Nitrogen-doped coatings on carbon nanotubes and their stabilizing effect on Pt nanoparticles

Tuaev, Xenia; Paraknowitsch, Jens Peter; Illgen, René; Thomas, Arne; Strasser, Peter

doi:10.1039/c2cp40760d

Cited by 93 publications

(65 citation statements)

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“…The P-doping -in agreement with the results for nitrogen-doping discussed in the previous sections of this manuscript 25 -provides a better dispersion of the particles on the CNTs, and better stability during methanol oxidation that also occurs with higher efficiency compared to Pt particles loaded on non-functionalised CNTs.…”

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confidence: 76%

“…This could be proven on carbon nanotubes modied with ionic liquid derived N-doped carbon using time resolved in situ small angle X-ray scattering, clearly pointing out a signicant increase of stability of the particles against coarsening and agglomeration achieved by the N-doping. 25 As the development of noble metal free catalysts might still be facing certain challenges, this concept shows that N-doped carbon can also be applied in a kind of bridging technology.…”

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confidence: 99%

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Doping carbons beyond nitrogen: an overview of advanced heteroatom doped carbons with boron, sulphur and phosphorus for energy applications

Paraknowitsch

Thomas

2013

Energy Environ. Sci.

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Heteroatom doped carbon materials represent one of the most prominent families of materials that are used in energy related applications, such as fuel cells, batteries, hydrogen storage or supercapacitors. While doping carbons with nitrogen atoms has experienced great progress throughout the past decades and yielded promising material concepts, also other doping candidates have gained the researchers' interest in the last few years. Boron is already relatively widely studied, and as its electronic situation is contrary to the one of nitrogen, codoping carbons with both heteroatoms can probably create synergistic effects. Sulphur and phosphorus have just recently entered the world of carbon synthesis, but already the first studies published prove their potential, especially as electrocatalysts in the cathodic compartment of fuel cells. Due to their size and their electronegativity being lower than those of carbon, structural distortions and changes of the charge densities are induced in the carbon materials. This article is to give a state of the art update on the most recent developments concerning the advanced heteroatom doping of carbon that goes beyond nitrogen. Doped carbon materials and their applications in energy devices are discussed with respect to their boron-, sulphur-and phosphorus-doping. Broader contextThe research and design of novel materials that are applicable in various energy devices represent one of the central and most thriving subjects within today's scientic work. The challenges do not only rely on the tremendous need to overcome traditional fossil fuel based energy recovery. While a lot of sustainable concepts already exist, these require the development of high performance materials that are able to cope with certain challenges, e.g. the dependence on highly expensive and rather not abundantly available noble metals, and also a lack of long term stability of those. Researchers have been carrying out numerous studies concentrating on nding alternative materials that can be applied in novel energy devices. Those alternative materials should most preferably be free of noble metals, avoid expensive precursor systems, be sustainable and not rely on the fossil energy sources that are to be replaced, and of course exhibit high activity in the devices they are designed for. One class of materials in whose development and understanding researchers have put strong effort is heteroatom-doped carbon materials. By heteroatom doping the properties are altered compared to crude carbon materials. The by far most intensely studied doping candidate is nitrogen, capable of not only increasing electric conductivity, but also the catalytic activity of carbons. Such N-doped carbons have advanced tremendously in the past few years, especially by proving their usefulness as electrocatalysts for the reduction of oxygen in fuel cell cathodes, or as electrode materials in supercapacitors. Meanwhile the spectrum of doping has been widened, and novel doped carbons have been reported, indicating the promising pote...

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confidence: 76%

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confidence: 99%

Doping carbons beyond nitrogen: an overview of advanced heteroatom doped carbons with boron, sulphur and phosphorus for energy applications

Paraknowitsch

Thomas

2013

Energy Environ. Sci.

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1,645

999

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“…The fresh Co-doped Pt/CCC shows an initial Pt-rich layer thickness of $0.75 nm. From density functional theory simulations, it has been postulated that the optimized Pt skin thickness is 2 to 3 monolayers which is equal to 0.50-0.75 nm [71,72]. It has also been reported that the ligand effects are only effective up to 1-3 atomic layers [69] and the geometric effects can modify the Pt-Pt interatomic distances up to 7 atomic layers [73].…”

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Highly Active and Durable Co-Doped Pt/CCC Cathode Catalyst for Polymer Electrolyte Membrane Fuel Cells

