Mass activity

It is also convenient to compare the behavior of different dispersed catalysts with the help of the two following quantities the mass activity, MA, in Ag", and the specific activity, SA, in pA The values ofMA... 

Specific Activity (SA) and Mass Activity (MA) of Pt Electrocatalysts Supported on Different Carbon Powders Characterized by Specific Surface Area (S) and Particle Size (d)... 

In order to obtain high mass activity of Pt, it is essential to disperse Pt or alloy nanoparticles on high surface area supports. Some questions then arise. What kind of alloys and composition should we choose Is there any good parameter for screening the catalysts What size of catalyst particles should we prepare to obtain the maximum performance Unfortunately, there has been much controversy about such issues in the literature. 

The mass activity MA (in A g ) of the Pt catalyst is, of course, the product of the specific activity js (in A m ) and the specitic surface area 5mass (in ni g ) MA = js mass- Because S ass is inversely proportional to the particle diameter dpt, the use of supported Pt nanoparticles is effective for increasing MA, if js is a constant independent of dpt- However, even at pure Pt, conflicting results on the values of js and P(H202) have been reported, suggesting the presence of differences in electrochemical properties between bulk and supported nanoparticles. For example, Bregoli [1978]... 

Analytical methods for quantifying americium in environmental samples are summarized in Table 7-2. The methods that are commonly used in the analysis of americium based on activity are gross a analysis, a-spectrometry and gamma-ray spectrometry. MS detection techniques are used to measure the mass of americium in environmental samples. (The mass-activity conversion factor for 241Am is 0.29 (lCi/ lg or 3.43 ig/ p,Ci [Harvey etal. 1993]). 

A strong caveat to this prediction is the role of active surface area to the actual activity observed in fuel cells. This is often termed the mass activity— that is, the activity per mass of active metal (usually Pt), which has a direct correlation to cost. Mass activity is a combination of specific activity and surface area ... 

Oxygen reduction mass activities of dealloyed ternary Pt alloy catalysts as cathodes in MEAs at 80°C, 150 kPa Oj. (R. Srivastava et al., Angewandte Chemie International Edition (2007), 46,8988. Copyright Wiley-VCH Verlag GmbH Co. KGaA. Reproduced with permission.)... 

Activated alumina is amorphous or crystalline alumina, which has been partially or com-pletly dehydrated and has a large surface area per unit mass. Activated alumina is made from hydrated alumina, namely, A1203. H20, where n =1-3, by calcining to get n closeto 0.5 (Knaebel, 1995). It is a white or tan-colored material of chalky appearance. 

Write down all of the calculations required to determine the identity of the metal chloride in the Determination of Molar Mass activity (eChapter 11.9). Use similar calculations to identify the alkaline earth metal chloride that gives a solution with osmotic pressure of 1.32 atm upon addition of 100.0 mg to water under the same conditions of volume and temperature. 

Figure 17 shows the measured spatially resolved mass activity map for the aged MEA from the controlled start-stop test in comparison with a new one.55 It also indicates more carbon loss near the anode inlet, because one can easily imagine that when carbon support particles collapse, the platinum particles can come in contact with one another, which leads to coalescence of the platinum... 

Figure 17. Mass activity distribution maps for both new and aged MEAs showing impact of 200 unmitigated start-stop cycles. Test conditions rcen = 80 °C, dewpt = 85 °C (anode and cathode), P = 250/270 kPaa, s (anode/cathode), high stoichiometry flow for anode (H2) and cathode (O2).

Figure 19. Predicted carbon loss distribution along anode flow-field channel over a complete H2/air-front start—stop cycle using the pseudo-capacitance model in comparison with one-dimensional, normalized mass activity from Fig. 17. The pseudo-capacitance value used in the model is obtained from AC-impedance measurements as described in references (42, 43).

Figure 9.6 Polarization curves for the ORR on Pd/C (ETEK, line a), Pt/C (ETEK, line b), and Pd3Fe/C NPs (line c) in 0.1 M HC104. Sweep rate 10 mV s-1 room temperature. The Pd or Pt loading is 10 (jig cm 2. Inset Comparison of mass activity for Pt/C (ETEK), Pd3Fe/C, and Pd2Co/C at 0.8 and 0.85 V.111 (Reprinted with permission from M. Shao et al., J. Am. Chem. Soc. 2006, 128, 3526-3527. Copyright 2006 American Chemical Society.)...

The latter activation technique uses more silicon in the process of direct synthesis (70-75% against 30-40% for nonactivated mass) and considerably increases the yield of dialkyldichlorosilanes. For example, if for the normal mass during the synthesis of methylchlorosilanes the yield of di-methyldichlorosilane varies from 30 to 45% in time, for the mass activated by zinc chloride the yield grows up to 60-75%. However, this activation technique also has disadvantages ... 

Heat time 0.25 M water 2ogr1 Absorbance concentration mass activity... 

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