Engineered Interfacial and Structural Porous Media Architecture for Polymer Electrolyte Fuel Cells

Open Access
Author:
Manahan, Michael Peter
Graduate Program:
Mechanical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
March 11, 2013
Committee Members:
  • Matthew M Mench, Dissertation Advisor
  • Jack Brenizer Jr., Committee Chair
  • Md Amanul Haque, Committee Member
  • Michael Anthony Hickner, Committee Member
Keywords:
  • polymer electrolyte fuel cell
  • diffusion media
  • laser
  • electrochemical energy
  • interface
  • interfacial modification
  • hydrogen
Abstract:
The purpose of this work is to explore engineered interfacial and structural architecture in fuel cell diffusion media. Emerging electrochemical storage and conversion devices have been under significant development in the past two decades, and the optimization of the interfacial and structural properties of their components presents a complex, multidisciplinary challenge. Interfaces in electrochemical devices must transport heat, mass, and current in an optimized manor to help sustain the electrochemical reaction and efficient operation. Engineering the interfacial and structural architecture of components in electrochemical devices such as fuel cells can yield significant performance breakthroughs that will make them increasingly economically viable for commercial implementation. This dissertation investigates engineered interfacial and structural architecture in fuel cell materials, namely the catalyst layer (CL) and the diffusion media (DM). Cracks were introduced in the CL in order to modify the CL|DM interface. The gas-phase transport and performance of cracked CL was compared to a standard CL. Based on insights gained from the cracked CL investigation, the diffusion media were modified using laser treatment. Perforations were introduced via lasers on samples of virgin DM that contained hydrophobic content. Depending on laser choice, some laser-cut samples displayed a “heat affected zone” (HAZ) at the catalyst layer | microporous layer interface, characterized by a region surrounding each perforation where hydrophobic content was removed. Experimental techniques such as polarization testing, electrochemical impedance spectroscopy, neutron radiography, Tafel slope analysis, and others were used to characterize the impact of the laser-modified DM and give fundamental insight into the modified multi-phase transport. A key result of this dissertation proved a 25% increase in power density by optimizing the perforation diameter and the diameter of the heat affected zone. It was shown that the perforation and the heat affected zone uniquely contribute to the performance changes. Namely, the perforation allows for membrane rehydration while the cell is operated with 50% relative humidity inlet gas streams and the heat affected zones redistribute and retain liquid water, leading to improved gas-phase transport. Experiments were conducted to understand the fundamental transport characteristics.