# A Novel Method to Indirectly Measure Electro-osmotic Drag and Back Diffusion From Total Water Flow Experiments in PEM Fuel Cells

## TL;DR

This paper introduces a new method to measure water flow in fuel cells, improving accuracy in predicting water management and preventing membrane issues.

## Contribution

The paper proposes a higher-order polynomial data fit to accurately separate electro-osmotic drag and back diffusion in PEM fuel cells.

## Key findings

- Prior assumptions about negligible drivers were likely incorrect, affecting coefficient measurements.
- The new method enables more accurate prediction of total water flow from each driver.
- Improved water management can reduce risks of cathode flooding and membrane dry-out.

## Abstract

The objective of
the research is to quantify the electro-osmotic
drag and back diffusion portions of the experimentally measured total
water flow across a proton exchange membrane. Part of the deficiency
of prior research calculated individual coefficients by forcing trendlines
through the origin that implicitly assumes other drivers to be negligible.
If one or more other drivers are present, their impact will be lumped
in with the intended coefficient measurement. Also, using linear trendlines
assumes that the indirectly measured coefficient does not change with
current density, which is likely the case for liquids but not for
vapor. For fuel cell membranes like Nafion, the electro-osmotic drag
and back diffusion coefficients are dependent on the hydration state
of the membrane. To overcome this dependency, a higher-order polynomial
data fit is used for the total water flow. A methodology of combining
the theoretical model with experimental data sets is proposed here
to determine the component coefficients at each data point. Applying
this method to prior data reveals that other fluid drivers assumed
to be negligible were likely not so. A more accurate understanding
of electro-osmotic drag and back diffusion in turn enables more accurate
prediction of total water flow from each driver, leading to improving
water management and reducing the risks of cathode catalyst layer
flooding and membrane dry-out.