Structural and surface characterization of ultrafine iron carbide particles generated by laser pyrolysis. I. High temperature He treatment

Sethuraman, Anantha R.; Stencel, J.M.; Rubel, Aurora M.; Cavin, Burl; Hubbard, Camden R.

doi:10.1116/1.579261

Cited by 22 publications

(9 citation statements)

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“…The peak at 712 eV was attributed to Fe(III) according to the value reported in the literature: 710.8-711.8 eV. 44,45 Dodelet et al and Gojkovic ´et al reported that the peak of Fe 2p 3/2 in heat-treated iron porphyrins adsorbed on carbon black shifted to a lower binding energy due to the formation of aggregates including Fe(0) (706.7-707.2 eV), [44][45][46] Fe(II) (707.1-708.7 eV), 44,45 or Fe carbides (706.7-706.9 eV) 46,47 with an increase in the heat-treatment temperature. [18][19][20]48 Gojkovic ´also reported a similar peak shift for Fe 2p 1/2 according to the binding energy: 49 Fe(III), 725.1 eV; Fe(II), 722.9 eV; Fe(0), 719.7 eV.…”

Section: Development Of Nanospace In Carbonized Materialsmentioning

confidence: 67%

Formation of Platinum-Free Fuel Cell Cathode Catalyst with Highly Developed Nanospace by Carbonizing Catalase

Maruyama

Abe

2005

Chem. Mater.

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The amount of platinum in the catalyst for the electrodes of polymer electrolyte fuel cells must be minimized to widely substitute this new energy system for conventional ones. In this study, a platinum-free catalyst for the cathodic oxygen reduction was formed from a natural organic compound, catalase. We carbonized catalase to produce a catalyst active in the superacidic atmosphere of the polymer electrolyte. Nitrogen adsorption onto the carbonized material revealed that the material had highly developed internal nanospaces, which were essential for exposing active sites to oxygen reduction on the pore surface. The carbonized material was also characterized by X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, and Mössbauer spectroscopy. The activity for oxygen reduction was evaluated using rotating disk electrodes, forming a catalyst layer from the carbonized material and the polymer electrolyte on the electrode surface and immersing the layer in oxygen-saturated perchloric acid. The activity increased with the increase in the specific surface area and possibly the increase in the activity of the respective active sites. A preliminary fuel cell test using the material in the cathode confirmed the electricity generation, although the performance was inferior to a Pt-based fuel cell.

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Section: Development Of Nanospace In Carbonized Materialsmentioning

confidence: 67%

Formation of Platinum-Free Fuel Cell Cathode Catalyst with Highly Developed Nanospace by Carbonizing Catalase

Maruyama

Abe

2005

Chem. Mater.

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“…A very weak peak at ∼405 eV also exists that is consistent with presence of “graphitic” quaternary nitrogen, corresponding to highly coordinated N atoms substituting inner carbon atoms within the graphene sheets . A very weak pair of doublets for the Fe2p 3/2 and Fe2p 1/2 signals at 707 and 720 eV and at 711 and 725 eV are seen, suggestive of the presence of metallic iron (or its carbide) and oxidized iron species. , Integration of the relative N and Fe elemental abundances indicates that CNFs contain ∼1% at. N and ∼0.1% at.…”

Section: Resultsmentioning

confidence: 82%

Direct Preparation of Carbon Nanofiber Electrodes via Pyrolysis of Iron(II) Phthalocyanine: Electrocatalytic Aspects for Oxygen Reduction

