Pt-mass activity

Figure 9.8 Variation of Pt mass activity and activity of the Pt(lOO) surface for the...

Based on Eqn (3.7), the Pt-mass activity (ima,Pt) can be calculated using the following equation ... 

For Pt catalysts, generally to say, the smaller the Pt particles and the larger SSA the particles possess, the better the electro-catalytical performance would be. However, whether or not there exists a critical size that can give the maximum Pt-mass activity is still no clear answer yet, although extensive research efforts have been done on this subject. Calculation using density fimctional theory (DFT) is often used for providing insight into the effect of nanoparticle size on the electrocatalytical activity. ... 

Fig. 1.5 Methanol oxidation peak currents as a function of Pt coverage (4 nmol as 2D islands is approximately 0.8 of a monolayer), where If and Ib represent peak currents at forward and backward scans, respectively (a) Pt mass activity for methanol oxidation on commercial PtRu and PtML/Ru electrocatalysts (b) [77] (reproduced with permission from J. Electrochem. Soc. 155, B183 (2008). Copyright 2003, The Electrochemical Society)...

Fig. 18.5 (a) ORR voltammetry in 02-saturated 0.1 M HCIO4 of dealloyed PtCu3 catalysts using the alloy precursors annealed at 600, 800, and 950 compared to a commercial Pt catalyst. (Inset) CV curves of the dealloyed PtCu3 catalysts in N2 saturated 0.1 M HCIO4. (b) Comparison of Pt-mass activities at 0.9 V/RHE. (c) Comparison of Pt-area-specific activities at 0.9 V/RHE (reprint with permission from ref. [27])... 

Fig. 18.9 (a) Current-voltage characteristics of 10 cm single H2/O2 fuel cells using dealloyed PtCua, dealloyed PtNia, and dealloyed PtCos cathode catalyst, in comparison with standard Pt cathode catalysts, (b) Pt-mass activities at 0.9 V of the dealloyed Pt-bimetallic cathode catalysts (reprint with permission from ref [47])... 

Fig. 18.12 Stability measurement of various dealloyed PtCua and dealloyed PtCuCoa catalyst compared to pure Pt standard cathode catalysts in single fuel cell MEAs. The Pt-mass activities at 0.9 V are plotted before and after 30,000 voltage cycles (0.5-1.0 V, lOOmV s ). Cell conditions anode H2/cathode N2, 100 % relative humidity, 80 °C (reprint with permission from ref. [62])...

Fig. 19.7 LHS) (a and b) High-resolution STEM images of Pt hollow spheres and (c and d) line scans parallel and perpendicular to the lattice planes (RHS) comparison of the ESA of solid and hollow Pt spheres based on hydrogen desorption charges and ORR-specific and Pt mass activities measured at 0.9 V in RDE measurements [47]...

Fig. 23.7 Effect of potential cycling on Pt mass activity for ORR on different supports. Cycling condition, 0.1 M HCIO4 0.6-1.2 V/RHE for 5 s oxygen atm. and 25 °C [74]...

Perhaps the most pressing issue with regard to ORR electrocatalysts for PEMFCs is the slow, but drastic, decrease in the Pt mass activity with time, which has been... 

For carbon-based electrocatalyst supports, there is no question that advanced supports have been made that enhance the dispersion of Pt nanoparticles. Much of the time, this advanced dispersion has led to higher EGA compared to Pt/Vulcan and Pt/TKK however, this has not always translated into an increase in the Pt mass activity. Observations on Pt mass activity appear to be a balance between EGA and particle faceting, which plays a significant role in the ORR [166], as the particle size is altered at the same loading as Pt/G. In cases where the Pt mass activity was increased, the specific activity (when reported) always decreased, calling into... 

Gulla et al. have demonstrated superior performance and stabUily of carbonless thin layer electrodes made by a dual ion beam assisted deposition (IBAD) technique that combines physical vapor deposition (PVD) with ion beam bombardment [47]. They found that bilayered coatings on GDL with either a Co or a Cr iimer layer ( 50 nm thin) and a Pt outer layer ( 50 nm thin, and 0.08 mg Pt cm ) showed a more than 50% higher Pt mass activity at 900 mV than a Pt single layer. 

FIGURE 13.10 (a) High-resolution STEM image of a Pt hoUow particle, (b) Pt mass activity as a function of voltage cycling time (profile shown in figure) for hollow and sohd Pt nanoparticles. The average particle sizes were 6.5 and 3.2nm in diameter, respectively. Reprinted with permission from Ref. [90]. American Chemical Society. 

Electrocatalysts for the Oxygen Reaction, Core-Shell Electrocatalysts, Fig. 5 (a) Schematic representation of a subsurface modification of core, (b) Pt mass activities of Pt/C, Pt LPd/C, and PtMLPdIr/C at 0.9 V versus RHE [29]... 

Zhang et al. investigated Pt monolayer deposits on Pd(lll) single crystals (Pt/Pd(lll)) and on Pd/C nanoparticles (Pt/Pd/C) for ORR [18]. The ORR reaction mechanism of the mono-layer catalysts was found to be the same as that on pure Pt surface. Pt/Pd(lll) was found to have a 20 mV improvement in half-wave potential versus Pt(lll), and the Pt/Pd/C had a Pt-mass activity 5-8 times higher than that of Pt/C catalyst. The enhanced ORR activity is attributed to the inhibited OH formation at high potential, as evidenced from XAS measurements. In a real fuel cell test, 0.47gpt/kW was demonstrated at 0.602 V [21]. In a related study, the ORR on platinum monolayers supported on Au(lll),... 

Performance of PIml electrocatalysts has been determined using single-crystal surfaces [15], thin-film rotating disk electrode (RDE), and in fuel-cell membrane electrode assembly (MEA). Higher activities observed with rotating electrodes are ascribed to a better Pt utilization of Pt. Figure 6 displays the data on RDE and MEA prepared from Pt L/Pd/C nanoparticles 0.57 and 0.36 A/mgpt in Pt mass activities at 0.9 V were obtained from the measurements on RDE and MEA, respectively. 

MultimetaUic alloy nanoparticle cores, obtained by in situ decomposition of a Prussian blue analogue, e.g., PtML/AuNi0.5Fe, show a remarkable Pt mass activity as 1.38 A/mgpt... 

Fig. 10.5 (a) The schematic model of a Pt-Cu alloy particle before and after electrochemical dealloying of the near-surface Cu atoms (pink balls = Cu atoms gray balls = Pt atoms) (b) Pt mass activities of Pt-Cu/C catalysts at various annealing temperatures compared to that of Pt/C catalyst (Reproduced from [67]. With permission)... 

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