An on-line study of fuel cell behavior by thermal neutrons

Generating electricity via electrochemical conversion of chemical energy within a fuel cell is a very promising approach, which is investigated in many laboratories worldwide. Although the fuel cell principle has been known since many years, dedicated studies are needed to make this technology competing and cost efficient. Especially, low-temperature fuel cells have gained interest as high-efficiency converters for mobile and portable applications. These polymer electrolyte fuel cells and direct methanol fuel cells operate in the temperature regime below 100 degrees C at-or slightly above-ambient pressure. Therefore, the coexistence of a liquid aqueous phase and a gaseous phase inside the fuel cell is possible. The operation under two-phase flow conditions is believed to seriously impede the electrochemical performance due to mass transport limitations. Hence, an experimental method to study these two-phase flow phenomena in situ is highly desirable. It is possible to investigate the water distribution inside an operating fuel cell by means of neutron imaging methods. This way, dedicated performance parameters can be applied to the fuel cell and the two-phase flow phenomena are studied in situ, with reasonable spatial and time resolution. Appropriate post-processing allows quantitative evaluation, which is essential for the understanding of the relation between flow characteristics and electrochemical behavior of the cell. For this paper, the investigation of the two-phase flow inside the anodic compartment of a direct methanol fuel cell has been chosen in order to quantitatively demonstrate the suitability of neutron imaging with thermal neutrons