A Method to Account for the Effects of Electro-Osmotic Drag and Back Diffusion in PEM Fuel Cells

Abstract

The objective of this research is to quantify the separate effects of electro-osmotic drag (EOD) and back diffusion (BD) on the net water flow across a proton exchange membrane (PEM) where these effects occur simultaneously. The solution here is to detail a method to decompose the net water flow into component drivers without making assumptions regarding the various coefficients, and instead relying on data mining to isolate the EOD and BD contributions. The net water flow across the membrane is a function of current density and water concentration differences, represented as a surface for which slopes can be determined in the direction of constant current to isolate BD, and constant concentration difference to determine EOD. This method also can be used to determine the hydration state of the membrane as well as determining which EOD and BD coefficient empirical models are valid under certain conditions. With a clearer understanding of net water flow, EOD and BD, the water balance of the fuel cell can be improved which will lead to improved fuel cell operation.