Reaction engineering perspective of PEM fuel cells: The stirred tank reactor as a building block

A differential polymer electrolyte membrane (PEM) fuel cell reactor was designed and constructed based on the reaction engineering stirred tank reactor. The fuel cell operated under well-mixed conditions and was one-dimensional (only spatial gradients transverse to the membrane arise). The steady state current in the fuel cell depended on the initial water content in the membrane, indicating that the water balance within the fuel cell gave rise to steady state multiplicity. The fuel cell's dynamic respond to changes in external load, temperature, and reactant flows showed that various tune scales were associated to water transport and water absorption in the membrane. This suggested that the fuel cell membrane behaved like a reservoir for water and the membrane needed time to equilibrate to changes in operating conditions. The reactor also exhibited autonomous oscillations that were attributed to the interplay of the transport processes and mechanical relaxation of the membrane. This is an abstract of a paper presented at the 228th ACS National Meeting (Philadelphia, PA, 8/22-26/2004).