Nitrogen-doped carbons catalysts

Another gemstone in the portfolio of rational carbon synthesis is nitrogen-doped carbons. Recently, they became the subject of particular interest to researchers due to their remarkable performance in applications such as C02 sequestration [22], removals of contaminants from gas and liquid phases [23], environmental protection [24], catalysts and catalysts supports [25], or in electrochemistry as supercapacitors [26], cells and batteries to improve stability and the loading capacity of carbon. 

Chapter 6 provides an extensive review of the uses of carbon as a catalyst, with particnlar emphasis being placed on cases in which active sites have been properly identified and activity correlations established. The special case of nitrogen-doped carbons and their catalytic activity in oxidation reactions is discussed in Chapter 7, and Chapter 8 covers the heterogenization of homogeneous catalysts by anchoring transition-metal complexes onto the snrface of suitable carbon materials. 

Non platinum metal catalysts such as for example pyrolyzed complexes of cobalt or iron or other nitrogen doped carbon materials have also been investigated for the oxygen reduction reaction [51, 52], however have not found widespread use today. 

CoSe2 nanomaterials have also been prepared as catalysts for nitrogen doped carbons as low cost materials. The carbon supports were synthesised by pyrolysis of vulcan, which was coated with carbon and nitrogen precursors with formaldehyde and ethylene diamine or 1,6-diaminohexane being the carbon and nitrogen sources respectively. To load the CoSca layer dicobalt octacarbonyl and nitrogen doped carbon were mixed with 200 ml dehydrated jylene. The carbonyl sol was then refluxed for 2 h at 140 °C in a four neck flask with nitrogen protection. 

Nitrogen-doped carbon nanotubes as a cathode catalyst for the oxygen reduction reaction in alkaline medium. Electrochem. Commun., 12 (3), 338- 341. 

Besides the work of Ozkan and Popov s groups and the work of the Japanese consortium, other authors also defended the same view as Wiesener that of a CNx catalytic site for ORR. Their results will now be summarized. It should be stressed that among these authors, some have made a particular effort to avoid any metal trace in the synthesis of their catalysts in order to determine the true ORR activity of the nitrogen-doped carbon materials. Their results will be presented first, followed by the results of authors using either Fe- or Co-containing molecules in the synthesis of their N-doped carbon catalysts. 

Recently, the research on exploring the use of carbon nanomaterials as metal-free catalysts has been one of the major subjects for the fuel cell research. Owing to their wide availability, environmental acceptability, corrosion resistance, and unique surface and bulk properties, carbon nanomaterials are ideal candidates for metal-free ORR catalysts. In this context, we have demonstrated that vertically aligned nitrogen-doped carbon nanotube (VA-NCNTs) array exhibited three times higher ORR electrocatalytic activity and better long-term operation durability... 

However, beside the function as a catalyst support, it was reported that nitrogen-doped carbon itself can be active as a metal-free catalyst for the ORR. The nitrogen atoms will (1) change the electronic character of the carbon and (2) the obtained defect structure (in comparison to the inert surface of graphene sheets) might enable an easier adsorption of oxygen and a subsequent reduction to water or hydrogen peroxide. 

Reviews of the literature on the role of organometallic complexes in the synthesis of CNTs [8] and nitrogen-doped carbon nanotubes (NCNTs) [6] have been written. However, to date, little has been discussed about the role of these catalysts in affecting the shape of the carbons produced. 

Nitrogen-doped carbon materials shows good catalysts support in terms of catalytic activity and stability [18,19]. A graphitic carbon nitride with three-dimensionally extended highly ordered pore arrays has been reported as a support for a Pt-Ru alloy catalyst of a DMFC anode. The nanostructured C3N4 has 73-83% higher power density than Vulcan XC-72, a commercial carbon black. 

Nitrogen-doped carbon nanotubes as platinum catalyst supports for oxygen reduction reaction in proton exchange membrane fuel cells. The Journal of Physical Chemistry C, 114 (50), 21982-21988. 

Nitrogen-Doped Carbon Composites as Metal-Free Catalysts... 

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