Physics of Pumping Methanol/Water Solutions for Fuel Cell Applications

Proton exchange membrane fuel cells are environmentally friendly energy conversion devices. A special class of PEMFCs, direct methanol fuel cells (DMFCs), oxidize liquid methanol solutions at the cell anode as opposed to hydrogen gas. The use of methanol as fuel makes DMFCs highly attractive for portable applications due to the high volumetric energy density of liquid methanol. Previous work has shown that electroosmotic (EO) pumps can be used to pump pure methanol to obtain relatively high flow rates per power in applications with minimal pressure loads. This study explores the unique aspects of pumping methanol/water solutions for fuel cell applications with non negligible pressure loads. We explore EO pump figures of merit pertinent to portable fuel cell applications including flow rate per power and the ratio of EO pump power to fuel cell power. Experimental studies reveal EO pump power to DMFC power ratios of 5% or less for borosilicate glass substrates. Further, we will discuss unique aspects of pumping low ion density methanol/water solutions that affect EO pump performance including solution conductivity and transient pH gradients. Ultimately this work provides a theoretical and experimental basis for a miniature DMFC system using an EO pump for fuel delivery.