Evaluation of Neutron Imaging for Measuring Phosphoric Acid Distribution in High Temperature PEFCs

P Boillat,A Kaestner,J Biesdorf,T J Schmidt,P Oberholzer

doi:10.1149/2.023403jes

Abstract

The possibility of using neutron imaging for non-invasive investigation of the phosphoric acid distribution in high temperature polymer electrolyte fuel cells (HT-PEFC) was explored with a small scale test cell. In particular, the issue of providing a suitable reference – necessary for distinguishing the neutron attenuation due to the acid from the attenuation due to the structural components – was solved by using in situ deuteration/protonation of the phosphoric acid, a fully reversible process. Experiments with a non-operating cell have shown that this isotope exchange can be performed in less than 20 minutes. The possibility of imaging the acid distribution either over the cell area (through-plane imaging) or across the cell structure (in-plane imaging) was demonstrated. Although some discrepancies between the two modes remain, quantitative analysis resulted in a good agreement with the amount of acid used in the cell.

Highlights

Where δ is the measured thickness, I is the intensity measured in the work image, I0 is the intensity measured in the reference image and is the attenuation coefficient of the measured material
First evaluations were done concerning the ability of neutron imaging to quantify the amount of phosphoric acid
The obtained results are in quite good agreement with the expected amount of phosphoric acid in the membrane electrodes assemblies (MEAs) the absolute accuracy of the determination needs some more verification

Summary

Exposure time

13.5 μm μm μm s ratio H3PO4:PBI is approx. 5:1 resulting in approx. 10 mgH3PO4 cm−2membrane) and two ELAT based electrodes using 0.5 mg cm−2 20% Pt/Vulcan XC 72 in the catalyst layers (BASF Fuel Cell). Where δ is the measured thickness, I is the intensity measured in the work image, I0 is the intensity measured in the reference image and is the attenuation coefficient of the measured material This equation does not account for beam hardening, but according to a calculation based on the experimental white beam spectrum, and on the energy dependent detector sensitivities and hydrogen cross sections, the resulting error is less than 5% for the range of optical densities (

Exp Setup Dewpoint

Results and Discussion

Conclusions