Experimental Assessment of Pt Utilization

A survey of studies that focus on Pt utilization and effectiveness factors can be found in Eikerling et al. (2008) and Xia et al. (2008). In the past, ambiguous definitions of catalyst utilization have been circulating with inconsistent values having been reported. This could lead to a wrongful assessment as to how much the performance of fuel cells could be improved by advanced structural design of catalyst layers. Without any doubt, the accurate distinction and determination of catalyst utilization and effectiveness factors have a major impact on defining priorities in catalyst layer research. 

Pt utilization is a statistical property of the CCL. It can be obtained from ex situ electrochemical studies. It is defined as the ratio of the electrocatalytically active surface area, accessible to electrons and solvated protons, to the total surface area ofPt  

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 purpose of studying Pt utilization in the catalyst powder is to evaluate the electronic connectivity of carbon/Pt and maximum ionic accessibility of Pt nanoparticles. Pt utilization of 100% means that all Pt nanoparticles are connected to the electronic conduction network, with the entire Pt surface accessible for protons. Close to 100% Pt utilization in the catalyst powder of carbon-supported Pt, immersed in liquid electrolyte, is possible, since only a negligible fraction of the Pt surface is covered by carbon particles. For Pt nanoparticles, supported by a polymer material such as poly(3,4-ethylenedioxythiphene)/poly(styrene-4-sulfonate), Pt utilization was reported to be 43-62%. 

Various parameter definitions are used to specify the intrinsic activity of a catalytic material. Many practical studies, focusing on comparing catalyst materials under conditions that are typical for PEFC operation, provide values of current densities measured at a certain cathode potential, often chosen as 0.9 V vs. SHE. 

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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. ... 

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