Nitrogen (N)-doped carbon materials exhibit high electrocatalytic activity for the oxygen reduction reaction (ORR), which is essential for several renewable energy systems. However, the ORR active site (or sites) is unclear, which retards further developments of high-performance catalysts. Here, we characterized the ORR active site by using newly designed graphite (highly oriented pyrolitic graphite) model catalysts with well-defined π conjugation and well-controlled doping of N species. The ORR active site is created by pyridinic N. Carbon dioxide adsorption experiments indicated that pyridinic N also creates Lewis basic sites. The specific activities per pyridinic N in the HOPG model catalysts are comparable with those of N-doped graphene powder catalysts. Thus, the ORR active sites in N-doped carbon materials are carbon atoms with Lewis basicity next to pyridinic N.

Active sites of nitrogen-doped carbon materials for oxygen reduction reaction clarified using model catalysts

Liming Dai,*,†,‡ Yuhua Xue,†,‡ Liangti Qu,* Hyun-Jung Choi, and Jong-Beom Baek* †Center of Advanced Science and Engineering for Carbon (Case4Carbon), Department of Macromolecular Science and Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106, United States Key Laboratory of Cluster Science, Ministry of Education of China, Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials, Department of Chemistry, School of Science, Beijing Institute of Technology, Beijing 100081, People’s Republic of China School of Energy and Chemical Engineering/Center for Dimension-Controllable Covalent Organic Frameworks, Ulsan National Institute of Science and Technology (UNIST), 100 Banyeon, Ulsan, 689-798, South Korea

Metal-free catalysts for oxygen reduction reaction.

Nitrogen-doped carbon nanofiber webs (CNFWs) with high surface areas are successfully prepared by carbonization-activation of polypyrrole nanofiber webs with KOH. The as-obtained CNFWs exhibit a superhigh reversible capacity of 943 mAh g(-1) at a current density of 2 A g(-1) even after 600 cycles, which is ascribed to the novel porous nanostructure and high-level nitrogen doping.

Nitrogen‐Doped Porous Carbon Nanofiber Webs as Anodes for Lithium Ion Batteries with a Superhigh Capacity and Rate Capability

Microporous activated carbon originating from coconut shell, as received or oxidized with nitric acid, is treated with melamine and urea and heated to 950 °C in an inert atmosphere to modify the carbon surface with nitrogen- and oxygen-containing groups for a systematic investigation of their combined effect on electrochemical performance in 1 M H2SO4 supercapacitors. The chemistry of the samples is characterized using elemental analysis, Boehm titration, potentiometric titration, and X-ray photoelectron spectroscopy. Sorption of nitrogen and carbon dioxide is used to determine the textural properties. The results show that the surface chemistry is affected by the type of nitrogen precursor and the specific groups present on the surface before the treatment leading to the incorporation of nitrogen. Analysis of the electrochemical behavior of urea- and melamine-treated samples reveal pseudocapacitance from both the oxygen and the nitrogen containing functional groups located in the pores larger than 10 A. On the other hand, pores between 5 A and 6 A are most effective in a double-layer formation, which correlates well with the size of hydrated ions. Although the quaternary and pyridinic-N-oxides nitrogen groups have enhancing effects on capacitance due to the positive charge, and thus an improved electron transfer at high current loads, the most important functional groups affecting energy storage performance are pyrrolic and pyridinic nitrogen along with quinone oxygen. (C)2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Combined Effect of Nitrogen- and Oxygen-Containing Functional Groups of Microporous Activated Carbon on its Electrochemical Performance in Supercapacitors

The characterization of activated carbons with oxygen and nitrogen surface groups

Evolution of nitrogen functionalities in carbonaceous materials during pyrolysis

NO and N2O decomposition over coal char at fluidized-bed combustion conditions

NO and N 2 O formation and destruction was studied in a laboratory-scale fluidized-bed combustor for a set of coals ranging from lignite to anthracite. For a given coal, the sum of fuel-N conversions to N 2 O and NO was found to be remarkably constant over a range of temperatures, although emission levels of individual species were strongly temperature-dependent (NO increases and N 2 O decreases with increasing temperature). A similar behavior was observed for the formation of NO and N 2 O during combustion of chars. This trade-off between N 2 O and NO emissions can be regarded as a constant conversion of fuel-bound nitrogen to N 2 . The influence of NO addition on the formation of N 2 O and N 2 was investigated in packed-bed gasification experiments using char prepared from a bituminous coal. The inlet concentration of NO was at a level typical for fluidized-bed combustion. It was found that NO reduction on char surface was strongly enhanced in the presence of oxygen. The majority of the added NO was converted to N 2 , but some N 2 O was also formed. The temperature-governed trade-off between emissions of NO and N 2 O, and the formation of N 2 O and N 2 from NO reduction, are qualitatively explained on the basis of known heterogeneous and homogeneous NO/N 2 O chemistry.

Trade-Off Between NOx and N2O in Fluidized-Bed Combustion of Coals

Combustion properties of upgraded alternative biomasses by washing and steam explosion for complete coal replacement in coal-designed power plant applications

Sludges from the papermaking industry represent a challenging residue stream that is difficult to dewater using conventional processes. The successful development and scale-up of innovative processes from lab- to pilot- to industrial-scale are required to tackle challenges for waste treatment, including paper sludges. Biological paper sludge was treated via a mild hydrothermal carbonization process (TORWASH®) to improve dewaterability of the sludge, including long-duration, continuous testing. Initial lab-scale experiments indicated the optimal treatment temperature for sludge dewatering was 190 °C. Dewaterability improved with increasing temperature, but the obtained solid yield decreased. Scaling-up to a continuous flow pilot plant required a temperature of 200 °C to achieve optimum dewatering. Pilot-scale hydrothermal treatment and dewatering resulted in solid cakes with an average dry matter content of 38% and a solid yield of 39%. This study demonstrates the benefits of hydrothermal carbonization for the dewatering of biological paper sludge without the use of dewatering aids such as fiber sludge or polyelectrolytes. The results also demonstrate the successful adaptation of a lab-scale batch process to a pilot-scale continuous flow process for hydrothermal carbonization of industrial wastewater sludge.

/pdf/development-of-a-continuous-hydrothermal-treatment-process-213io4rh.pdf

J.R. Pels

Papers

Evolution of nitrogen functionalities in carbonaceous materials during pyrolysis

NO and N2O decomposition over coal char at fluidized-bed combustion conditions

Trade-Off Between NOx and N2O in Fluidized-Bed Combustion of Coals

Combustion properties of upgraded alternative biomasses by washing and steam explosion for complete coal replacement in coal-designed power plant applications

Development of a Continuous Hydrothermal Treatment Process for Efficient Dewatering of Industrial Wastewater Sludge