Polar and dispersion interactions at carbon surfaces: further development of the XPS-based model

Bradley, R.H.; Daley, R.; Goff, F Le

doi:10.1016/s0008-6223(01)00267-6

Cited by 19 publications

(20 citation statements)

References 19 publications

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“…2a the experimentally determined Àh i (H 2 O) values increase in direct proportion to the surface oxygen levels of the CBs which is a marked contrast to the Àh i (Tol) figures. The water values are close to those previously reported for a wide range of carbon blacks of various types and levels of oxidation measured by XPS [19] and are also consistent with studies by other authors based on pH pzc and temperature programmed desorption of oxygen complexes [5,26,27].…”

Section: Resultssupporting

confidence: 92%

“…2a, for water and toluene, leads to the following which is consistent with previously reported relationships [3,19,28,29]:…”

Section: Resultssupporting

confidence: 91%

“…The material used in this study has an intrinsic surface oxygen level of 1.7 at.% measured by X-ray photoelectron spectroscopy (XPS). Ozonation of this material in a fluidised bed system of the type described in previous publications [19] for duration times of 5, 10, 30 and 60 min leads to surface oxygen levels of 7.3, 8.1, 10.3 and 11.2 at.%. Adsorption of the alcohols onto a graphitized (2973 K) carbon black, Cabot N234G, has also been investigated.…”

Section: Methodsmentioning

confidence: 73%

“…N330 has a Cabot quoted surface area of 77 m 2 g À1 and has been used in several previous adsorption studies where areas of 80.0 m 2 g À1 (±8 m 2 g À1 ) have been reported from nitrogen adsorption isotherm analysis using both BET and a s methods [18,19]. The material used in this study has an intrinsic surface oxygen level of 1.7 at.% measured by X-ray photoelectron spectroscopy (XPS).…”

Section: Methodsmentioning

confidence: 99%

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Specific and non-specific interactions on non-porous carbon black surfaces

Andreu

Stoeckli

Bradley

2007

Carbon

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The interactions which occur between methanol, ethanol or propanol and the surfaces of non-porous carbon blacks with increasing levels of oxygen chemistry have been studied using adsorption isotherm analysis and immersion calorimetry. Surface oxygen has been controlled by ozone treatment and characterised using X-ray photoelectron spectroscopy, which gives a direct and quantitative measure of surface composition from first-principles, and has not yet been extensively employed in detailed carbon adsorption studies. Nitrogen adsorption at 77 K and heat of immersion Àh i (mJ m À2 ) data for toluene, show that the physical structure of the carbon blacks is not modified by ozone treatment. A systematic shift to higher adsorption values, due to increasing specific hydrogen bonding interactions between the alcohol -OH groups and surface oxygen, is observed in all of the alcohol isotherms as the total oxygen content of the carbon surfaces ([O] T /at.%) increases. This effect is most significant for methanol confirming that the mechanism of adsorption is dominated by hydrogen bonding and therefore dependant on the surface concentration of oxygen sites. It is also observed for ethanol and propanol but is less marked due to the increasing non-specific, dispersion, interactions of the alkyl chain with the non-polar carbon surface. This description is in agreement with the data obtained for the specific enthalpies of immersion Àh i (mJ m À2) into the alcohols and into water or toluene which allow a semi-quantitative assessment off the relative polar and dispersion contributions to the overall interactions as functions of both carbon surface oxygen composition and the molecular structure of the alcohols. An overall correlation is observed between adsorption behaviour, [O] T /at.%, the resulting Àh i values and the characteristic energy E (kJ mol À1 ) of the DRK equation. It is also observed that the values of the affinity coefficient b DRK increase directly as a function of [O] T indicating that this latter parameter may provide a basis for predicting the adsorption isotherms of certain polar vapours on non-porous carbon surfaces. The effects of carbon surface chemistry on the character of adsorption isotherms, which change from Type III for the base N330 (and for a graphitized carbon black N234G) to Type II for the oxidised N330 materials, is discussed and the resulting effects on the surface area parameters S DRK and S BET (m 2 g À1 ) are considered.

