C structures derived from the metal doping or direct pyrolysis are highly active species for ORR ,,. Furthermore, the ORR performance will be further enhanced when NPs such as Fe, Co, Cu, and Fe 3 C, were encapsulated inside the carbon shell.…”

“…FeÀ N 4 and CoÀ N 4 species of MÀ NÀ C structures derived from the metal [207] doping or direct pyrolysis are highly active species for ORR. [106,211,212] Furthermore, the ORR performance will be further enhanced when NPs such as Fe, Co, Cu, and Fe 3 C, were encapsulated inside the carbon shell. The Fe@C NPs can enhance the ORR performance of neighboring FeÀ N x species.…”

V4P6.98/VO(PO3)2 as an Efficient Non‐Noble Metal Catalyst for Electrochemical Hydrogen Evolution in Alkaline Electrolyte

“…Herein, we synthesized a flower-like V 4 P 6.98 /VO(PO 3 ) 2 catalyst on a nickel foam substrate as an efficient non-noble metal catalyst for electrochemical hydrogen evolution in alkaline electrolyte. Thus, it remains challenging to develop non-noble metal HER catalysts with a high activity for water splitting in alkaline media.Non-noble metal catalysts based on Co, [4][5][6][7][8] Ni, [9][10][11][12][13][14] Fe, [15][16][17] and Mo [5,[18][19][20] have been intensively used as HER catalysts owing to the high abundance of these elements and the their low cost, and high catalytic activities. We report a low-cost and high-efficiency non-noble metal HER catalyst beyond the commonly used transition metals (Ni, Co, Mo, Cu, and Fe), which expands the scope of non-noble-metal phosphide catalysts for water splitting.…”

“…Non-noble metal catalysts based on Co, [4][5][6][7][8] Ni, [9][10][11][12][13][14] Fe, [15][16][17] and Mo [5,[18][19][20] have been intensively used as HER catalysts owing to the high abundance of these elements and the their low cost, and high catalytic activities. In the past few years, V-based oxides, sulfides, and nitrides show promise for applications in the field of energy conversion and storage, such as supercapacitors and rechargeable batteries for their high-electrochemical performance and earth abundance.…”