Jens Peter Paraknowitsch

Ionic Liquids as Precursors for Nitrogen-Doped Graphitic Carbon

Nitrogen-containing carbons are exciting materials, as theinclusion of nitrogen can improve the properties of bulk carboninseveralmaterialsapplications.Indeed,dependingontheamountof nitrogen incorporated, the properties of carbon can be alteredandoftenenhancedforaspecialpurpose.Forexample,importantproperties such as the conductivity, basicity, oxidation stability,andcatalyticactivityareaffectedwhennitrogenisintroducedintobulk carbon.

Metal-Free Heterogeneous Catalysis for Sustainable Chemistry

The current established catalytic processes used in chemical industries use metals, in many cases precious metals, or metal oxides as catalysts. These are often energy-consuming and not highly selective, wasting resources and producing greenhouse gases. Metal-free heterogeneous catalysis using carbon or carbon nitride is an interesting alternative to some current industrialized chemical processes. Carbon and carbon nitride combine environmental acceptability with inexhaustible resources and allow a favorable management of energy with good thermal conductivity. Owing to lower reaction temperatures and increased selectivity, these catalysts could be candidates for green chemistry with low emission and an efficient use of the chemical feedstock. This Review highlights some recent promising activities and developments in heterogeneous catalysis using only carbon and carbon nitride as catalysts. The state-of-the-art and future challenges of metal-free heterogeneous catalysis are also discussed.

Noble-metal-free electrocatalysts with enhanced ORR performance by task-specific functionalization of carbon using ionic liquid precursor systems.

The synthesis and characterization of functionalized carbon using variable doping profiles are presented. The hybrids were obtained from nitrile-functionalized ionic precursors and a ferric chloride mediator. This way, novel nitrogen doped and nitrogen-sulfur, nitrogen-phosphorus, and nitrogen-boron codoped carbon hybrids with a morphology containing microporous nanometer-sized particles were obtained. As-prepared heteroatom doped carbons exhibited superior electrocatalytic activity toward the oxygen reduction reaction (ORR) in alkaline and acid electrolytes. In particular, both the heteroatom type and iron were found to play crucial roles in improving the catalytic activity of functionalized carbon. It is worth noting that sulfur-nitrogen codoped functionalized materials synthesized in the presence of ferric chloride showed higher activity and stability in comparison to those of the commercial state-of-the-art Pt catalyst in alkaline electrolyte. Moreover, in acid electrolyte, sulfur-nitrogen codoped catalyst rivaled the activity of Pt with a stability outperforming that of Pt. Our X-ray photoelectron spectroscopy (XPS) investigation revealed a distinctive atomic structure in nitrogen-sulfur codoped material in comparison to other codoped catalysts, most likely explaining its superior electrocatalytic activity. This work presents a novel toolbox for designing advanced carbon hybrids with variable heteroatom doping profiles which presents tunable and enhanced ORR performance.

Nitrogen- and phosphorus-co-doped carbons with tunable enhanced surface areas promoted by the doping additives.

1-Butyl-3-methyl-pyridinium-dicyanamide (BMP-dca) is carbonised with tetra-alkyl-phosphonium-bromide additives yielding nitrogen- and phosphorus-co-doped carbons with enhanced BET surface areas promoted by the additives.

Intrinsically Sulfur- and Nitrogen-Co-doped Carbons from Thiazolium Salts

Carbon materials that are intrinsically co-doped with nitrogen and sulfur heteroatoms are synthesised by facile annealing of nitrile-functionalised thiazolium salts. Extremely high degrees of doping are achieved, especially for sulfur. The method further allows for direct tuning of the amounts of both N and S, establishing a new synthetic pathway in the emerging field of S-doped carbon materials.

