Statistical utilization factor

What is the physical meaning of the factor Tstat in Equation 3.6 The statistical utilization factor Tstat stands for the fraction of the catalyst surface that is wetted by electrolyte and accessible for protons needed in the ORR. It corresponds to the utilization factor introduced in the section Experimental Assessment of Pt Utilization.  

In the original structure-based CCL model of Eikerling and Kornyshev (Eikerling and Kornyshev, 1998 Eikerling et al., 2004, 2007a), an expression for Tstat was derived based on the theory of active bonds in random three-phase composite media. 

In this approach, discussed in the section Effective Catalyst Layer Properties from Percolation Theory, Tstat corresponds to the statistical fraction of Pt particles at or near the triple-phase boundary of solid carbon/Pt phase (volume fraction Xptc), ionomer phase (A /), and pore space (Xp = 1 — Xptc — Xei). 

In realistic CCL structures, application of percolation laws to parameterize the composition dependence of Tstat is disputable due to two crucial assumptions, which start to seem insufficient in the light of more detailed knowledge of the CL structure. The first assumption is that protons needed for the ORR are available only inside 

As for the first assumption, the electrolyte phase must be treated as a mixed phase. It consists of a thin-film structure of ionomer at the surface of Pt/C agglomerates and of water in ionomer-free intra-agglomerate pores. The proton density is highest at the ionomer film (pH 1 or smaller), and it is much smaller in water-filled pores (pH 3). However, the proton density distribution is not incorporated in the statistical utilization Tstat, but in an agglomerate effectiveness factor, defined in the section Hierarchical Model of CCL Operation.  

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This test statistic utilizes a continuity correction factor of 0.5 as well. As described by Fleiss et al. (2003), the test performs well when expected cell counts within each of H 2 x 2 tables differ by at... 

The statistical surface area utilization factor Fstat has been considered under different conditions, specifically in catalyst powders and in MEAs of operational PEFCs. The electrocatalytically active surface area in the catalyst powder can be obtained from the charge under the H-adsorption or CO-stripping waves measured by... 

The catalyst layers evaluated in this model-based analysis are not intended to represent the best-in-class in terms of performance. Instead, the experimental studies were picked out from the literature because they provided porosimetry as well as performance data. Nevertheless, the low value of the CL effectiveness factor is a striking result of this analysis. The value of Fcl decreases from 4 % at jo < 0.4 A cm to 1 % aty o 1 A cm . This parameter incorporates statistical effects and transport phenomena across all scales in the CCL. The values found are consistent with an experimental evaluation of effectiveness factors by Lee et al. (2010) if the values found in that study are corrected with the atom utilization factor F p, the agreement is very good. The low value of Fcl suggests that tremendous improvements in fuel cell performance and Pt loading reduction could be achievable through advanced structural design of catalyst layers. 

The practice of estabHshing empirical equations has provided useflil information, but also exhibits some deficiencies. Eor example, a single spray parameter, such as may not be the only parameter that characterizes the performance of a spray system. The effect of cross-correlations or interactions between variables has received scant attention. Using the approach of varying one parameter at a time to develop correlations cannot completely reveal the tme physics of compHcated spray phenomena. Hence, methods employing the statistical design of experiments must be utilized to investigate multiple factors simultaneously. 

The primary optimization target of CLs is the effectiveness factor of Pt utilization, Tcl- It includes a factor, that accounts for statistical limitations of catalyst utilization that arise on a hierarchy of scales, as specified in the following equafion. defermines the exchange current density ... 

Austria, France, Germany, Italy, Slovakia, the Czech Republic and Hungary. Likewise, the reserves in the USA and Canada are 17% and 19.1% respectively. Nevertheless, statistical analysis shows that European UGS have been under-utilized during the latest years. That s why it is recommended for operators to justify planning margins through cost-benefit analysis and other affecting factors, in the liberalized conditions of new gas markets. 

Regression is a highly useful statistical technique for developing a quantitative relationship between a dependent variable (response) and one or more independent variables (factors). It utilizes experimental data on the pertinent variables to develop a numerical relationship showing the influence of the independent variables on a dependent variable of the system. 

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