Jung

Xie

Kim

et al. 2015

Electrochimica Acta

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A B S T R A C TCathode catalyst based on Co-doped Pt deposited on carbon composite catalyst (CCC) support with high measured activity and stability under potential cycling conditions for polymer electrolyte membrane (PEM) fuel cells was developed in this study. The catalyst was synthesized through platinum deposition on Co-doped CCC support containing pyridinic-nitrogen active sites followed by controlled heattreatment. High resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) studies confirmed uniform Pt deposition (Pt/CCC catalyst, d Pt = 2 nm) and formation of Co-doped Pt/CCC catalyst (d Pt = 5.4 nm) respectively. X-ray energy dispersive spectrometry (XEDS) line-scan studies showed the formation of Co-core Pt-shell type catalyst with a Pt-shell thickness of $0.75 nm. At 0.9 V iR-free , the Co-doped Pt/CCC catalyst showed initial mass activity of 0.44 A mg Pt À1 and 0.25 A mg Pt À1 after 30,000 potential cycles between 0.6 and 1.0 V corresponding to an overall measured activity loss of 42.8%. The commercial Pt-Co/C showed initial mass activity of 0.38 A mg Pt À1 and $70% loss of activity after 30,000 cycles. The enhanced catalytic activity at high potentials and stability of mass activity for the Co-doped Pt/CCC catalyst are attributed to the formation of compressive Pt lattice catalyst due to Co doping. The Co-doped Pt/CCC showed stable open circuit potential close to 1.0 V under H 2 -air with an initial power density of 857 mW cm À2 and only 16% loss after 30,000 cycles. Catalyst durability studies performed between 0.6 and 1.0 V indicated that Co doping increased the onset potential for PtO 2 formation close to 1.0 V vs. reversible hydrogen electrode (RHE). The enhanced catalytic activity and stability of Co-doped Pt/CCC catalyst are attributed to (i) higher onset potential for PtO 2 formation resulting in less PtO 2 formation during potential cycling which alleviates Pt dissolution in the reverse scan (ii) higher stability of CCC used as a support compared with commercially used supports, and (iii) optimized electrochemical properties of the catalyst and the support which result in synergistic effect between pyridinic nitrogen catalytic sites from the Co-doped CCC support and compressive Pt-lattice catalyst.

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“…IL based syntheses of carbon materials have been established in manifold ways in recent years of research. [1][2][3][4][5][6][7][21][22][23][39][40][41][42][43][44][45][46][47][48] Especially liquid salts with dicyanamide anions are a powerful precursor for N-doped carbons, [1][2][3][4][5][6][7] and for advanced co-doping with S. 27 Herein we present a modified IL route using phosphonium additives, paving the way towards P-and N-co-doped carbonsa class of materials only rarely reported in the literature so far. 36 BMP-dca with 40 mol% of tetrabutyl-phosphonium-bromide (TBuPBr) as a phosphorus source was therefore carbonised at 1000 1C in a constant flow of inert gas (see ESI † for details).…”

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

et al. 2013

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Herein we present a modified IL route using phosphonium additives, paving the way towards P-and N-co-doped carbonsa class of materials only rarely reported in the literature so far. 36BMP-dca with 40 mol% of tetrabutyl-phosphonium-bromide (TBuPBr) as a phosphorus source was therefore carbonised at 1000 1C in a constant flow of inert gas (see ESI † for details). The black solid product is a carbonaceous material exhibiting a local graphitic order that is limited in its extension. This can be derived from the powder X-ray diffraction (PXRD) patterns showing broadened, but intense, (002) and (100) reflexes typical for a stacking motif in turbostratic-like carbons (compare Fig. S1, ESI †). The black product was also characterised by means of elemental combustion analysis (EA) and inductively coupled plasma optical emission spectrometry (ICP-OES) to determine the degree of heteroatom-doping: 4.1 wt% of N-doping (EA) and 5.7 wt% of P-doping (ICP-OES) are revealed. The material is thus successfully dually doped; especially the remarkably high degree of P-doping compared to other approaches 36-38 is noteworthy and points out the advantages of the method. To also prove the homogeneity of the material, elemental mapping based on energy dispersive X-ray spectroscopy (EDX) and wavelength dispersive X-ray spectroscopy (WDX) was performed. The data are provided in the ESI † (Fig. S2-S5, ESI †), showing clearly that the dopants are spread homogeneously throughout the material. Significant local concentration maxima cannot be found. The binding environments of both N and P could be elucidated by X-ray photoelectron spectroscopy (XPS), and the detailed N1s and P2p scans are depicted in Fig. 1. The results for nitrogen are as expected according to our previous studies:1,2,27,46 three deconvolved contributions appear at 398.13 eV, 400.88 eV and 402.80 eV that can be assigned to pyridinic and pyrollic nitrogen species, quaternary graphitic nitrogen and minor oxidised nitrogen binding motifs (due to oxidative processes on the surface of the materials), respectively. 16,34,49,50 The N doping thus occurs with N atoms firmly bound to the carbon backbone. To clearly assign the P2p XPS scan to certain chemical environments is however more difficult. Fig. 1 Deconvolved XPS scans of the N1s and P2p orbitals of the material.

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Nitrogen-doped coatings on carbon nanotubes and their stabilizing effect on Pt nanoparticles

Cited by 93 publications

References 38 publications

Doping carbons beyond nitrogen: an overview of advanced heteroatom doped carbons with boron, sulphur and phosphorus for energy applications

Doping carbons beyond nitrogen: an overview of advanced heteroatom doped carbons with boron, sulphur and phosphorus for energy applications

Highly Active and Durable Co-Doped Pt/CCC Cathode Catalyst for Polymer Electrolyte Membrane Fuel Cells

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

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