Journal Report Du Qian

Structural Selectivity of CO Oxidation on Fe/N/C Catalysts P. Zhang, X. F. Chen, J. S. Lian, and Q. Jiang J. Phys. Chem. C 2012, 116, 17572−17579

We have performed extensive density functional theory calculations for the elementary steps in CO oxidation on Fe/N/C active sites, including Fe-N4 and Fe-N3 porphyrin-like carbon nanotube (T-FeN4 and T-FeN3), Fe-N4 porphyrin-like graphene (G-FeN4), and Fe-N2 nanoribbon (R-FeN2).

E ad values of O 2 are larger than that of CO on T-FeN3 and R-FeN2, suggesting that Fe in TFeN3 and R-FeN2 will be dominantly covered by the adsorbed O 2 if the CO/O 2 mixture is injected as the reaction gas. However, CO adsorption is more favorable than O 2 on T-FeN4 and G-FeN4

TFeN3: Not only O 2 -2π*, but also O 2 -1π, O 2 -5σ, and O 2 -4σ*, interact with Fe-3d T-FeN4 and G-FeN4 :The dominating contributions for O 2 adsorption are the interactions between O 2 -2π* and Fe-3d orbitals. The CO interact with Fe chiefly through hybridization between CO-5σ and Fe-3d, also CO-2π* and Fe-3d. Since the E ad value of CO on Fe/N/C is not only related to the electron donation from CO-5σ to metals but also to electron back- donation from metals to CO-2π*

T-FeN4 and G-FeN4 （ a ） CO + O 2 → OOCO → CO 2 + O （ RDS ） (b) CO + O → CO 2 The electron transfer within the tube walls is easier on the T-FeN4 than on the G- FeN4 due to the larger curvature of the former.

T-FeN3 First, 3 CO molecules can adsorb on Fe in T-FeN3, 2 CO 2 were produced. Both of CO and O2 can be readily coadsorbed on the embedded-Fe atom O 2 first dissociates rather than reacts with CO to form O−O−CO(a). CO oxidation(b)

R-FeN2 O2 first is adsorbed on Fe instead of reacting with two CO to form COOOOC complex

3D Nitrogen-Doped Graphene Aerogel-Supported Fe 3 O 4 Nanoparticles as Efficient Electrocatalysts for the Oxygen Reduction Zhong-Shuai Wu, Shubin Yang, Yi Sun, Khaled Parvez, Xinliang Feng and Klaus Müllen J. Am. Chem. Soc. 2012, 134, 9082−9085

C atalysts for the oxygen reduction reaction (ORR) are keycomponents of fuel cells. Metals (Fe, Co, etc.) or metal oxides (Fe 2 O 3, Fe 3 O 4, Co 3 O 4, IrO 2, etc.) as well as nitrogencoordinated metal on carbon4 and metal-free doped carbon materials have been actively pursued. I n this communication, we demonstrate Fe3O4/N-GAs, a novel class of monolithic Fe 3 O 4 NPs supported on 3D N-doped graphene aerogels (N- GAs).

Fabrication process 1. Graphene oxide (GO ） was dispersed in water by sonication, reaching a concentration up to 1.5 mg mL −1. 2. Iron acetate (1−40 mg) and polypyrrole (PPy) (20 mg) were slowly added to 6 mL of the GO dispersion to form a stable aqueous suspension. 3.Ternary components were hydrothermally assembled at 180 °C for 12 h to form a graphene-based 3D hydrogel. 4. The as-prepared hydrogel was directly dehydrated via a freeze-drying process to maintain the 3D monolithic architecture and then heated at 600 °C for 3 h under nitrogen. Figure1

Result and discussion （ a ） The XRD no apparent diffraction peak could be identified at 20−30°, indicating that Fe 3 O 4 NPs were efficiently deposited on the graphene surface, suppressing the stacking of graphene layers. (b−d) Typical SEM images of Fe 3 O 4 /N-GAs. (e) TEM and (f) HRTEM images of Fe 3 O 4 /N-GAs (with sizes of 20−80 nm) revealing an Fe 3 O 4 NP wrapped by graphene layers. Figure2

(a)Typical STEM image. (b) STEM image taken from the square region marked in (a) (c-f ） Corresponding elemental mapping images of (c) Fe, (d) C, (e) N, and (f) O. (g, h) High-resolution XPSspectra of Fe 3 O 4 /N- Gas (g) Fe 2p; (h) N 1s I t is notable that the nitrogen content is much higher in the region of Fe 3 O 4 NPs than in graphene layers (Figure 3e), indicating that Fe−N−C active sites have been established at the Fe 3 O 4 NP interface. T he high-resolution N 1s scan, (Figure 3h) indicated the presence of two forms of nitrogen, namely, pyrrolic N (401.0±0.2 eV) and pyridinic N (398.1±0.2eV) Figure3

Figure4 (a) RRDE test of the ORR on Fe 3 O 4 /N-GAs, Fe 3 O 4 /N-GSs( graphene sheets), Fe 3 O 4 /N-CB (carbon black), both Fe3O4/N-GSs and Fe 3 O 4 /N-CB exhibited much higher ring currents than Fe 3 O 4 /N-Gas (b) H 2 O 2 yield (c) electron transfer number of Fe 3 O 4 /N-GAs, Fe 3 O 4 /N-GSs, and Fe 3 O 4 /N-CB, n=3.72−3.95 for Fe 3 O 4 /N-GAs electrode over the whole potential range, emphasizing that the Fe 3 O 4 /N-GAs ORR proceeds mainly via a four-electron mechanism. (d) Peroxide percentage and electron transfer number as functions of Fe3O4 loading