Study of proton conductivity in catalyst layer using AC impedance and catalyst dispersion using USAXS & cryo-TEM

Yun Zhou, Purdue University

Abstract

My thesis consists of two parts work centered on the catalyst layer of polymer electrolyte membrane (PEM) fuel cell. The first part is the study of the interaction of different catalyst ink components via the ultra small angle X-ray scattering (USAXS) and cryo-TEM. One of the major aims of this work is to fill the gap between the catalyst layer on MEA and the catalyst ink. The dispersion of carbon aggregates in liquid media was studied using USAXS. A systematic approach was taken to study the dispersion of a simple ink system (i.e. carbon black + glycerol and carbon black + ethanol) first, then adding Nafion ionomer, at last the Pt/C catalyst ink system. Multiple curve fitting were used to obtain the particle size, geometry and size distribution from the USAXS scattering data. The results indicate that the Nafion ionomer and solvent had great influence on carbon particle aggregation, size distribution. There was a general interaction among each component. The cryo-TEM, by which the size and geometry of particles in a liquid can be directly observed, was used to validate the scattering results, which showed an excellent agreement. The second part of my study is the ionic conductivity of catalyst layer. This method of measuring the conductivity within a catalyst layer was developed based on the Los National Laboratory (LANL) conductivity test. It can effectively avoid the ionic conductivity contribution from Nafion membrane. From the measurement results, it is found that both the proton and the electronic conductivity change with binder content. At the same time, to simulated the testing conditions are close to the working conditions of the real fuel cell. The results have a significant meaning of improving conductivity of protons in a fuel cell catalyst layer. The results showed that sulfonic acid functional group modified XC-72 carbon black has a probability of replacing or partially replacing the Nafion ionomer in catalyst ink preparation.

Degree

M.S.M.S.E.

Advisors

Youngblood, Purdue University.

Subject Area

Chemical engineering|Energy|Materials science

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