2004

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A facile method for the direct preparation of carbon nanofiber (CNF) electrodes by pyrolysis of iron(II) phthalocyanine on nickel substrates is reported. Uniform, large area coverage is observed with aligned bundles of CNFs exhibiting bamboo-like, hollow fibril morphology possessing diameters of 40-60 nm and lengths of ∼10 µm. The electrochemical behavior and stability of CNF electrodes as oxygen reduction catalysts were investigated by electrochemical methods. Without necessitation for extensive electrode pretreatment or surface activation, these electrodes demonstrate significant electrocatalytic activity in aqueous KNO 3 solutions at neutral to basic pH for the reduction of dioxygen to hydrogen peroxide, O 2 + H 2 O + 2eh HO 2 -+ OH -. As determined from chronocoulometry, slopes of Anson plots indicate that the overall electrochemical reaction proceeds by the peroxide pathway via two successive two-electron reductions. pH-dependent cyclic voltammetry studies indicate that the CNF electrodes are very active toward adsorption. At pH < 10 the one-electron reduction of O 2 to superoxide is rate limiting, whereas at more alkaline pH the reduction process is limited by the protonation of adsorbed superoxide. This is reflected by a change in measured apparent charge-transfer coefficient (R obs ) from R obs ) 0.5 to R obs ) 1 at neutral and high pH values, respectively. XPS, Raman, and TEM measurements suggest that the disorder in the graphite fibers and the presence of exposed edge plane defects and nitrogen functionalities are important factors for influencing adsorption of reactive intermediates and enhancing electrocatalysis for O 2 reduction.

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“…The broad nature of the 711 and 725 eV bands make it difficult to determine specifically which oxide form (e.g., hematite, ferrihydrite, etc.) is predominant in the nondoped CNFs . Still, it seems clear that the surface iron of nondoped CNFs is of a mixed valent nature while that of the N-doped CNFs consists of zerovalent (metallic) iron.…”

Section: Resultsmentioning

confidence: 96%

Influence of Nitrogen Doping on Oxygen Reduction Electrocatalysis at Carbon Nanofiber Electrodes

2005

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Nondoped and nitrogen-doped (N-doped) carbon nanofiber (CNF) electrodes were prepared via a floating catalyst chemical vapor deposition (CVD) method using precursors consisting of ferrocene and either xylene or pyridine to control the nitrogen content. Structural and compositional differences between the nondoped and N-doped varieties were assessed using TEM, BET, Raman, TGA, and XPS. Electrochemical methods were used to study the influence of nitrogen doping on the oxygen reduction reaction (ORR). The N-doped CNF electrodes demonstrate significant catalytic activity toward oxygen reduction in aqueous KNO(3) solutions at neutral to basic pH. Electrochemical data are presented which indicate that the ORR proceeds by the peroxide pathway via two successive two-electron reductions. However, for N-doped CNF electrodes, the reduction process can be treated as a catalytic regenerative process where the intermediate hydroperoxide (HO(2)(-)) is chemically decomposed to regenerate oxygen, 2HO(2)(-) <==> O(2) + 2OH(-). The proposed electrocatalysis mechanisms for ORR at both nondoped and N-doped varieties are supported by electrochemical simulations and by measured difference in hydroperoxide decomposition rate constants. Remarkably, approximately 100 fold enhancement for hydroperoxide decomposition is observed for N-doped CNFs, with rates comparable to the best known peroxide decomposition catalysts. Collectively the data indicate that exposed edge plane defects and nitrogen doping are important factors for influencing adsorption of reactive intermediates (i.e., superoxide, hydroperoxide) and for enhancing electrocatalysis for the ORR at nanostructured carbon electrodes.

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Structural and surface characterization of ultrafine iron carbide particles generated by laser pyrolysis. I. High temperature He treatment

Cited by 22 publications

References 0 publications

Formation of Platinum-Free Fuel Cell Cathode Catalyst with Highly Developed Nanospace by Carbonizing Catalase

Formation of Platinum-Free Fuel Cell Cathode Catalyst with Highly Developed Nanospace by Carbonizing Catalase

Direct Preparation of Carbon Nanofiber Electrodes via Pyrolysis of Iron(II) Phthalocyanine: Electrocatalytic Aspects for Oxygen Reduction

Influence of Nitrogen Doping on Oxygen Reduction Electrocatalysis at Carbon Nanofiber Electrodes

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