Characterization of the Iron Phase in CN_x-Based Oxygen Reduction Reaction Catalysts

Abstract

Catalysts for the oxygen reduction reaction were prepared from the pyrolysis of acetonitrile at 900 °C over iron particles on various supports. The iron phases present in the active materials were characterized by XRD, TEM, and Mössbauer spectroscopy. Typically, the iron particles were encased in carbon after pyrolysis, explaining how they could survive subsequent acid washes. The Fe phases present included metallic gamma iron, cementite, and two oxidized phases. Although the relative abundance of the phases varied with different supports, with treatment time, and after washing, there was no apparent correlation between the presence or abundance of a phase and activity. The phases present are consistent with Fe particles used to catalyze the formation of carbon fibers by catalytic chemical vapor deposition. After being washed with acid, there was no evidence for the presence of nitrogen-stabilized Fe sites on the carbon surface. These results support the hypothesis that Fe catalyzes the formation of ORR-active carbon nanostructures during pyrolysis at 900 °C in a carbon and nitrogen atmosphere and is not part of an active site itself.

Supercapacitor modified with methylene blue as redox active electrolyte

“…These metallic particles are predominantly located at the base of the nanotubes, on its tip or encased inside them and entrapped within the graphene layers or covered by thin layers of amorphous carbon. They may exhibit electrocatalytic effects 29 and redox activity or even dissolve and show electrochemical activity in solution 30 depending on the supporting electrolyte composition, as was demonstrated by J. L. Lyon el at 31 . The electrodic process observed occurs at the potential expected for the Fe 3+ /Fe 2+ reaction in sulfuric acid 32 .…”

Nitrogen-doped carbon xerogel: A novel carbon-based electrocatalyst for oxygen reduction reaction in proton exchange membrane (PEM) fuel cells

“…5b could be assigned to pyridinic-N, quaternary-N and pyridinic-N + -O À , respectively. 28,35,38,56 As shown in Fig. 5c, the C1s peak of N-CX sample becomes wider than that of CX sample.…”

“…[10][11][12][13][14] In order to decrease the cost of electrocatalysts and eliminate their dependence on noble metals, various non-noble metal catalysts have been explored recently as alternatives to the Pt-based electrocatalysts, which include chalcogenide catalysts, [15][16][17][18][19] transition metal macrocyclic compounds, [20][21][22] transition metallic oxides [23][24][25][26][27] and carbon-based catalysts. [28][29][30][31][32][33][34][35] In particular, carbon-based catalysts doped with the heteroatoms such as nitrogen (N) or boron (B) have been paid much attention and been proposed as typical non-noble metal catalysts for ORR [36][37][38] in alkaline media. Especially, since Gong et al 37 reported the superior activity and stability of nitrogen doped carbon nanotube in alkaline solution, the heteroatom doped carbon materials have been expected to be promising alternative Pt-based catalysts.…”

Tuning the catalytic property of nitrogen-doped graphene for cathode oxygen reduction reaction

“…Besides, heat-treated metal (Fe or Co)-N/C systems as another kind of non-Pt cathode catalyst have been under development for several decades [13][14][15], starting with the pioneer works by Jasinski [16] and by Yeager and co-workers [17]. Recently much progress has been made in this system [18][19][20][21].…”