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Section: Resultssupporting

confidence: 92%

“…2a, for water and toluene, leads to the following which is consistent with previously reported relationships [3,19,28,29]:…”

Section: Resultssupporting

confidence: 91%

Section: Methodsmentioning

confidence: 73%

Section: Methodsmentioning

confidence: 99%

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Specific and non-specific interactions on non-porous carbon black surfaces

Andreu

Stoeckli

Bradley

2007

Carbon

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“…However, it is recognized that both oxidizing agents impart the hydrophilicity to the carbon surface. [34][35][36][37][38][39] Thus, we might conclude that the excessive hydrophilicity of the carbon surface was one of the highly potential candidates for the cause of the degrada- tion that gives rise to flooding, although the carbon surface oxidation mechanism in the practical PEFC system should be clarified in future studies. There might be several ways to prevent the carbon oxidation on the surface exposed to the gas phase in the CL.…”

Section: A184mentioning

confidence: 99%

Carbon Surface Oxidation by Short-Term Ozone Treatment for Modeling Long-Term Degradation of Fuel Cell Cathodes

Maruyama¹,

Umemura²,

Inaba³

et al. 2009

J. Electrochem. Soc.

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In regard to degradation phenomena in a polymer electrolyte fuel cell ͑PEFC͒, there is little information on voltage loss due to the excess accumulation of liquid water blocking pores for the gas supply in the cathode ͑flooding͒ observed in a long-term operation over 5000-10,000 h. In this study, modeling of this degradation phenomenon was attempted using ozone treatment of the cathode catalyst layer ͑CL͒. The hydrophilicity of the layer was increased by the treatment, which was attributed to oxidation of the carbon surface of the catalyst ͑Pt-loaded carbon black, Pt/C͒ exposed to the gas phase in the CL. The flooding was observed at the PEFC with the cathode CL formed using 10 wt % Pt/C and treated with ozone for 10 h, and the extent of the flooding was enlarged by the ozone treatment of 15 h. The flooding was caused by the 5 h ozone treatment when the Pt content was 20 or 50 wt %. These results indicated that modeling of the long-term degradation was achieved by the short-term ozone treatment, and that the excessive hydrophilicity of the carbon surface of Pt/C was one of the highly potent candidates for causes of the degradation.Polymer electrolyte fuel cells ͑PEFCs͒ have recently been in practical use in power sources of electric vehicles and cogeneration systems for domestic electricity and heating, although the scale of PEFC usage is very limited. 1 Because the PEFC converts chemical energy to electricity by H 2 oxidation at the anode and O 2 reduction at the cathode in high efficiency with only water exhausted, 2-4 the substitution of conventional energy systems by the PEFC would help to improve the global environment. 5 In the next stage of the realization of the practical use of the PEFC, it is necessary to increase the number of the PEFC systems by gaining reliability and reducing the cost of the system. Durability of the PEFC closely relates to the reliability and the cost reduction. To obtain information about avoiding degradation of the PEFC and producing durable PEFCs, there have been an increased number of studies on the degradation mechanism at the components of the PEFC. 6 Nevertheless, several degradation phenomena occurring during a long-term operation have not clarified yet. One of those is the voltage loss at the cathode due to blocking of pathways for O 2 transfer by liquid water ͑flooding͒, which often begins to be observed for the operation over 5000-10,000 h in the state-of-the-art PEFC, 7 less than the PEFC-lifetime target of 40,000-90,000 h for the stationary PEFCs. Few studies have been reported so far on the mechanism of this degradation phenomenon and on the place causing the degradation.The O 2 transfer pathways are pores inside the cathode. They are faced with the surface of the catalyst particles consisting of Pt or Pt alloy supported on carbon black ͑hereafter called Pt/C͒ and the surface of the polymer electrolyte covering Pt/C in the catalyst layer ͑CL͒, and the surface of carbon and the fluorinated resins in the gas-diffusion layer. In the case of the PEFC degradation that give...

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Surface Chemistry of Carbon Materials

Bandosz

2008

Carbon Materials for Catalysis

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Polar and dispersion interactions at carbon surfaces: further development of the XPS-based model

Cited by 19 publications

References 19 publications

Specific and non-specific interactions on non-porous carbon black surfaces

Specific and non-specific interactions on non-porous carbon black surfaces

Carbon Surface Oxidation by Short-Term Ozone Treatment for Modeling Long-Term Degradation of Fuel Cell Cathodes

Surface Chemistry of Carbon Materials

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