(Invited) Redesigning of the Electrode/Membrane Interface Using Patterned Polymer Electrolyte Membrane for Fuel Cells

Abstract

For the realization of commercially viable polymer electrolyte membrane fuel cells (PEMFCs), it is essential that the development of PEMFCs capable to exhibit high performance over long-term operation with minimal use of precious metal-based catalysts. To achieve this, substantial efforts have been devoted to the development of highly active catalysts for oxygen reduction reaction (ORR). Thanks to recent advances in nanotechnology, novel Pt-based catalysts exhibiting high ORR mass activity that exceed the U.S. Department of Energy (DOE) activity target standard (0.44 A mgPt -1 at 0.9 VIR-free) have been reported. However, it is uncertain whether these advanced catalysts can be used as a substitute in practical applications because the practical applicability of the PEMFCs is eventually determined by the performance at much higher current density (HCD, > 1.5 A cmgeo -2), unlike the kinetic activity test condition (several mA cmgeo -2). Therefore, from more practical point of view, improvement of the HCD performance of PEMFC plays a key role in realizing commercially viable PEMFC. The HCD performance is highly affected by the ion conduction and mass transport of the reactant gases and water through the membrane electrode assembly (MEA). Particularly, it has been recently found that the mass transport limitations become more severe as the catalyst loading decreases, because of the reduced active sites available for the electrochemical reaction due to decreased active material loading. Therefore, it is critical to alleviate transport-related problems that lead to the cell potential drop at HCD to realize the high-performance PEMFC with minimal use of precious metal catalysts.Since the charge and mass transport are greatly influenced by not only the characteristics of the key components like catalysts, membranes, and gas diffusion layers, but also the structure of the MEAs. Particularly, the interface between the electrode and the electrolyte membrane has a considerable impact on the electrochemical characteristics of the PEMFC. As a result, there is a growing research activity to engineer this interface to enhance the practical performance of the PEMFCs. One promising approach to redesign the electrode/membrane interface is the introduction of 3-D patterned membrane surface. In recent years, our group has employed various structural patterns to the polymer electrolyte membrane, from simple line and prism structures to micro-nano multiscale architectures. We have applied them to various polymer electrolyte membrane-based fuel cell systems, like PEMFC, DMFC, and AEMFC. Regardless of the applied structure and the system, it is demonstrated that properly redesigned electrode/membrane interface using the patterned membrane significantly improves not only the HCD performance related to the mass transport through the MEAs, but also contact between the two layers, which can contribute to enhance the durability of the PEMFCs. In addition, the guided cracking technique introduced by combining the patterned membrane and simple mechanical stretching can improve the performance and durability of various type of fuel cells.