Operando Liquid Pressure Determination in Polymer Electrolyte Fuel Cells

Area of Science:

• Electrochemistry
• Materials Science
• Fluid Dynamics

Background:

• Fuel cell performance at high current densities is limited by water removal from gas diffusion layers, preventing flooding.
• Understanding dynamic water cluster formation is crucial for optimizing gas diffusion layer properties.

Purpose of the Study:

• To investigate the dynamic mechanisms of water cluster formation and pressure evolution within fuel cell gas diffusion layers.
• To elucidate the relationship between water cluster dynamics, capillary pressure, and breakthrough pressure during operation.

Main Methods:

• Utilized X-ray tomographic microscopy at 1 Hz frequency for in situ observation of water cluster formation.
• Employed interfacial curvature analysis and volume-of-fluid simulations to assess water phase pressure evolution.
• Compared operando breakthrough pressure with static ex situ capillary pressure measurements.

Main Results:

• Observed increased capillary pressure as water fronts navigated pore throats.
• Detailed the interplay between water volume and pressure during droplet formation and feeding path instability.
• Measured a 2 kPa higher breakthrough pressure during dynamic invasion compared to static evaluations.

Conclusions:

• Dynamic liquid water invasion in fuel cell gas diffusion layers differs significantly from static models.
• The findings necessitate a re-evaluation of gas diffusion layer design for improved water management and performance.
• Optimizing pore structure and surface properties can mitigate water cluster instability and flooding.