Effect of pyrolysis pressure on activity of Fe–N–C catalysts for oxygen reduction

Abstract

Iron and nitrogen doped carbon, Fe-N-C, catalysts are synthesized by high pressure pyrolysis of Ketjenblack carbon, melamine and iron acetate precursor mixture in a closed, reusable scale-up stainless steel reactor. The effects of precursor loading with constant precursor ratios on obtained pressure, nitrogen retention and oxygen reduction reaction (ORR) activities are studied. The results indicate that higher precursor loading increases the gas phase pressure and improves nitrogen retention and ORR activity. Furthermore, a relationship is found between active site density, nitrogen retention and pressure that suggests that the limiting reaction may be an adsorption process driven via high pressure of volatile intermediates from the melamine. Figure 7. a) Fuel cell polarization curves of Fe-N-C samples obtained in a single cell (5 cm 2 ) on air with 2.5 bar back pressure. The loadings are 2.4-3.2 mg cm -2 and normalized to 3 mg cm -2 and b) fuel cell polarization curves of 3.5 g Batch with 2.5 back pressure in air and 0.5 bar backpressure in O2. The loadings are 3 mg cm -2 .Polarization curves were obtained at 100% RH using 211 Nafion®, 55 wt% 1100 EW and 25BC GDL.

Enhanced Oxygen Reduction Stability and Activity by Co and N (or O) Interaction in CoO on N‐Doped Carbon Prepared through Spray Pyrolysis

“…Notably, the pyridinic and graphitic nitrogen, considered to be the most efficient active sites of all the nitrogen species in CoO/NC are able to not only enhance the initial chemical adsorption of oxygen on the catalyst surface but increase the number of catalytically active sites for ORR . Moreover, the interaction between Co and N in the Co−N bonds (399.1 eV) increases active sites and improves the ORR performance due to the electron density redistribution . Accordingly, the total amount of N in CoO/NC2 was estimated to be 2.56 at.% by XPS analysis.…”

“…As shown in Figure 1, XRD analysis confirmed the crystallographic structure of the specimens prepared using the spray pyrolysis process. It was observed that Ketjenblack has a relatively broad peak near 268 for a graphitic carbon plane (002) without sharp peaks for different elements, [29][30][31] . This means that the cobalt nitrate used as the precursor was completely decomposed and oxidized to cobalt(II) oxide during spray pyrolysis at a reaction temperature of 600 8C and a short residence time (< 4 s).…”

“…[44] Moreover, the interaction between Co and N in the CoÀN bonds (399.1 eV) increases active sites and improves the ORR performance due to the electron density redistribution. [27][28][29][30][31] Accordingly, the total amount of N in CoO/NC2 was estimated to be 2.56 at.% by XPS analysis. These XPS results clearly verified the formation of the CoÀNÀC and CoÀOÀC bonds in the CoO/NC2.…”

Composite Electrocatalyst Derived from Hybrid Nitrogen‐Containing Metal Organic Frameworks and g‐C3N4 Encapsulated In Situ into Porous Carbon Aerogels

“…At present, one of the effective methods is to regulate the specific surface area and pore size of the catalyst and thus expose more active sites . Some researchers use porous carbon support materials such as carbon aerogel (CA) or graphene foam and further control their morphology for this purpose . In some studies, a template method is used to increase the specific surface area of carbon supports .…”

“…[19][20][21] Some researchers use porous carbon support materials such as carbon aerogel (CA) or graphene foam and further control their morphology for this purpose. [22][23][24] In some studies, a template method is used to increase the specific surface area of carbon supports. [25][26][27] Recently, metal organic frameworks (MOFs), as developing kinds of periodic porous three-dimensional framework polymers, have also been widely used in ORR catalysts.…”