Transport in fuel cell ion exchange membranes

Abstract

Proton-exchange membrane fuel cells (PEMFCs) are promising as high-efficiency energy conversion devices, but the need for expensive noble metal catalysts such as Pt has hindered commercialization. An alternative is the alkaline membrane fuel cell (AMFC), which intrinsically possesses faster kinetics at the cathode, enabling noble metals to be replaced by Co, Ag, Fe, or Ni. In order to compete with PEMFCs (i.e. achieve 1.0 W/cm² power density), AMFCs require improved membranes. In particular, membranes must achieve conductivities of ~0.1 S/cm and be thermally, chemically, and mechanically stable. The membrane mass transport phenomena governing conduction should be clearly understood in order to efficiently develop new materials. In particular, there is need for an improved, molecularlevel understanding of the relationship between membrane water content and membrane conductivity, as well as an elucidation of the kinetic mechanism causing membrane carbonation. The dependency of conductivity on membrane water content is explored using Fourier Transform Infrared Attenuated Total Reflectance (FTIR-ATR) spectroscopy with twodimensional correlation techniques, and Electrochemical Impedance Spectroscopy (EIS). The particular role that specific water cluster states play during transport is elucidated, and the transient behavior associated with membrane carbonation is explored.

Key findings

• ▸The relationship between membrane water content and conductivity is complex and requires a molecular-level understanding.
• ▸The kinetic mechanism causing membrane carbonation is not fully elucidated and requires further investigation.
• ▸Improved membranes with conductivities of ~0.1 S/cm and thermal, chemical, and mechanical stability are necessary for AMFCs to compete with proton-exchange membrane fuel cells (PEMFCs).

Keywords

Identifiers

DOI

10.17918/etd-3898

Journal

Unknown journal

Year

2011