Surface areas carbons

These data show that, indeed, mesopores dominate except in zeolites and active carbons. Surface areas can be very high viz., up to a few football fields per kg ). 

Carbon comes in many forms and surfaces areas. Graphite can have surface area below 1 m2/g, while high surface area carbon blacks approach 2000 m2/g. If Pt adsorbs onto carbon at the same surface density, the Pt loading (Pt, wt%) will then be a function of the carbon surface area. Assuming that CPA can be adsorbed onto carbon at 1.6 mmol/m2, and PTA at 0.84 mmol/m2 at the respective SEA conditions, plot Pt (wt%) vs. surface area of carbon. 

Ball et al. investigated the effect of carbon surface area on carbon corrosion at 1.2 V for 24 h and found that, for commercial carbon blacks, cumulative carbon corrosion correlated with carbon BET (Brunauer Emmett Teller) area, although when analyzed as specific carbon corrosion (weight of carbon corroded per unit of carbon area), some variation was observed. The effect of Ft on carbon corrosion has also been studied and conflicting results have been reported. Roen, Paik, and Jarvi found that Ft did increase carbon corrosion... 

Specific carbon surface area (Vulcan/Gr-Vulcan) cm2c/mgc 2400/800... 

The gas-phase treatment enhances the catalytic activity of the carbon. However, it is difficult to attribute this enhancement to only one feature of the treated carbon, i.e., chemical or physical characteristics. The activation of the raw sample leads to an increase in surface area and pore volume as well as to an increase in the surface functionalities. The literature shows no consensus on the correlation between the NO conversion and the carbon surface area [8, 9]. In this case, the surface area of sample SC900R is about twice as large as that of sample SC900 but the NO conversion increases approximately four times. The contradictory findings in the literature and the results showed here lead to believe that the chemical characteristics of the functional groups are an important element for the NO removal performance of the carbons. 

Carbon Surface area (m-7g) Pore volume (cm Vg) pH v< Carbon surface charge" (mmol/g) Adsorbent/adsorbate complex charge (rnmo)/g) Adsorbed NOM charge" (mmol/g)... 

In the literature it has been suggested that the late reactivity maximum around XssO.7 (see Figure 4A) results from the saturation of the carbon surface area with catalytically active alkali species, (See, e,g., Hamilton et al. ) This explanation, however, is not supported by the catalyst accumulation factors (= [l+(bt) ]) derived by us as we find them to rise steadily with increasing conversion degree (See Figure 4C). Catalyst saturation may be defined as a state where the charcoal surface area is covered entirely by a mono-layer of catalytic species. If we assume the extreme case that carbon, but not the added alkali species, is being removed from the charcoal, then, from the initial atom ratio it follows that saturation effects may be encountered, but not before ca. 88% of the carbon has been consumed by the gasification reaction. 

Material balance gives the following equations. Assuming that carbon used in the experiment consists of spherical particles, CO evolution rate at time t, nt, is proportional to the product of carbon surface area at time t, St, and the rate constant at time t, kt. 

The difference in the yields of products appears to be a carbon surface area effect that acts as product-determining characteristics. 

Activated carbon surface area 1000 to 1500 mVg pore volume 0.6 to 0.8 cmVg, temperature <540°C superficial gas velocity 100 to 600 dmVm -s capacity depends on organic range... 

Activated carbon surface area 1000 to 1500 m /g pore volume 0.6 to 0.8 cm /g, temperature < 540 °C loading very dependent on molar mass of target solute, solubility in the carrier liquid and pH. Example loading 0.01 kg organic molar mass 100/kg dry solid. The value varies with the molar mass . Carbon usage expressed as kg carbon required/m liquid increases with increase in the TOC in the feed and depends on the type of species present. A gross approximation is that 1 kg/m is required for 300 mg TOC/L with n = 1.0 for the range 200-30000 TOC, mg/L. acid treated clay surface area 225 to 300 m /g. 

A downward trend of specific catalytic activity when carbon surface area is increased is observed. This behaviour can be attributed to many factors, but the authors emphasized that the particle size (indicated in the labels of Fig. 7.7) and... 

Carbon is generally used as catalyst support material because of its high electric and thermal conductivity, chemical stability, and porous structure [11]. The catalytic activity of the catalyst layer increases with increasing carbon surface area due to better platinum dispersion. High surface area carbon blacks such as Ketjenblack and Vulcan are therefore preferred in PEMFC application. However, carbon is thermodynamically unstable at normal cathode potentials between 0.5 and 1V. As shown in Figure 20.1a, carbon is oxidized to carbon dioxide (CO2) or carbon monoxide (CO) at high electrode potentials whereas it is reduced to methane (CH4) at low electrode potentials. The following reactions are relevant for fuel-cell operation ... 

To account for the cathode CL (PEM) transport properties changes induced by carbon corrosion (ionomer degradation) we can use, for example, spatially-averaged fractal representations of the CLs to describe the impact of carbon (ionomer) mass loss on the microstructural properties changes, such as the evolution of the carbon instantaneous surface area or effective diffusion coefficients in the CL. We have used this approach for example ini d68,i79 relate the temporal evolution of the cathode thickness and carbon surface area with the carbon corrosion kinetics, by representing the carbon phase as a two-dimensional Sierpinski carpet projected in the cathode thickness direction (Fig. 11.11). 

For example, within this context, CGMD simnlations have been used to build up a stmctural database for CLs with different carbon contents in terms of interpolated mathematical functions describing the impact of the carbon mass loss (induced by corrosion) on the evolution of the ionomer coverage on Pt and carbon, the electronic conductivity of the CB, the effective O2 diffusion properties, the carbon surface area and the Pt surface area (which re-organizes during the carbon corrosion process) (see Fig. 11.9, 11.12). These functions are then integrated into the MEMEPhys kinetic model to simulate the impact of carbon corrosion on the MEA performance decay. ... 

The instantaneous MEA materials structural evolutions (e.g. ECSA, carbon surface area, PEM porosity) in the simulated PEMFC operation, induced by catalyst dissolution and ripening, carbon corrosion and PEM chemical degradation, are determined at each simulation time-step as functions of the elementary degradation chemistry kinetic equations as described. ... 

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