Water Visualization and Flooding in Polymer Electrolyte Membrane Fuel Cells Brian Holsclaw West Virginia University Department of Chemical Engineering
Overview Background Objective Experimental Conditions PFR Cell CSTR Cell Conclusions and Further Work Questions
Overview Background Objective Experimental Conditions PFR Cell CSTR Cell Conclusions and Further Work Questions
Schematic of a PEMFC Operation - + e - e - - Membrane + Hydrogen-rich fuel (H 2 + impurities) Anode e - e - e - H + H + H + e - e - e - Oxygen (Air) + impurities Cathode H 2 2H + +2e - O 2 + 4H + + 4e - 2H 2 O Catalyst (Pt)
PFR PEM Fuel Cell Plug Flow Reactor (PFR) Modeled as sum of differential elements along tube length Varying concentrations and conditions Used in commercial designs Channels can be easily clogged by water flooding Need water for membrane Two-phase flow in channels
CSTR PEM Fuel Cell Continuous Stirred-Tank Reactor (CSTR) Perfect mixing assumed Constant conditions in cell Can be treated as differential element of more complicated or larger design No channels for flooding Vertical inlet/outlet allows cell to auto-drain water Water can collect if inlet/outlet in horizontal position
Overview Background Objective Experimental Conditions PFR Cell CSTR Cell Conclusions and Further Work Questions
Project Objective Visualize water droplet formation patterns in PFR and CSTR designs Measure currents in different areas of membrane electrode assembly (MEA) when flooding Measure performance changes during water draining Demonstrate how fuel cell position affects flooding
Overview Background Objective Experimental Conditions PFR Cell CSTR Cell Conclusions and Further Work Questions
Experimental Conditions Room temperature Neat H 2 and O 2 used No external humidification system at steady state (except when flooding) Hydrogen flowrate: 6 ml/min Oxygen flowrate: 3 ml/min Constant load resistance of 0.1 Ω
Overview Background Objective Experimental Conditions PFR Cell CSTR Cell Conclusions and Further Work Questions
Vertical PFR Orientation Performance stable at ~400 ma and 0.041 V (0.1 Ω) after 24 hr Water formation only on cathode side (from reaction) Several leaks around probes (square peg in round hole) Silicone sealant used Equal distribution of droplets around membrane area Cathode View
Horizontal PFR Orientation Should not be gap here Inlet - right, outlet - left Initial runs with wrong flow plate (not true PFR) Droplets in top of picture: normal operation there Decline from 400 ma to 336 ma after 24 hr Cell drained itself within hour of this picture Flooded Cathode View No draining performance change
Cathode Performance Horizontal PFR Orientation (wrong plate)
Cathode During Flooding Cathode After Flooding Horizontal PFR Orientation Correct size flow plates Critical Droplet
Cathode Performance Horizontal PFR Orientation Current (ma) 300 250 200 150 100 Final Performance = 160 ma Cathode 1 Cathode 2 Cathode 3 Cathode 4 Cathode Total 50 0 0 4 8 12 16 20 24 Time (hr)
Current (ma) 300 250 200 150 100 Anode Performance Horizontal PFR Orientation No overall jump Local Current Jump Anode 1 Anode 2 Anode 3+4 Anode Total 50 0 0 4 8 12 16 20 24 Time (hr)
Overview Background Objective Experimental Conditions PFR Cell CSTR Cell Conclusions and Further Work Questions
Vertical CSTR Orientation Cathode CSTR view (vertical) Anode CSTR view (vertical) Wires into probes were loose fitting and tended to come out very easily Something in the wiring/setup caused noise in the data Performance dropped from 300 ma to 230 ma in 48 hours in vertical position
Cathode View Horizontal CSTR Orientation Performance fluctuated between 235 215 ma over 24 hr Too much noise in data No way to check if wires are attached without taking apart cell (putting back together might make them loose again) No significant performance change when rotated to vertical position to allow draining
Overview Background Objective Experimental Conditions PFR Cell CSTR Cell Conclusions and Further Work Questions
Conclusions Performance drops while flooding PFR (wrong plate) steady but small drop PFR (correct plate) large drop in stages CSTR small drop if any Best performance when water droplets found all over membrane Good visualization of water droplets but results too inconsistent Cell performance might not match visual clues
Problems, Difficulties, Trouble Only one membrane used for all tests Performance degraded with membrane use Needed to run cell polarization tests to determine before/after membrane changes Contact problems with probes Use parts that fit correctly Always fix the leaks
Further Work Redo all experiments with new membrane Redesign cells so wires will fit better, no leaking, and no view obstructions Obtain data acquisition board able to handle more channels (better data) Use different wire setup to avoid noise Use thinner gaskets to get better probe contact
Special Thanks Professor Jay Benziger Erin Kimball Barclay Satterfield NSF and Princeton University
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