Multi-Walled Carbon Nanotube Nanoforests as Gas Diffusion Layers for Proton Exchange Membrane Fuel Cells

Abstract

Proton exchange membrane fuel cells (PEMFCs) are emerging as power conversion devices for stationary, automotive, and portable devices compared to other types of fuel cells. The PEMFCs operate at elevated temperatures to improve the conductivity of the electrolyte and enhance the kinetics of electrode reactions resulting in higher operating efficiencies. However, operation at elevated temperatures requires external humidification to fully humidify the reactant gases to avoid low proton conductivity which results from membrane dehydration. Gas diffusion layers (GDLs) have been developed to manage water as well as to promote gas distribution to the active catalyst regions in an attempt to obtain higher power density at all current density regions. For several years, carbon papers or carbon cloth substrates (macroporous layer) with polytetrafluoroethylene (PTFE) based microporous layer coatings have been the major choice for GDLs. This research focuses on implementing carbon nanotube nanoforests (CNNs) as GDLs in order to increase fuel cell performance in terms of stability, humidity, power density, and operation efficiency, while lowering the weight, size, and costs. Multi-walled carbon nanotubes (MWCNTs), used in this research, have been proven to transport large currents with low resistance, have extremely high hydrophobic properties and inherent oxidation resistance, all of which make the potential application of MWCNTs as GDLs very promising.