Experimental Analysis of Transient Water Fluxes in PEM Fuel Cells

• Author / Creator

  Kracher, James R.

• Understanding the movement of water within a polymer electrolyte membrane (PEM) fuel cell is critical for improving performance at high loads. In this work, an experimental setup was designed and assembled for monitoring the in situ distribution of water contained within the anode and cathode of an operating PEM fuel cell. Relative humidity, temperature, and pressure sensors, housed within a heated water bath, characterize the water vapour levels evaporated in the reactant streams entering and leaving an operational fuel cell to provide transient measurements of the net movement of water across the PEM in addition to correlating operating anomalies with two-phase flow.

  Manufacturer accuracies were propagated with experimental uncertainties calculated from auxiliary experiments to estimate the setup's overall ability to correctly identify the water content of a gas stream, found to be ≤12.9%. Experimental validation comparing to conventional water collection techniques employed extensively in literature demonstrate the setup can successfully reproduce net crossover flux magnitudes and trends identified in other publications as well as reconcile the cumulative amount of water entering and leaving the cell.

  The setup was then used to investigate the effects of adding a microporous layer(MPL) to the net crossover flux across 5 cm2 membrane electrode assemblies with varying Nafion membrane thicknesses. The addition of a single MPL to the cathode significantly improved performance in the mass transport region. Results indicated MPLs have negligible impact on electronic resistances and instead encourage the transport of water across the PEM in the direction normal to the MPL. All tested membranes showed an increase in water transport towards the anode when the cathode was assembled with an MPL with thinner membranes exhibiting higher crossovers. Unprecedented high current densities for low loaded electrodes with NR211 membranes were achievable after the addition of an MPL to the cathode and by increasing the anode flow rate to accelerate convective drying, thereby establishing a concentration gradient that increased back diffusion and mitigated flooding in the cathode.

• Subjects / Keywords

  • Transient
  • Water Transport
  • Microporous Layer
  • Net Crossover Flux
  • PEM Fuel Cell
  • Two-phase Flow

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R34J0BD1M

• License

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