Mesoporous Nitrogen Doped Carbon Supported Platinum PEM Fuel Cell Electrocatalyst Made From Ionic Liquids

A multitude of new and improved catalyst materials and concepts for membrane fuel cells were developed over the last decade. The requirements of these catalysts are low cost, high activity and durability. For example, platinum based catalyst concepts such as Pt monolayer catalysts, 2] Pt skin catalysts, Pt multimetallic catalysts, and dealloyed bimetallic Pt core-shell nanoparticle catalysts show promising activities based on Pt mass and Pt surface area for the oxygen reduction reaction (ORR). Furthermore, non-noble metal catalyst concepts could reduce the costs, but they currently still do not meet the activity targets for commercial fuel cell electrocatalysts. To improve the durability of fuel cell catalysts, also the support material is becoming more important. Oxidation resistance of the support material is one point of concern. Alternatives to pure carbon blacks (e.g. Vulcan XC 72R) were evaluated for the oxygen reduction, such as carbon nanotubes, 24] silicon carbide derived carbons, hollow spherical carbons, nitrogen modified carbons, or titanium-based materials. Especially nitrogen doped carbons show interesting properties like high conductivity, mesoporosity and the opportunity to adjust the nitrogen content in the support material. In this communication, we report the synthesis of a mesoporous nitrogen doped carbon supported platinum catalyst (Pt/ meso-BMP) based on an ionic liquid as nitrogen/carbon precursor and the evaluation of the catalytic system for ORR. Further, we analyzed the long-term behavior of this new catalyst and compared it with commercial high surface area carbon (HSAC) supported platinum catalyst. The mesoporous nitrogen doped carbon supported platinum nanoparticle fuel cell electrocatalyst (Pt/meso-BMP) was prepared by a two-step synthesis, as shown in Figure 1. In the first step, the mesoporous nitrogen doped carbon material (meso-BMP) was synthesized corresponding to the reference 35] by using N-butyl-3-methylpyridinedicyanamide (BMPdca) as ionic liquid compound. As evaluated by X-ray photoelectron spectroscopy (XPS) and elemental analysis (EA) the nitrogen content of 14.2 wt. % (XPS)/17.2 wt. % (EA) is very high. The variation of the values can be explained by the surface specificity of XPS measurements. In the second step, platinum nanoparticles were deposited on the meso-BMP substrate. The deposition of Pt occurred by a wet impregnation–freeze-drying method and followed by thermal annealing in a reductive atmosphere. Shown in Figure 2 are the XRD profiles for meso-BMP and Pt/meso-BMP. The as synthesized meso-BMP support material exhibits broad XRD reflections at 2 q= 26.1 and 42.98 corresponding to the inter (002) and intra (101) lattice planes of graphitized carbon. The reference powder diffraction patterns of (111), (200), and (220) lattice planes for pure face centered Figure 1. Synthesis route for mesoporous nitrogen doped carbon supported platinum nanoparticle catalyst.

A Tetrathiafulvalene (TTF)‐Conjugated Microporous Polymer Network

Conjugated microporous polymer networks have been prepared from the strong electron donor tetrathiafulvalene (TTF) and 1,3,5-triethynylbenzene (TEB) by using the Sonogashira-Hagihara cross-coupling reaction. Optimization of reaction conditions yields polymers with surface areas of up to 434 m(2)  g(-1) . The strong electron-donating properties of the network can be proven by iodine exposure. Structural and electronic changes due to formation of the charge-transfer salt from TTFs in the porous network and iodine within the pores are investigated.

Synthesis of mesoporous composite materials of nitrogen-doped carbon and silica using a reactive surfactant approach

Mesoporous composite materials of nitrogen-doped carbon and silica were synthesised in a one-step-process applying a soft templating procedure. The template used in the sol–gel synthesis of the silica is a cationic surfactant with distinct reactivity to form nitrogen-doped graphitic carbon upon heating. This reactivity is derived from the combination of the dicyanamide anion with a nitrogen-containing pyridinium cation, as it is known from ionic liquids used as nitrogen-doped carbon precursors. Thus applying this surfactant in a conventional sol–gel synthesis yields a silica gel doped with a precursor for N-doped carbon. By subsequent annealing mesoporous composite materials of silica and nitrogen-doped carbon are obtained.